Field of technology

The invention concerns method of load modulation during NFC communication between PCD device and PICC device. The invention describes an antenna system on the side of the PICC device which at small dimensions effectively influences the output of the antenna of the PCD device and it also discloses preferable arrangement of the controlling chip for control of the antenna system on the side of the PICC device.

Prior state of the art

With passive mode in NFC platform (for example, ISO/IEC 14443) the initializer/transmitter (PCD, for example card reader) provides a carrier field and an energy for the device of transponder/receiver (PICC, for example payment card), which responds with load modulation. Antenna of the receiver must by sufficiently effective in order to meet the energy demands of the receiver, which in this mode lacks - or does not need to have - its own power source / source of energy.

PCD readers usually have form of larger devices or they are part of larger devices which have sufficient space for placement of large NFC flat antenna with sufficient radiating power. Common PICC devices in form of payment cards have sufficiently large surface of the plastic carrier for placement of the flat antenna. After implementing PICC devices into more complex host devices, for example, into mobile phone, the available surface - or space - significantly diminishes, and the size of flat antenna decreases, too. A solenoid antenna, usually with ferrite core, is used instead of flat receiving antenna, when available surface diminishes.

Solutions are published with two antennas, for example WO2017109681 A1 , WO2018198082 A1 , which disclose two antennas - one solenoid with ferrite core and one spiral - or two solenoid antennas cooperating with flat, planar antenna; these solutions, however, only concern active modulation. In case of passive load modulation the problems with the stability of created NFC channel are usually solved by increase in the antenna’s dimensions or - if that is not possible - by increasing the power of PCD device. On the side of the PICC device it is not possible to independently increase the performance pursuant to physical essence of the passive position of the PICC device.

With reduction of sizes of flat spiral antennas a situation arises where the bond between PCD antennas and PICC device is not sufficiently strong. PICC antenna is not capable of changing the available magnetic field into sufficient amount of energy needed for correct operation of PICC device’s circuits and/or the change of amplitude on the PCD device, caused by modulation of load of the antenna system of PICC device, is so small that the inner circuits of PCD device cannot detect it or correctly read it. This leads to unreliable communication, or even to complete loss of communication between PCD and PICC devices.

A simple solution is desired and not known on the side of the PICC device, which will be capable of communicating with common PCD device whereby the antenna on the side of the PICC device will have small dimensions and sufficient effects upon the antenna of the PCD device.

Essence of the invention

The abovementioned deficiencies are significantly remedied by method of load modulation during communication between PICC and PCD device which changes the load modulation of the antenna on the side of the PICC device by means of switch controlled by the controlling unit pursuant to transferred data according to this invention which essence lies in the fact that individual switches of at least two antennas with their own resonant circuit are controlled independently by the control unit; the control of the switches is synchronized with identical data control, whereby the amount of load of individual antennas in the side of PICC device is different. The independent antennas on the side of PICC device are in such mutual spatial position that all have induction bonding with antenna of PCD device. In the most common arrangement two independent antennas will be used; in principle it is possible to use more antennas, too.

Arrangement with at least two antennas with independent level of load, while the synchronization of these changes is maintained, uses an inherent reserve of load modulation pursuant to the prior state of the art. In case of load modulation on the side of the antenna of PCD device, the changes are basically achieved by loading the antenna’s resonant circuit on the side of the PICC device. The level of loading must be chosen in such a way that the circuits on the side of the PICC device are not disconnected from the reception of the energy and from the basic excitation signal from the PCD device. This invention makes the use of physical boundaries of load modulation more effective by the fact that at least one antenna on the side of the PICC device is during modulation loaded only in such a degree that the output of this antenna still provides PICC device with sufficient energy intake and/or with basic excitation signal. The second antenna and other antennas of PICC device are loaded more, which causes them to influence output of antenna on the side of PCD device more.

In preferable arrangement with two antennas on the side of the PICC device the first antenna will be loaded only to such a degree that it allows the synchronization of the circuits of PICC device with circuits of PCD device, and the second antenna on the side of the PICC device will be loaded more.

