FIELD OF THE INVENTION

The present invention relates to a thin-film electroluminescent display ("TFEL") and more particularly to a thin-film electroluminescent display according to the independent claim 1. The present invention relates also to a method for a detecting one or more faults in a thin-film electroluminescent display, and more particularly to a method for a detecting one or more faults in a thin-film electroluminescent display according to the independent claim 13.

BACKGROUND OF THE INVENTION

In the prior art, thin-film electroluminescent displays are well known and robust emissive display devices that can withstand severe environmental factors like high and low temperatures, high pressures, shocks and vibrations. Both transparent and non-transparent thin-film electroluminescent displays are known. Transparent TFELs have excellent transparency characteristics, reaching photopic transmission of over 70%. Basic technology of TFELs dates back to 1980s, but important improvements are still being made, and many new applications for TFELs are found, for example in-glass laminated and optical applications, and the integration of touch functionality with the TFEL.

From the standpoint of addressing a certain picture element to produce light (be "on") or to remain dark (be "off") during the TFEL’s operation, two main categories exist: a segment TFEL display where the information is presented by turning on and off segments representing fixed symbols or pictograms (for example an arrow pointing up), and a matrix TFEL display where the information is generated by turning on and off pixels that, when combined, form symbols like letters, numbers and other pictograms to yield information. In general, segment displays can produce a brighter light output than their matrix counterparts, but naturally can only produce information which is available from their fixed set of symbols laid out on the display panel during the manufacturing of the display.

One of the problems associated with the prior art segment TFELs is that sometimes the segments fail. A healthy, operating light producing segment is essentially a plate capacitor with a common electrode and an overlapping segment electrode. Thus, the equivalent circuit of a segment electrode-common electrode pair may be well approximated with a capacitor.

A failed, non-healthy or non-operating segment may be approximated with a short circuit, or an open circuit, depending on the failure type.

With a short circuit type of failure, the segment and common electrodes may become adjoined with at least one electrically conductive pathway between the electrodes, the one or more pathways being created, for example, by some electrical breakdown or other failure in the thin film structure, e.g. caused e.g. by an impurity that has emerged into the TFEL structure during manufacturing, or by an accidental overvoltage caused, for example, by static electricity and poor shielding.

With an open circuit type of failure, the segment electrode, or the opposite common electrode, or both, may, at least partially, turn from an electrically conductive material to an electrically insulating material. Thus, the plate capacitor nature of the segment electrode-common electrode pair is destroyed, and what is left is an open circuit with no or very little electrical interaction between the remaining parts of the segment or common electrodes.

For the long-term operation of the TFEL display, detecting such failures is important, as driving a short-circuited or open-circuited load consumes power for no technical purpose, and may even cause the driving circuitry and the TFEL to fail. Measuring the electrical characteristics of a segment-common electrode pair directly from a segment electrode to the common electrode requires that each of the segment electrodes is separately connected to a measurement or diagnostic unit for determining the health of each of the segment electrodes. This is clearly problematic and requires extra circuitry.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a TFEL display and a method for detecting one or more faults in a thin-film electroluminescent display so that the problems related to the prior art mentioned above are solved or at least alleviated.

The objects of the invention are achieved by a thin-film electroluminescent display characterized by what is stated in the independent claim 1. The objects of the invention are further achieved by a method for a detecting one or more faults in a thin-film electroluminescent display characterized by what is stated in the independent claim 13.

The preferred embodiments of the invention are disclosed in the dependent claims. It has been surprisingly found that the health of each of the segment electrodes can be determined by driving a segment diagnostics signal to the segment electrodes and then determining the electrical behaviour of the common electrode relative to some reference voltage, e.g. ground, node. This requires very few extra interconnections as the segment electrodes can be fed, for diagnostics purposes, with the interconnections that already exist for light production.

As an aspect of the present invention, a thin-film electroluminescent display is disclosed. The thin-film electroluminescent display comprises

- a high voltage node supplying a driving voltage VH,

- a low voltage node supplying a low voltage VL,

- a high control voltage node supplying a high control voltage VC,

- a reference voltage node supplying a reference voltage VR, and

- a thin-film display element extending substantially along a base plane defining a lateral extension of the thin-film display element. The thin-film display element comprises

- a common layer comprising a common electrode, and

- a segment layer comprising segment electrodes, the segment electrodes arranged at least partially to laterally overlap with the common electrode. The thin-film display element comprises

- a luminescent layer arranged between the common layer and the segment layer, the luminescent layer arranged to produce visible light when a voltage difference exceeding a threshold voltage VT is arranged between the common electrode and the overlapping segment electrodes. The thin-film electroluminescent display comprises

- a segment driver arranged to feed a segment diagnostics signal to each of the segment electrodes, and

- a common driver comprising a common connection connected to the common electrode. The thin-film electroluminescent display comprises a diagnostic arrangement comprising a diagnostic connection connected to the common connection. The diagnostic arrangement is configured to determine an electrical determinant of the common connection relative to the reference voltage node, the electrical determinant caused by the segment diagnostics signal. The segment driver is arranged to feed the segment diagnostics signal to each of the segment electrodes, and the diagnostic arrangement is configured to detect a fault in the segment electrodes based on the electrical determinant. Advantage of the invention is that the TFEL display may be arranged to determine a failed segment or non-failed (healthy) segment easily based on the electrical behaviour of the common electrode. Thus, the measurement setup for determining the health of a segment can be provided with no additional, separate interconnections to each of the segment electrodes as the circuitry and interconnections for driving the segment electrodes for light production can be used.

In an embodiment of the thin-film electroluminescent display, the common driver is arranged to set the common connection to a high impedance state.

In an embodiment of the thin-film electroluminescent display, the common driver is arranged to set the common connection to a high impedance state, and the electrical determinant comprises a common connection voltage of the common connection relative to the reference voltage node. Thus, the determination of the segment health is done with the voltage of the common electrode versus a known, predetermined reference voltage.

In an embodiment of the thin-film electroluminescent display, the common driver is arranged to set the common connection to a high impedance state, and the electrical determinant comprises a common connection voltage of the common connection relative to reference voltage node such that the reference voltage node is the low voltage node. Thus, the determination of the segment health is done with the voltage of the common electrode versus a known, predetermined reference voltage, and the reference voltage can be e.g. the low voltage of the TFEL display.

In an embodiment, the reference voltage node has the voltage of the low voltage node.

In an embodiment of the thin-film electroluminescent display, the common driver is arranged to set the common connection to a high impedance state, and the electrical determinant comprises a common connection voltage of the common connection relative to reference voltage node such that the reference voltage node is a ground node with a zero voltage. Thus, the determination of the segment health is done with the voltage of the common electrode versus a known, predetermined reference voltage, and the reference voltage can be a ground (zero) voltage.

In an embodiment of the thin-film electroluminescent display, the segment driver is arranged to sequentially feed the segment diagnostics signal in a high diagnostics voltage state to each of the segment electrodes, and the diagnostic arrangement is configured to detect the fault in each of the segment electrodes based on the voltage of the common connection, the fault being an open circuit fault such that:

- the fault in the segment electrode is determined by a low control voltage state of the common connection voltage; or

- an operating segment electrode is determined by a high control voltage state of the common connection voltage, the operating segment electrode being one of the segment electrodes; or

- the fault in the segment electrode is determined by a low control voltage state of the common connection voltage, and

- an operating segment electrode is determined by a high control voltage state of the common connection voltage, the operating segment electrode being one of the segment electrodes. It is advantageous to compare the common connection voltage to a known reference voltage for fault detection purposes. It is also possible to detect, if a segment electrode has a fault or not, or do both determinations.

In an embodiment of the thin-film electroluminescent display, the diagnostic arrangement comprises a pull-up resistor configured to pull the diagnostic connection towards the high control voltage,

- the segment driver is arranged to sequentially feed the segment diagnostics signal in a low diagnostics voltage state to each of the segment electrodes, and

- the diagnostic arrangement is configured to detect the fault in each of the segment electrodes based on the voltage of the common connection, the fault being an open circuit fault such that:

- the fault in the segment electrode is determined by a stationary high control voltage state of the common connection voltage; or

- an operating segment electrode is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes; or

- the fault in the segment electrode is determined by a stationary high control voltage state of the common connection voltage, and

- an operating segment electrode is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes. It is advantageous to compare the common connection voltage to a known reference voltage when a healthy, operating segment is indicated with a dynamic, rising voltage behaviour.

In an embodiment of the thin-film electroluminescent display,

- the diagnostic arrangement comprises a pull-down resistor configured to pull the diagnostic connection towards the low voltage,

- the segment driver is arranged to feed the segment diagnostics signal in a high diagnostics voltage state to each of the segment electrodes, and

- the diagnostic arrangement is configured to detect the fault in the segment electrodes based on the voltage of the common connection, the fault being a short circuit fault, such that:

- the fault in at least one of the segment electrodes is determined by a stationary high control voltage state of the common connection voltage caused by the segment diagnostics signal in the high diagnostics voltage state short-circuited to the common electrode; or

- a state where all segment electrodes are operating is determined by a high control voltage state of the common connection voltage decaying to a low control voltage state due to the pull-down resistor discharging segment capacitors comprising the common electrode and the segment electrodes; or

- the fault in at least one of the segment electrodes is determined by a stationary high control voltage state of the common connection voltage caused by the segment diagnostics signal in the high diagnostics voltage state short-circuited to the common electrode, and

- a state where all segment electrodes are operating is determined by a high control voltage state of the common connection voltage decaying to a low control voltage state due to the pull-down resistor discharging segment capacitors comprising the common electrode and the segment electrodes. This is an advantageous way to quickly determine if none of the segments are faulty.

In an embodiment of the thin-film electroluminescent display,

- the diagnostic arrangement comprises a pull-down resistor configured to pull the diagnostic connection towards the low voltage,

- the segment driver is arranged to feed the segment diagnostics signal sequentially in a high diagnostics voltage state to each of the segment electrodes, and

- the diagnostic arrangement is configured to detect the fault in each of the segment electrodes based on the voltage of the common connection, the fault being a short circuit fault such that:

- the fault in the segment electrode is determined by a stationary high control voltage state of the common connection voltage caused by the segment diagnostics signal in the high diagnostics voltage state short-circuited to the common electrode; or

- an operating segment electrode is determined by a high control voltage state of the common connection voltage decaying to a low control voltage state due to the pull-down resistor discharging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes; or

- the fault in the segment electrode is determined by a stationary high control voltage state of the common connection voltage caused by the segment diagnostics signal in the high diagnostics voltage state short-circuited to the common electrode, and

- an operating segment electrode is determined by a high control voltage state of the common connection voltage decaying to a low control voltage state due to the pull-down resistor discharging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes. It is advantageous to compare the common connection voltage to a known reference voltage even if a healthy, operating segment is indicated with a dynamic, decaying voltage behaviour.

In an embodiment of the thin-film electroluminescent display,

- the diagnostic arrangement comprises a pull-up resistor configured to pull the diagnostic connection towards the high control voltage,

- the segment driver is arranged to feed the segment diagnostics signal in a low diagnostics voltage state to each of the segment electrodes, and

- the diagnostic arrangement is configured to detect the fault in the segment electrodes based on the voltage of the common connection, the fault being a short circuit fault, such that:

- the fault in at least one of the segment electrodes is determined by a stationary low control voltage state of the common connection voltage caused by the segment diagnostics signal in the low diagnostics voltage state short-circuited to the common electrode; or

- a state where all segment electrodes are operating is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging segment capacitors comprising the common electrode and the segment electrodes; or

- the fault in at least one of the segment electrodes is determined by a stationary low control voltage state of the common connection voltage caused by the segment diagnostics signal in the low diagnostics voltage state short-circuited to the common electrode, and

- a state where all segment electrodes are operating is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging segment capacitors comprising the common electrode and the segment electrodes. This is an advantageous way to quickly determine if none of the segments are faulty.

In an embodiment of the thin-film electroluminescent display,

- the diagnostic arrangement comprises a pull-up resistor configured to pull the diagnostic connection towards the high control voltage,

- the segment driver is arranged to feed the segment diagnostics signal sequentially in a low diagnostics voltage state to each of the segment electrodes, and

- the diagnostic arrangement is configured to detect the fault in each of the segment electrodes based on the voltage of the common connection, the fault being a short circuit fault such that:

- the fault in the segment electrode is determined by a stationary low control voltage state of the common connection voltage caused by the segment diagnostics signal in the low diagnostics voltage state short-circuited to the common electrode; or

- an operating segment electrode is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes; or

- the fault in the segment electrode is determined by a stationary low control voltage state of the common connection voltage caused by the segment diagnostics signal in the low diagnostics voltage state short-circuited to the common electrode, and

- an operating segment electrode is determined by a low control voltage state of the common connection voltage rising to a high control voltage state due to the pull-up resistor charging a segment capacitor comprising the common electrode and the operating segment electrode, the operating segment electrode being one of the segment electrodes. It is advantageous to compare the common connection voltage to a known reference voltage even if a healthy, operating segment is indicated with a dynamic, rising voltage behaviour.

In an embodiment of the thin-film electroluminescent display,

- the electrical determinant comprises a common connection current between the common connection and the reference voltage node; or

- the electrical determinant comprises a common connection current between the common connection and the reference voltage node such that the reference voltage node is the low voltage node; or

- the electrical determinant comprises a common connection current between the common connection and the reference voltage node such that the reference voltage node is a ground node with a zero voltage. In these embodiments, the determination of the segment health is done with the current from the common electrode (or specifically, from the common connection connected to the common electrode) to a known, predetermined reference voltage. The reference voltage can be e.g. the low voltage VL of the TFEL display, or the reference voltage may be ground (zero or GND) voltage.

In an embodiment of the thin-film electroluminescent display, the common driver comprises

- a low side switching element comprising:

- a low controlling node,

- a low first controlled node connected to the common connection through the diagnostic connection, and

- a low second controlled node. The low side switching element is arranged to connect the low first controlled node and the low second controlled node with a low-impedance connection when a voltage equal to or higher than a switching voltage is connected to the low controlling node, the common driver comprising

- a regulating resistor,

- a regulating NPN type BJT comprising:

- a base connected to the low second controlled node,

- an emitter connected to the reference voltage node, and

- a collector connected to the low controlling node; the regulating resistor being connected between the low second controlled node and the reference voltage node. The diagnostic arrangement comprises a voltage sensing unit arranged to sense the voltage of the low controlling node. The segment driver is arranged to feed the segment diagnostics signal in a high diagnostics voltage state to each of the segment electrodes. The diagnostic arrangement is configured to detect the fault in at least one of the segment electrodes based on the common connection current from the common connection to the reference voltage node, the fault being a short circuit fault, such that

- the fault in at least one of the electrodes is determined by a voltage of the low controlling node sinking below the switching voltage due to a voltage drop across the regulating resistor, the voltage drop being caused by the common connection current,

- the common connection current being caused by the short circuit fault such that the short circuit fault leads the segment diagnostics signal in a high diagnostics voltage state driven to each of the segment electrodes to the common connection,

- the voltage drop arranged to connect the emitter and the collector of the regulating NPN type BJT with a low resistance through the regulating NPN type BJT to sink the voltage of the low controlling node. This embodiment may be implemented easily to the conjunction of the common driver circuitry.