The deficiencies in the prior state of the art are significantly remedied by the antenna system on the side of the PICC device itself, too, which includes first resonant circuit with first antenna which is connected to the PICC controller, where the first resonant circuit of the first antenna is switched by first switch which is connected with data output from the control unit of the PICC controller according to this invention which essence lies in the fact that it includes at least one further antenna on the second independent resonant circuit which is switch by a second switch, whereby the second switch is connected with the data output from the control unit of the PICC controller, whereby the first and second antenna are placed in mutual vicinity. The antennas themselves on the side of PICC device are in such mutual spatial position that all have induction bonding with antenna of PCD device. The mutual vicinity, nearness, of the multiple antennas on the side of the PICC device shall be understood in such a way that these antennas are commonly within reach of mutual inductance with the antenna of PCD device. The boundary of the common placement of the antennas on the side of the PICC device is delimited by the action zone of PCD device, which is usually defined by the size of the flat PCD antenna.

The term“controller” in this text means an element which is intended for modulation of the resonant circuit of the antenna on the side of the PICC device. This controller can also be called a“chip”, a“controlling element”, an “excitation element”, a“modulation element”.

The resonant circuit of the second antenna or multiple further antennas, respectively, will usually have different impedance parameters compared to resonant circuit of the first antenna; it is crucial, however, that the switch of the second antenna or multiple further antennas is adapted to higher load.

It is preferable of the antennas on the side of the PICC device are solenoid antennas. The term solenoid antenna in this file denotes a coil with multiple windings of the conductor on the core, for example on the core of the rectangular cross-section, where the length (longitudinal dimension) of the coil is more than its transversal dimension; usually the length of the coil is more than five times the diagonal of its cross-section (for example, in case of the rectangular cross-section of the core). The width of the core is its transversal dimension through which the core is projected onto the groundplan of the antenna’s carrier, that is, onto the plane of the base. In case of the oblong cross-section of the core the width of the core is a dimension in the direction parallel with the plane of the base; in case of the circular cross-section of the core the width of the core is its diameter. The core can be ferrite or from other material with similar magnetic features. The length of the solenoid antenna denotes a total length of the core or the length of the core covered by the conductor threads.

First and second solenoid antenna can have similar dimensions and similar constructions, but this is not necessary.

It is preferable if the first and second solenoid antenna are placed by each other, that is, in parallel with each other, where the gap between them is less than five times the width of the first and second solenoid antenna. The gap between the first and second antenna in case of their mutually parallel placement shall be less than 5 mm. A solution is functional, too, where the first and second solenoid antenna is placed in mutually perpendicular L-shaped or T-shaped position, pursuant to the available surface free on the PCB of the host device.

The second switch or multiple further switches can be part of the PICC controller, that is, they can be part of the integrated chip which is designed for control of multiple antennas pursuant to this invention. The invention’s subject- matter is also the chip itself as a hardware element, which includes at least two independently integrated switches of load for at least two independent resonant circuits. Such hardware element will have at least two pairs of outputs for connection of at least two antennas. The integration of the second switch into the PICC controller is a preferable solution; the PICC controller then does not need to have a data output.

The invention can be realized by means of existing PICC controllers, too, in such a way that the second switch, or multiple further switches, are connected to the data output of the PICC controller. The data output serves for synchronization of the switching of all switches. The data signal is generated by the control unit in PICC controller; the data signal must be lead outside from the chip onto some available output. If needed, PICC controller without data output can be used, too, whereby a demodulator is connected to the output of the PICC controller. The signal between the first antenna and the output of the PICC controller is demodulated and digital data for the control of the second switch or further switches is generated from the demodulated output. The demodulation already on the side of PICC device retrospectively reconstructs the signal from the high-frequency signal from the available NFC1 and NFC2 outputs from the PICC controller.

The advantage of the invention is mainly the significant improvement of the response amplitude (LMA - load modulation amplitude) on the side of the PCD device. This achieves a more reliable communication on larger distance already with small, miniature dimensions of the antenna on the side of the PICC device. Antenna system according to this invention communicates with common, unmodified PCD devices.

Description of drawings

The invention is further disclosed by means of drawings 1 to 10. The particular displayed ratios of dimensions of solenoid windings as well as schemas of resonant circuits are for illustration purposes only and cannot be interpreted as limiting the scope of protection.

Figure 1 depicts the change of the flat antenna of the PICC antenna for solenoid antenna with the goal of diminishing the spatial demands. On the left side a standard flat planar Lp antenna is connected to PICC controller with NFC1 and NFC2 outputs. On the right side the solenoid antenna with core is connected to the PICC controller.