The short fault detection of the previous embodiment above is readily implemented to the low side of the half bridge, where a lower voltage node may be the ground node.

In an embodiment of the thin-film electroluminescent display, the low side switching element is an N-type field effect transistor with a low gate node as the low controlling node, a low drain node as the low first controlled node and a low source node as the low second controlled node. The NFET may be used in a so- called half-bridge circuit, and the short fault detection is readily implemented to the low side of the half-bridge circuit.

In an embodiment of the thin-film electroluminescent display, the low side switching element is an NPN type bipolar junction transistor (BJT) with a low base node as the low controlling node, a low collector node as the low first controlled node and a low emitter node as the low second controlled node. The BJT may also be used in a so-called half-bridge circuit, and the short fault detection is readily implemented to the low side of the half bridge, where a lower voltage node is usually the ground node.

As another aspect of the invention, a method for a detecting one or more faults in a thin-film electroluminescent display is disclosed. In the method, the thin- film electroluminescent display comprises

- a high voltage node supplying a driving voltage VH,

- a low voltage node supplying a low voltage VL,

- a high control voltage node supplying a high control voltage VC,

- a reference voltage node supplying a reference voltage VR,

- a thin-film display element extending substantially along a base plane defining a lateral extension of the thin-film display element.

The thin-film display element comprises

- a common layer comprising a common electrode,

- a segment layer comprising segment electrodes, the segment electrodes arranged at least partially to laterally overlap with the common electrode. The thin-film display element comprises

- a luminescent layer arranged between the common layer and the segment layer, the luminescent layer arranged to produce visible light when a voltage difference exceeding a threshold voltage VT is arranged between the common electrode and the overlapping segment electrodes.

The thin-film electroluminescent display comprises

- a segment driver arranged to feed a segment diagnostics signal to each of the segment electrodes, and

- a common driver comprising a common connection connected to the common electrode.

The thin-film electroluminescent display comprises a diagnostic arrangement comprising a diagnostic connection connected to the common connection. The method comprises the steps of:

- feeding the segment diagnostics signal to each of the segment electrodes by the segment driver,

- determining an electrical determinant of the common connection relative to the reference voltage node by the diagnostic arrangement, the electrical determinant being caused by the segment diagnostics signal, and

- detecting a fault in each of the segment electrodes by the diagnostic arrangement, the detecting based on the electrical determinant.

Advantage of the invention is that the method related to the TFEL display may determine a failed segment or non-failed (healthy) segment easily based on the electrical behaviour of the common electrode. Thus, the method for determining the health of a segment can be provided with no additional, separate diagnostics related interconnections to each of the segment electrodes.

In an embodiment of the method, the method aspect and its embodiments as defined above and in this text are executed in the thin-film electroluminescent display according to the thin-film electroluminescent display aspect of the invention and its embodiments as defined above and in this text.

An advantage of the invention is that the health (failed state or operative state) of each of the segment electrodes can be determined with e.g. preexisting driving signals (or segment diagnostics signals that may have a lower amplitude than segment driving signals for light production), segment drivers and segment interconnections between the driving electronics and the TFEL display panel (also called the TFEL display element), as the fault detection is performed based on the electrical behaviour of the common electrode. This is advantageous, as there is usually only one common electrode, and a plurality of segment electrodes, for example 20-100 segment electrodes for one segment TFEL display. This makes the interconnections and diagnostics considerably more simple.

The invention may also be used in a TFEL display with more than one common electrodes by performing the fault detection separately for each of the common electrodes and the segment electrodes overlapping each of the common electrodes.

For the purposes of this text, unless otherwise specified, a "connection" means an "electrical connection". Similarly, the word "connect" or "connected" means, unless otherwise specified, that the connected items are electrically connected with an intended, non-parasitic electrical connection. The connection may comprise one or more electrical components or elements, or be a "direct", galvanic connection.

For the purposes of this text, the concepts "voltage node" and "circuit node" are used interchangeably.

For the purposes of this text, both "TFEL" and "TFEL display" mean a "thin-film electroluminescent display".

For the purposes of this text, something occurring "during" a period of time means that something occurs within the period of time, but not necessarily from the start of the period of time, or till the end of the period of time, or from the start till the end of the period of time.

For the purposes of this text, a "high impedance state", a "floating state" or a "high Z" state mean the same thing, an electrical structure, for example an electrode like a common electrode which is not driven actively to a certain voltage with for example a common driving voltage signal, or connected otherwise to a predetermined voltage, e.g. to a ground voltage.

For the purposes of this text, a layer A "on" another layer B does not require that the layers A and B touch each other. In other words, layer A on layer B does not require that layers A and B are "directly" "on" each other.

For the purposes of this text, a "transparent" unit, for example a "transparent" display, a transparent TFEL or a "transparent" layer means that the human sense of sight is able to discern visual information behind the transparent unit such that the unit would block the visual information if the unit would not be transparent. No physical entity is 100% transparent owing to the electromagnetic wave nature of light in physical media and wave behaviour in media interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail by means of specific embodiments with reference to the enclosed drawings, in which

Figures 1 and 2 show schematically details of a TFEL display according to an embodiment of the invention,

Figures 3 - 5 show schematically electrical characteristics of an operating (healthy) segment, and failed (non-operating) segments,

Figures 6 - 7 show embodiments of the invention,

Figures 8 - 9 show embodiments of the invention related to detecting an open-circuit type of failure,

Figures 10 - 11 show embodiments of the invention related to detecting a short-circuit type of failure,

Figure 12 shows an embodiment of the invention related to detecting a short-circuit type of failure based on current detection,

Figures 13a -13c show embodiments related to switching circuits in current based failure detection, and

Figure 14 shows an embodiment of the method aspect of the current invention.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following description and in the associated Figures, like numbers (for example 70) and like labels (for example 91b) denote like elements.

Figures 1 and 2 show schematically a thin-film electroluminescent display 1 according to the invention. Figure 1 shows a projection from above the display 1, and Figure 2 a cutting plane projection through the common electrode 81 of the thin-film display element 80.

The TFEL display comprises a thin-film display element 80 extending substantially along a base plane 24 defining a lateral extension of the thin-film display element 80. The thin-film display element 80 comprises a common layer 23C that comprises a common electrode 81. In other words, the common layer 23C is patterned to comprise a common electrode 81 and electrically conductive traces or interconnections that connect the common electrode to a contact area of the thin-film display element 80 (contact area not shown).

Common electrode 81 may be fabricated for example with sputtering some conductive, yet transparent material like indium doped tin oxide ("ITO") or other such transparent, yet electrically conductive oxide or other such chemical compound on a substrate 20.

The thin-film display element 80 may also comprise a substrate 20, which may comprise transparent material like soda lime glass, aluminium silicate glass, or some transparent ceramic material, or an organic transparent material withstanding high process temperatures during the thin-film deposition processes.

The common layer 23C may be patterned for example by lithography and etching.

There may also be additional layers between the common layer 23C and the substrate 20, for example a thin aluminium oxide (A12O3) layer with a thickness of lOnm - 50nm (nanometres) for blocking leaching of ions like sodium ions from the substrate 20, deposited, for example, with an atomic layer deposition ("ALD") method.

The thin-film display element 80 comprises also a segment layer 23S comprising segment electrodes 91a, 91b, 91c, 91d, the segment electrodes 91a, 91b arranged at least partially to laterally overlap (overlap show with labels 97a, 97b) with the common electrode 81.

The segment layer 23S may be fabricated similarly to the common layer 23C, e.g. by sputtering ITO.

Both layers 23S and 23C may have a thickness of for example 200nm - 800nm. The thicker the layers 23C and 23S are, the more conducting the electrodes and interconnecting traces are, but the less transparent and optically clear the layer also is.

The TFEL display 1 may be readily also arranged such that the segment layer 23S is deposited or otherwise arranged closer to the substrate 20 than the common layer 23C.

The segment layer 23S is also patterned to comprise the segment electrodes 91a, 91b, 91c, 91d, and the interconnecting traces.

The segment layer 23S may also be patterned for example by lithography and etching.

If both the segment layer 23S and the common layer 23C are transparent (for example arranged of ITO or other such transparent, yet electrically conductive material), the TFEL display element 80 is transparent, as the other layers (22S, 22C and 21, and the substrate 20) are also transparent.

Thus, the TFEL display element 80 may be transparent.

The thin-film display element 80 comprises further a luminescent layer 21 arranged between the common layer 23C and the segment layer 23S. The luminescent layer 21 produces visible light when a voltage difference exceeding a threshold voltage VT is arranged between the common electrode 81 and the overlapping segment electrodes 91a, 91b, 91c, 9 Id.

A typical threshold voltage VT is 140V for a TFEL display with a driving voltage amplitude VH of 195V.

The luminescent layer 21 may be readily fabricated with the atomic layer deposition (ALD) method.

The luminescent layer 21 may comprise for example manganese doped zinc sulphide (ZnS:Mn) or terbium doped zinc sulphide (ZnS:Tb) for primarily yellow or green light output, respectively.

Thickness of the luminescent layer may be, for example, lOOnm - 2000nm, more preferably 200nm - lOOOnm or most preferably 400nm - 900nm.

The thin-film electroluminescent display 1 comprises also a segment driver 70 arranged to feed a segment diagnostics signal 191d, 192d, 193d, 194d to each of the segment electrodes 91a, 91b, 91a, 91b, and a common driver 50 comprising a common connection 85 connected to the common electrode 81.

For light output, the common driver 50 is arranged to feed a common driving voltage signal 189 to the common electrode 81 through the common connection 85.

To supply different voltages, the TFEL display 1 comprises a high voltage node 18 for supplying a driving voltage VH.

The driving voltage VH may be for example 195V or a voltage between 180V and 205V. One high voltage node 18 may be arranged in conjunction with the common driver 50.

The threshold voltage VT may be 135V - 145V.

The TFEL display 1 also comprises a low voltage node 17 supplying a low voltage VL.

The low voltage VL may be a zero voltage. One or more low voltage nodes 17 may be also arranged in conjunction with the common driver 50.

The driving voltage VH may be 75V - 85V, for example 80V. In this case, the threshold voltage VT may be 50V - 60V, for example 55V.

The low voltage VL of the low voltage node 17 may be zero volts.

The low voltage VL of the low voltage node 17 may be the ground voltage level of the common driver 50.

The thin-film electroluminescent display 1 comprises also a high control voltage node 19 supplying a high control voltage VC. The high control voltage VC may be the high voltage or supply voltage of the control electronics unit 40, e.g. the electrical voltage level representing digital 1 or logical 1 in the control electronics, e.g. 12V, 5V or 3V.

The thin-film electroluminescent display 1 comprises also a reference voltage node 16 supplying a reference voltage VR. The reference voltage node 16 may have any voltage level against which a voltage 85v of the common electrode 81 (or the associated common connection 85) maybe determined for segment fault detection purposes, or to which a current 85i from the common electrode 81 (or from the associated common connection 85) is flowing, for segment fault detection purposes.

The reference voltage VR may be the low voltage VL, or a ground or GND voltage, that is, a zero voltage.

The thin-film electroluminescent display comprises a diagnostic arrangement 60. The diagnostic arrangement 60 comprises a diagnostic connection 160 connected to the common connection 85.

The diagnostic arrangement 60 is configured to determine an electrical determinant 85d of the common connection 85 relative to the reference voltage node 16. The electrical determinant 85d is caused by the segment diagnostics signal 191d, 192d.

The electrical determinant 85d may be based on the voltage 85v of the common connection 85 relative to the reference voltage node 16.

The electrical determinant 85d may be based on current 85i through the common connection 85, from the common connection 85 to the reference voltage node 16.

In other words, the electrical determinant may be based on the voltage of the common electrode 81, or based on current to or from the common electrode 81.

The segment driver 70 is arranged to feed the segment diagnostics signal 191d, 192d, 193d, 194d to each of the segment electrodes 91a, 91b, 91c, 91d.

The diagnostic arrangement 60 is configured to detect a fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the electrical determinant 85d.

Thus, the fault detection of a segment electrode is performed from the side of the common electrode 81. As there are considerably more segment electrodes in a typical segment TFEL display than common electrodes, this makes the fault detection interconnections considerably more simple. It is also possible to use the existing driving electronics for segments for generating the segment diagnostics signals 19 Id, 192d.

The diagnostic arrangement 60 may be configured to detect a fault 91af in one or more of the segment electrodes 91a, 91b, 91c, 91d based on the electrical determinant 85d.

The segment diagnostics signal 19 Id, 192d may be a signal that has an amplitude which is sufficient to turn the segment on or off, that is, to produce light or not to produce light.

The segment diagnostics signals 19 Id, 192d may be fed to the segment electrodes 91a, 91b through segment connections 95a, 95b, 95c, 95d.

Each of the segment diagnostics signals 19 Id, 192d may comprise voltage pulses that alternate between the driving voltage VH and the low voltage VL.

Thus, the segment diagnostics signal 19 Id, 192d may be a signal that has an amplitude which is sufficient to turn the segment on or off, that is, to produce light or not to produce light.

Each of the segment diagnostics signals 19 Id, 192d may comprise voltage pulses that alternate between the control voltage VC and the low voltage VL.

Thus, the segment diagnostics signal 19 Id, 192d may also be a signal that has an amplitude which is not sufficient to turn the segment on or off, that is, to produce light or not to produce light. However, the amplitude of each of the segment diagnostics signals 19 Id, 192d is sufficient for fault detection.

The low voltage VL may be a zero voltage or a ground (GND) voltage. For light output, the common driving voltage signal 189 comprises pulses that alternate between the driving voltage VH and the low voltage VL. The low voltage VL may be a zero voltage or a ground voltage.

Thus, for light output, an alternating voltage, with alternating polarity is arranged between each of the segment electrodes 9 la-9 Id, and the common electrode 81.

When the segment diagnostics signal 191d, 192d is fed to each of the segment electrodes 91a, 91b, 91c, 91d, one or more of the segment electrodes 91a, 91b, 91c, 9 Id at any moment of time may be fed with the segment diagnostics signal 191d, 192d.

The segment driver 70 may be also arranged to feed the segment diagnostics signal 191d, 192d to each of the segment electrodes 91a, 91b, 91c, 91d sequentially. When the segment diagnostics signal 191d, 192d is fed to each of the segment electrodes 91a, 91b, 91c, 91d sequentially, only one segment electrode 91a, 91b, 91c, 9 Id at any moment of time is fed with the segment diagnostics signal 191d, 192d.

The segment connections 95a and 95b may comprise interconnections from the segment driver 70 and interconnections (like connection area or pad area) to the thin-film display element 80, conductors between the segment driver 70 and the thin-film display element 80, and traces on the segment layer 23S to the segment electrodes 91a, 91b.

As already presented, to drive the common electrode 81 for light output, the TFEL display 1 comprises also a common driver 50 comprising a common connection 85, the common connection 85 connected to the common electrode 81. Connection to the common electrode 81 may also comprise conductors, interconnecting elements and traces on the common layer 23C.

For the purposes of light production, the common driver 50 is arranged to feed a common driving voltage signal 189 to a common electrode 81 through the common connection 85.

To arrange the common driving voltage signal 189, the common driver 50 may comprise switches 51s, 51g that connect the common connection 85 to the high voltage node 18, or to the low voltage node 17 to drive the common electrode 81 to a driven state. Thus, in a driven state, the common electrode 81 has a distinct voltage set by the common driver 50.

As discussed above, for light production, in the driven state, the voltage of the common electrode 81 may alternate between the high voltage VH and the low voltage VL as driven by the common voltage driving signal.

To leave the common connection 85 and the corresponding undriven common electrode 81 to a high impedance state (that is, a floating state, undriven state or high-Z state), both switches 51s and 51g may be arranged into a nonconducting or open state.

In the high impedance state, the voltage of the common electrode 81 is determined on the charge remaining in the common electrode 81 from previous electrical activity of the common electrode 81, or from capacitive coupling from other charge carrying units of the display, mainly the segment electrodes 91a, 91b, 91c, and 91d.

Referring to Figure 2, the thin-film display element 80 may further comprise a first dielectric layer 22C on a first side of the luminescent layer 21, and a second dielectric layer 22S on a second side of the luminescent layer 21, the first dielectric layer 22C, the second dielectric layer 22S and the luminescent layer 21 arranged between the common layer 23C and the segment layer 23S. Purpose of the dielectric layers 22C and 22S is to provide electrical insulation and limit the current flowing between segment electrodes and the common electrode, that is, from the segment electrodes to the common electrode, or from the common electrode to the segment electrodes.

The first and second dielectric layers 22C and 22S may comprise for example a nanolaminate of aluminium and titanium oxides, and their thickness may be for example lOOnm - 300nm each.

Clearly, in terms of electrical circuit theory, an overlapping pair of one segment electrode and one common electrode is essentially a "parallel plate capacitor", with said overlapping areas of the electrodes being the capacitor plates, and the luminescent layer and potential dielectric layers as the insulating material between the plates. The capacitance C of such a parallel plate capacitor is determined by the separation s of the plates, area of the plates (that is, the area of the segment/common electrode overlap) A and effective permittivity EEFF of the insulating material between the segment layer 23S and common layer 23C according to formula C = EEFF A/S.

As in Figure 1, the TFEL display 1 may also comprise a power unit 42 arranged to feed energy for the various operations of the display. The power unit 42 may comprise transformers to provide different voltage levels needed for the operation for the display 1, for example the voltages VH, VL, VC and VR.

The TFEL display 1 may comprise also control unit 40 arranged to command the common driver 50 and the segment driver 70 to produce correct common driving voltage signals 189, and segment diagnostics signals 191d ,192d, 193d, 194d, respectively. The control unit 40 may operate based on information received from an interface 43. Interface 43 may be, for example, an SP1 interface, an 12C interface, or a CANBus interface.

The control unit 40 may also control the operations of the diagnostic arrangement 60 such that the diagnostic determination on the health of the segment electrodes 91a - 91d is timed properly, and the rest of the TFEL display 1 is set to a state that enables the diagnostic determination.

The control electronic unit 40 may comprise a micro controller, a microprocessor, a memory or an FPGA chip, or any combination thereof.

The diagnostic arrangement 60 may comprise a micro controller, a microprocessor, a memory or an FPGA chip, or any combination thereof.

Functionality of the common driver 50 and the segment driver 70 may also combined into or provided with a commercially available integrated circuit, for example the HV7224 chip available from Supertex Inc. or Microchip Inc. The HV7224 chip is a 40-channel serial to parallel converter with a high voltage backplane driver and push-pull outputs capable of 200V, 40 channel output. Several HV7224 chips can be cascaded for the output of over 40 channels. Herein, one channel means one segment electrode / common electrode pair.

Functionality of the common driver 50 or the segment driver 70, or both the common driver 50 and the segment driver 70, may be also realized with discrete electronics components.

Light production and segment electrode diagnostics may be interleaved in time such that when the luminescent layer 21 at the areas of overlap of each of the segment electrodes 91a - 91d and the common electrode 81 produce light, diagnostics is not performed, in other words, diagnostic arrangement 60 does not measure or determine the electrical determinant 85d. Similarly, when the diagnostic arrangement 60 determines the electrical determinant 85d, light is not produced.

By arranging the interleaving with short intervals (e.g. performing the determination of the electrical determinant 85d in some milliseconds between two periods of light output), human sense of sight perceives the light output as continuous light output.

Figure 3 illustrates a healthy, functioning segment electrode 91a next to another functioning segment electrode 91b. The segment electrode 91 is driven through a segment connection 95a, and the common electrode 81 with a common connection 85. Units like 23S, 23C, 22S, 22C and 21 correspond to those of Figure 2.

An equivalent circuit of a healthy segment electrode-common electrode pair 91a-81 is a capacitor 45c.

As shown in Figure 4, as a fault 91af, an open circuit fault 91fo turns the segment electrode 91a (or the underlying common electrode 81 at an area of the overlapping 97a segment electrode 91a, overlap as in Figure 2) into a non- conductive patch, destroying the capacitive nature of the segment electrode. Thus, a mere end in the segment connection 95a may be generated through an open circuit fault 91fo, having an open circuit 45o as the equivalent circuit. For example, the segment electrode 91a may burn and thus oxidise and lose its electrically conductive capacity. Units like 23S, 23C, 22S, 22C and 21 correspond to those of Figure 2.

Turning to Figure 5, as a fault 91af, a short circuit fault 91fs turns the thin film stack between the segment and common electrodes electrically conductive through some electrical breakdown that, for example, forces the common and segment electrodes on layers 23C and 23S to mechanically adjoin, as each of the thin films may be only some 100s of nanometers thin between said layers. Thus, a short circuit or a low-impedance connection is generated by a short circuit fault 91fs, having a short circuit 45s as an equivalent circuit, with a conductive circuit path 45cp between said layers. Again, other units like 23S, 23C, 22S, 22C and 21 correspond to those of Figure 2.

In an embodiment and turning next to Figure 6 in addition to Figure 1, in the thin-film electroluminescent display 1, the common driver 50 is arranged to set the common connection 85 to a high impedance state, and the electrical determinant 85d comprises a common connection voltage 85v of the common connection 85 relative to the reference voltage node 16.

In other words, health of each of the segment electrodes 91a - 9 Id is determined based on the voltage of the common connection 85 (which is connected to the common electrode 81), and by sensing the voltage 85v of the common electrode 81, the voltage caused by the segment diagnostics signals 19 Id, 192d. The determination of the common connection voltage 85v may be done relative to the arbitrary reference voltage in the reference voltage node 16.

In an embodiment, and still referring to Figure 6, the common driver 50 is arranged to set the common connection 85 to a high impedance state, and the electrical determinant 85d comprises a common connection voltage 85v of the common connection 85 relative to reference voltage node 16 such that the reference voltage node 16 is the low voltage node 17. This embodiment is similar to the previous embodiment, but the reference voltage against which the voltage is sensed is the low voltage VL of the low voltage node 17.

In an embodiment, and still referring to Figure 6, the common driver 50 is arranged to set the common connection 85 to a high impedance state, and the electrical determinant 85d comprises a common connection voltage 85v of the common connection 85 relative to reference voltage node 16 such that the reference voltage node 16 is a ground node with a zero voltage. This embodiment is again similar to the previous embodiment, but the reference voltage against which the voltage is sensed is the ground or zero voltage.

In determining if the segment electrode 91a - 91d has a fault, the thin- film electroluminescent display 1 may also determine if the segment electrode 91a - 9 Id does not have a fault, in other words, is operating.

In other words, in determining if the segment electrode 91a - 9 Id has a fault, the thin-film electroluminescent display 1 may determine if the segment electrode 91a - 9 Id has a fault or not.

Thus, fault of the segment electrode is indicated by a state of the segment electrode where the segment electrode is non-operating.

A fault in the segment electrode 91a - 9 Id indicates that the segment electrode has failed, is not operative and is not "healthy".

An operating segment electrode 91a - 91d indicates that the segment electrode has not failed, is operative and is "healthy".

Turning next to Figure 8, in an embodiment, in the thin-film electroluminescent display 1, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 19 Id, 192d in a high diagnostics voltage state 191h, 192hto each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state 1811 of the common connection voltage 85v.

In other words, if the segment electrode 91a has failed to an open circuit fault 91fo, as shown in Figure 4, the voltage of the high diagnostics voltage state 191h, 192h does not reach the common electrode 81 and the associated common connection 85, and thus a fault may be determined.

In the high diagnostics voltage state 191h, 192h, the segment diagnostics signal 19 Id, 192d may have, at a time point of the high diagnostics voltage state 19 lh, 192h, the amplitude value of the segment diagnostics signal 191d, 192d.

Turning still to Figure 8, in an embodiment, in the thin-film electroluminescent display 1, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 19 Id, 192d in a high diagnostics voltage state 191h, 192hto each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo, such that an operating segment electrode 91a, 91b, 91c, 91d is determined by a high control voltage state 181h of the common connection voltage 85v, the operating segment electrode 91a, 91b, 91c, 91d being one of the segment electrodes 91a, 91b, 91c, 91d.

In the high control voltage state 18 lh, the common connection voltage 85v is such that it causes a logical high state in the diagnostic arrangement 60.

The diagnostic arrangement 60 may also comprise a sensing unit 62 comprising an input node 62i, and a series resistor 61 that connects the input node 62i to diagnostic connection 160, which is connected to the common connection 85.

In the high control voltage state 18 lh, the common connection voltage 85v is such that it causes a logical high state in the input node 62i of the sensing unit 62 of the diagnostic arrangement 60 through the series resistor 61.

In other words, in the high control voltage state 181h, the common connection voltage 85v is such that it may be interpreted as a logical high state by the diagnostic arrangement 60.

In the low control voltage state 1811, the common connection voltage 85v may be equal or close to being equal to the low voltage VL.

In other words, in the low control voltage state 1811, the common connection voltage 85v is such that it may be interpreted as a logical low state by the diagnostic arrangement 60.

The low voltage VL may be a zero or ground voltage.

If the segment electrode 91a has not failed to an open circuit fault 91fo, as shown in Figure 4, the voltage of the high diagnostics voltage state 19 lh, 192h reaches the common electrode 81 and the associated common connection 85 capacitively, and thus an operating segment or such a state may be determined.

Turning still to Figure 8, in an embodiment, in the thin-film electroluminescent display 1, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 19 Id, 192d in a high diagnostics voltage state 191h, 192hto each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state 1811 of the common connection voltage 85v, and an operating segment electrode 91a, 91b, 91c, 91d is determined by a high control voltage state 181h of the common connection voltage 85v, the operating segment electrode 91a, 91b, 91c, 91d being one of the segment electrodes 91a, 91b, 91c, 91d.

In other words, the thin-film electroluminescent display 1 may also make a determination if the segment has a fault, and if the segment does not have a fault as described above.

As shown in Figures 8-11, the diagnostic arrangement 60 may also comprise a sensing unit 62, comprising an input node 62i, and a series resistor 61 that connects the input node 62i to diagnostic connection 160, which is connected to the common connection 85.

The series resistor 61 may drop the voltage sensed by the sensing unit 62 at the input node 62 i from a driving voltage level (e.g. amplitude VH) to a control voltage level (e.g. to a signal with amplitude VC).

As shown in Figures 8-11, the sensing unit 62 may be e.g. a microcontroller or a microprocessor comprising instructions to perform the measurement of the common connection voltage 85v.

Related to Figures 8-11, the input node 62i may be e.g. a GP1O (general purpose input output) node of the sensing unit 62.

Turning next to Figure 9, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v.

In the low diagnostics voltage state 1911, 1921, the segment diagnostics signal 19 Id, 192d is set to the low voltage VL as voltage value.

The stationary high control voltage state 181h may be a state where the voltage remains substantially the same for the duration of the determination of the voltage 85v of the common connection 85.

The stationary high control voltage state 181h may be a state where the voltage remains within 10% of the detected value for the duration of the determination of the voltage 85v of the common connection 85.

In other words, if the segment electrode 91fo has no connection (that is, the fault of the segment electrode is an open circuit fault) to the common electrode 81, the pull-up-resistor 61pu keeps the voltage of the diagnostic connection 160 in a high control voltage state 181h, and a fault 91af of an open circuit kind 91of may be detected.

Turning still to Figure 9, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo such that an operating segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state 1811 of the common connection voltage 85v rising to a high control voltage state 181h due to the pull- up resistor 61pu charging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 9 Id being one of the segment electrodes 91a, 91b, 91c, 91d.

In the high control voltage state 18 lh, the common connection voltage 85v is such that it causes a logical high state in the input node 62i of the sensing unit 62 of the diagnostic arrangement 60 through the series resistor 61.

In other words, in the high control voltage state 181h, the common connection voltage 85v is such that it may be interpreted as a logical high state by the diagnostic arrangement 60.

In the low control voltage state 1811, the common connection voltage 85v may be equal or close to being equal of the low voltage VL.

In other words, in the low control voltage state 1811, the common connection voltage 85v is such that it may be interpreted as a logical low state.

The low voltage VL may be a zero or ground voltage.

In other words, if the segment electrode is healthy (that is, operating), it acts like a capacitor that gets charged by current flowing through the pull-up resistor 61pu, as the segment electrode is fed with a signal in a low diagnostics voltage state 1911.

Turning still to Figure 9, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being an open circuit fault 91fo, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v, and an operating segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state 1811 of the common connection voltage 85v rising to a high control voltage state 181h due to the pull- up resistor 61pu charging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 91d being one of the segment electrodes 91a, 91b, 91c, 91d.

In other words, the thin-film electroluminescent display 1 may also make a determination if the segment has a fault, and if the segment does not have a fault as described above.

In an embodiment, if the diagnostic arrangement 60 detects a fault 91af in any of the segment electrodes 91a-91d, it may shut down the operation of the TFEL display 1.

In an embodiment, if the diagnostic arrangement 60 detects a fault or faults 91af in one or more faulty segment electrodes 9 la-9 Id, the TFEL display 1 may stop producing light from the one or more faulty segment electrodes 91a-91d. Turning next to Figure 10, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pulldown resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v caused by the segment diagnostics signal 19 Id, 192d in the high diagnostics voltage state 19 lh, 192h short-circuited to the common electrode 81.

Thus, a diagnostic signal in a high diagnostics voltage state 191h, 192h leaking through a short-circuit 91fs from any of the segment electrodes 91a, 91b, 91c, 9 Id maybe detected, indicating that at least one of the segment electrodes has faulted through a short circuit.

Turning still to Figure 10, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pulldown resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that a state where all segment electrodes 91a, 91b, 91c, 91d are operating is determined by a high control voltage state of the common connection voltage 85v decaying to a low control voltage state 1811 due to the pulldown resistor 61pd discharging segment capacitors 45c comprising the common electrode 81 and the segment electrodes 91a, 91b, 91c, 91d.

Thus, if none of the segment electrodes 91a, 91b, 91c, 91d are faulted through a short-circuit to the common electrode 81, the segment electrodes act with the common electrode like a parallel connection of capacitors, which, in turn, may be detected through the discharging voltage behaviour.

Turning still to Figure 10, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull- down resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v caused by the segment diagnostics signal 19 Id, 192d in the high diagnostics voltage state 19 lh, 192h short-circuited to the common electrode 81, and a state where all segment electrodes 91a, 91b, 91c, 91d are operating is determined by a high control voltage state 181h of the common connection voltage 85v decaying to a low control voltage state 1811 due to the pulldown resistor 61pd discharging segment capacitors 45c comprising the common electrode 81 and the segment electrodes 91a, 91b, 91c, 91d.

Turning still to Figure 10, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pulldown resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v caused by the segment diagnostics signal 191d, 192d in the high diagnostics voltage state 191h, 192h short-circuited to the common electrode 81.

By feeding the segment diagnostics signal sequentially, it is possible to determine which of the segment electrodes 91a - 9 Id has faulted.

Turning still to Figure 10, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pulldown resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that an operating segment electrode 91a, 91b, 91c, 9 Id is determined by a high control voltage state 181h of the common connection voltage 85v decaying to a low control voltage state 1811 due to the pull-down resistor 61pd discharging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 9 Id being one of the segment electrodes 91a, 91b, 91c, 91d.

In the high control voltage state 18 lh, the common connection voltage 85v is such that it causes a logical high state in the input node 62i of the sensing unit 62 of the diagnostic arrangement 60 through the series resistor 61.

In other words, in the high control voltage state 181h, the common connection voltage 85v is such that it may be interpreted as a logical high state by the diagnostic arrangement 60.

In the low control voltage state 1811, the common connection voltage 85v may be equal or close to being equal of the low voltage VL.

In other words, in the low control voltage state 1811, the common connection voltage 85v is such that it may be interpreted as a logical low state.

The low voltage VL may be a zero or ground voltage.

Turning still to Figure 10, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pulldown resistor 61pd configured to pull the diagnostic connection 160 towards the low voltage VL. The segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in the segment electrode 91a, 91b, 91c, 91d is determined by a stationary high control voltage state 181h of the common connection voltage 85v caused by the segment diagnostics signal 191d, 192d in the high diagnostics voltage state 191h, 192h short-circuited to the common electrode 81, and an operating segment electrode 91a, 91b, 91c, 91d is determined by a high control voltage state 18 lh of the common connection voltage 85v decaying to a low control voltage state 1811 due to the pull-down resistor 61pd discharging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 91d being one of the segment electrodes 91a, 91b, 91c, 91d.

In other words, the thin-film electroluminescent display 1 may also make a determination by sequential driving of the segment diagnostics signal 191d, 192d to each of the segment electrodes 91a, 91b, 91c, 91d, if each of the segments has a fault, and if the segment does not have a fault, as described above.

Turning next to Figure 11, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to feed the segment diagnostics signal 19 Id, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d. The diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 91d is determined by a stationary low control voltage state 1811 of the common connection voltage 85v caused by the segment diagnostics signal 19 Id, 192d in the low diagnostics voltage state 1911, 1921 short-circuited to the common electrode 81.

In other words, a short-circuit in any of the segment electrodes drives the common electrode to a low control voltage state 1811, indicating a fault amongst the segment electrodes.

The stationary low control voltage state 1811 may be a state where the voltage remains substantially the same for the duration of the determination of the voltage 85v of the common connection 85.

The stationary low control voltage state 1811 may be a state where the voltage remains within 10% of the detected value for the duration of the determination of the voltage 85v of the common connection 85.

Turning still to Figure 11, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to feed the segment diagnostics signal 19 Id, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that a state where all segment electrodes 91a, 91b, 91c, 91d are operating is determined by a low control voltage state of the common connection voltage 85v rising to a high control voltage state 181h due to the pull- up resistor 61pu charging segment capacitors 45c comprising the common electrode 81 and the segment electrodes 91a, 91b, 91c, 91d.

In other words, in case none of the segment electrodes are short- circuited to the common electrode, the segment electrodes-common electrode combination in parallel are pulled up by the pull-up-resistor 61pu, which may then be detected.

Turning still to Figure 11, in an embodiment of the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC. The segment driver 70 is arranged to feed the segment diagnostics signal 19 Id, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 91d is determined by a stationary low control voltage state 1811 of the common connection voltage 85v caused by the segment diagnostics signal 19 Id, 192d in the low diagnostics voltage state 1911, 1921 short-circuited to the common electrode 81, and a state where all segment electrodes 91a, 91b, 91c, 91d are operating is determined by a low control voltage state 1811 of the common connection voltage 85v rising to a high control voltage state 181h due to the pull- up resistor 61pu charging segment capacitors 45c comprising the common electrode 81 and the segment electrodes 91a, 91b, 91c, 91d.

Thus, diagnostics of at least one faulted segment electrode due to short circuit can be combined with a diagnostics that all segment electrodes are functioning or healthy.

Turning still to Figure 11, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in the segment electrode 91a, 91b, 91c, 9 Id is determined by a stationary low control voltage state 1811 of the common connection voltage 85v caused by the segment diagnostics signal 191d, 192d in the low diagnostics voltage state 1911, 1921 short- circuited to the common electrode 81.

In other words, through the short circuit fault 91fs, a low diagnostics voltage state 1911 reaches the diagnostic connection and keeps the voltage of the diagnostic connection 160 in a low diagnostics voltage state 1911, 1921 for each of the faulted segment electrodes.

Turning still to Figure 11, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that an operating segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state 1811 of the common connection voltage 85v rising to a high control voltage state 18 lh due to the pull-up resistor 61pu charging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 91d being one of the segment electrodes 91a, 91b, 91c, 9 Id.

In the high control voltage state 18 lh, the common connection voltage 85v is such that it causes a logical high state in the input node 62i of the sensing unit 62 of the diagnostic arrangement 60 through the series resistor 61.

In other words, in the high control voltage state 181h, the common connection voltage 85v is such that it may be interpreted as a logical high state by the diagnostic arrangement 60.

In the low control voltage state 1811, the common connection voltage 85v may be equal or close to being equal of the low voltage VL.

In other words, in the low control voltage state 1811, the common connection voltage 85v is such that it may be interpreted as a logical low state by the diagnostic arrangement 60. The low voltage VL may be a zero or ground voltage.

In other words, for a healthy segment electrode 91a-91d, the pull-up resistor 61pu can charge the segment electrode-common electrode pair and pull up the common electrode 81 and the associated common connection 85, as the common electrode 81 is not kept in a low state by a short circuit 91fs indicative of a fault. In this embodiment the segment electrode 91a-91d is in a low diagnostics voltage state 1911, 1921.

Turning still to Figure 11, in an embodiment, in the thin-film electroluminescent display 1, the diagnostic arrangement 60 comprises a pull-up resistor 61pu configured to pull the diagnostic connection 160 towards the high control voltage VC, the segment driver 70 is arranged to sequentially feed the segment diagnostics signal 191d, 192d in a low diagnostics voltage state 1911, 1921 to each of the segment electrodes 91a, 91b, 91c, 91d, and the diagnostic arrangement 60 is configured to detect the fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d based on the voltage 85v of the common connection 85, the fault 91af being a short circuit fault 91fs, such that the fault 91af in the segment electrode 91a, 91b, 91c, 9 Id is determined by a stationary low control voltage state 1811 of the common connection voltage 85v caused by the segment diagnostics signal 191d, 192d in the low diagnostics voltage state 1911, 1921 short- circuited to the common electrode 81, and an operating segment electrode 91a, 91b, 91c, 91d is determined by a low control voltage state of the common connection voltage 85v rising to a high control voltage state 181h due to the pull- up resistor 61pu charging a segment capacitor 45c comprising the common electrode 81 and the operating segment electrode 91a, 91b, 91c, 91d, the operating segment electrode 91a, 91b, 91c, 9 Id being one of the segment electrodes 91a, 91b, 91c, 91d.

In other words, the thin-film electroluminescent display 1 may also make a determination if the segment has a fault, and if the segment does not have a fault, as described above.

Turning back to Figure 7, in an embodiment of the thin-film electroluminescent display 1, the electrical determinant 85d comprises a common connection current 85i between the common connection 85 and the reference voltage node 16. This embodiment is advantageous in determining a short circuit type of fault 91fs (as shown in Figure 5).

In other words, a fault in each of the segment electrodes 9 la-9 Id may also be determined by a current flowing from the common electrode 81 and the associated common connection 85 to the reference voltage node 16.

Turning still to Figure 7 , in an embodiment of the thin-film electroluminescent display 1, the electrical determinant 85d comprises a common connection current 85i between the common connection 85 and the reference voltage node 16 such that the reference voltage node 16 is the low voltage node 17. This embodiment is advantageous in determining a short circuit type of fault 91fs (as shown in Figure 5).

Turning still to Figure 7 , in an embodiment of the thin-film electroluminescent display 1, the electrical determinant 85d comprises a common connection current 85i between the common connection 85 and the reference voltage node 16 such that the reference voltage node 16 is a ground node with a zero voltage. This embodiment is advantageous in determining a short circuit type of fault 91fs (as again shown in Figure 5).

In other words, a fault in each of the segment electrodes 9 la-9 Id may also be determined by a current flowing from the common electrode 81 and the associated common connection 85 to a ground node.

Referring next to Figures 12 and 13a, in an embodiment of the thin-film electroluminescent display 1, the common driver 50 comprises a low side switching element 132.

The low side switching element 132 is shown with a symbol of an NFET in Figure 12, but the low side switching element 132 is a general switching element 132 as shown in Figure 13a.

The low side switching element 132 comprises a low controlling node 132i, a low first controlled node 132oa connected to the common connection 85 through the diagnostic connection 160, and a low second controlled node 132ob.

The low side switching element 132 may connect the low first controlled node 132oa and the low second controlled node 132ob together with a low impedance connection or short-circuit like connection when a voltage equal to or higher than a switching voltage 32 is arranged to the low controlling node 132i.

In other words, the low side switching element 132 is arranged to connect the low first controlled node 132oa and the low second controlled node 132ob with a low-impedance connection when a voltage equal to or higher than a switching voltage 32 is connected to the low controlling node 132i.

The common driver 50 comprises also a regulating resistor 144, and a regulating NPN type 143 (bipolar junction transistor) 143. The regulating NPN type BJT comprises a base 143b connected to the low second controlled node 132ob, an emitter 143e connected to the reference voltage node 16, and a collector 143c connected to the low controlling node 132i. The regulating resistor 144 is connected between the low second controlled node 132ob and the reference voltage node 16.

The diagnostic arrangement 60 comprises a voltage sensing unit 63 arranged to sense the voltage of the low controlling node 132i.

The segment driver 70 is arranged to feed the segment diagnostics signal 191d, 192d in a high diagnostics voltage state 191h, 192h to each of the segment electrodes 91a, 91b, 91c, 91d.

The diagnostic arrangement 60 is configured to detect the fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 9 Id based on the common connection current 85i from the common connection 85 to the reference voltage node 16, the fault 91af being a short circuit fault 91fs. The fault 91af in at least one of the segment electrodes 91a, 91b, 91c, 91d is determined by a voltage of the low controlling node 132i sinking below the switching voltage 32 due to a voltage drop 144vd across the regulating resistor 144, the voltage drop 144vd being caused by the common connection current 85i.

The common connection current 85i is caused by the short circuit fault 91fs such that the short circuit fault 9 lfs leads the segment diagnostics signal 19 Id, 192d in a high diagnostics voltage state 191h, 192h driven to each of the segment electrodes 91a, 91b, 91c, 91d to the common connection 85.

The voltage drop 144vd is arranged to connect the emitter 143e and the collector 143c of the regulating NPN type BJT 143 with a low resistance through the regulating NPN type BJT 143 to sink the voltage of the low controlling node 132i.

Referring next to Figures 12, 13a and 13b, in an embodiment of the thin- film electroluminescent display 1, the low side switching element 132 is an N-type field effect transistor 133 (NFET) with a low gate node 133g as the low controlling node 132i, a low drain node 133d as the low first controlled node 132oa and a low source node 133s as the low second controlled node 132ob.

Referring next to Figures 12, 13a and 13c, in an embodiment of the thin- film electroluminescent display 1, the low side switching element 132 is an NPN type BJT 133 with a low base node 134b as the low controlling node 132i, a low collector node 134c as the low first controlled node 132oa and a low emitter node 134e as the low second controlled node 132ob.

The reference voltage node 16 may be the low voltage node 17, or a ground node with a zero voltage.

As shown in Figure 12, the voltage sensing unit 63 may comprise microcontroller or a microprocessor 63uc comprising instructions to perform the measurement of the low controlling node 132i.

The voltage sensing unit 63 may comprise a voltage sensing unit input node connected to the low controlling node 132i .

The voltage sensing unit input node may be e.g. a GP1O (general purpose input output).

The voltage sensing unit 63 may comprise a diode 63d to isolate any signals generated by the voltage sensing unit 63 from the rest of the common driver 50.

The voltage sensing unit 63 may comprise a voltage divider comprising two resistors 63a and 63b to adjust the voltage levels sensed by the voltage sensing unit 63 to a proper voltage level.

As another aspect of the present invention, and referring to Figure 14, a method 300 for a detecting one or more faults in a thin-film electroluminescent display 1 is disclosed. The thin-film electroluminescent display 1 comprises a high voltage node 18 supplying a driving voltage VH, a high control voltage node 19 supplying a high control voltage VC, and a reference voltage node 16 supplying a reference voltage VR.

The thin-film electroluminescent display 1 comprises also a thin-film display element 80 extending substantially along a base plane 24 defining a lateral extension of the thin-film display element 80. The thin-film display element 80 comprises

- a common layer 23C comprising a common electrode 81,

- a segment layer 23S comprising segment electrodes 91a, 91b, 91c, 9 Id, the segment electrodes 91a, 91b, 91c, 9 Id arranged at least partially to laterally overlap 97a, 97b with the common electrode 81, the thin-film display element 80 comprising

- a luminescent layer 21 arranged between the common layer 23C and the segment layer 23S, the luminescent layer 21 arranged to produce visible light 99a when a voltage difference exceeding a threshold voltage VT is arranged between the common electrode 81 and the overlapping 97a, 97b segment electrodes 91a, 91b, 91c, 9 Id.

The thin-film electroluminescent display 1 comprises also

- a segment driver 70 arranged to feed a segment diagnostics signal 191d, 192d to each of the segment electrodes 91a, 91b, 91c, 91d, and

- a common driver 50 comprising a common connection 85 connected to the common electrode 81.

The thin-film electroluminescent display 1 comprises a diagnostic arrangement 60 comprising a diagnostic connection 160 connected to the common connection 85. The method 300 comprises steps 310, 320 and 321 as follows:

Step 310: feeding the segment diagnostics signal 191d, 192d to each of the segment electrodes 91a, 91b, 91c, 91d by the segment driver 70.

Step 320: determining an electrical determinant 85d of the common connection 85 relative to the reference voltage node 16 by the diagnostic arrangement 60, the electrical determinant 85d being caused by the segment diagnostics signal 19 Id, 192d, and

Step 321: detecting a fault 91af in each of the segment electrodes 91a, 91b, 91c, 91d by the diagnostic arrangement 60, the detecting based on the electrical determinant 85d.

For units and labels not disclosed in Figure 14, units in Figures l-13c are referred to.

In an embodiment of the method 300, the method 300 is executed in the thin-film electroluminescent display 1 according to the thin-film electroluminescent display aspect and its embodiments as defined above.

The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the above examples but may vary within the scope of the claims.