Figure 2 depicts the antenna system with two solenoid windings which are placed in parallel alongside each other, where the second antenna is loaded by the independent second switch. In the lower part of the drawing, by the dashed line depicting data flow, an illustratory course of the signal is depicted, which controls both switches.

Figure 3 depicts bondings between antennas of PICC device and antenna of PCD device, whereby the second antenna on the side of the PICC device is switched by the independent switch. The bondings between antennas of PICC device and antenna of PCD devices are marked as k1 , k2. In fact, the antennas of PICC device are in close mutual vicinity; on figure 3 these are, for the purposes of clarity, depicted in different position.

Figure 4 schematically depicts the PICC controller with two switches on a single hardware element. In the left part of the drawing, by the dashed line depicting data flow, an illustratory course of signal controlling the switches is depicted.

Figure 5 is an example of the second switch with two MOS FET transistors.

Figure 6 depicts courses of voltage and signals on the antennas of PICC and PCD devices. Courses in the left part until A-A line depict the state after the connection according to this invention; the courses right to A-A line depict state without switching of the second switch, that is, according to the prior art. The first course (first in the graph from the top) depicts the course of voltage of the digital form of the data signal of the response transferred from PICC to PCD. The second course (second in the graph from the top) depicts the signal between PICC device’s outputs, marked on the figure 3 as NFC1 - NFC2. The third course (third in the graph from the top) depicts the signal between PCD device’s outputs, marked on the figure, marked on the figure 3 as ANT1 - ANT2. The fourth course (fourth in the graph from the top) depicts the detail of the cover of the signal depicted in third course (i.e. ANT1 - ANT2). This cover is subsequently detected by the inner circuits of PCD device and they reconstruct from it the exact response transferred there from the PICC device.

Figures 7 and 8 depict basic common points of the first and second antenna of PICC device. In figure 7 these are side by side; in figure 8 these are oriented perpendicularly in the shape of letter L.

Figure 9 depicts the schema of connection of the demodulator retrospectively in order to gain digital data from the analog signal between PICC controller and first antenna on the side of the PICC device. Figure 10 depicts a method of reconstruction of the signal from the high-frequency signal detected on the outputs NFC1 and NFC2 by means of demodulator. Examples of realization

Example 1

In this example according to figures 2, 3, 5 and 7 the antenna system on the side of the PICC device has two antennas 1, 2.

PICC controller 5 in this example is a standard element with at least one pair of NFC1 , NFC2 outputs, and with data digital output D. First antenna 1 is connected to NFC1 and NFC2 outputs. Within PICC controller 5, the outputs NFC1 and NFC2 are connected to the first switch 3. This is controlled by the flow of data from the control unit. The second antenna 2 is placed in parallel and just by first antenna T The second antenna 2 has an independent resonant circuit with the second switch 4, whose control is connected with the digital data output D from the PICC controller s.

In this example, both antennas 1, 2 are formed by solenoid windings which are marked as L1 and L2, too. The solenoid windings are formed by winding of the conductor on the ferrite flat core. The common build-up area of both antennas 1, 2 is significantly smaller than the surface of the standard flat NFC antenna on the side of the PICC device.

In this example the second switch 4 is external potential-free switch produced as connection of two MOS FET transistors according to figure 5.

Figure 3 depicts bondings between antennas 1, 2 of the PICC device with the antenna 6 of the PCD device during ongoing communication. Figure 6 depicts the courses of communication in a phase in which PICC device responds to the PCD device. The influence of the second antenna 2 on the detected load modulation amplitude (LMA) can be seen in the differences, whereby the first four logical bits on the figure 6 are transferred together with the synchronous support of second antenna 2 (antenna circuit L2-C2), which creates a change of the amplitude LMA2 on the antenna 6 of the PCD device, and where the second four bits on the figure 6 are transferred only by means of change in load of the first antenna 1 (antenna circuit L1-C1), which corresponds to the detected change LMA1. The connection of the second support antenna 2 does not affect the signal level on outputs NFC1 and NFC2 of the PICC controller 5 during transmission of the response. At the same time, the difference between LMA1 and LMA2 on the side of the PCD device is significant.

The resonant circuit of the second antenna 2 is not directly connected to NFC1 , NFC2 outputs of the PICC controller 5 and it takes no part in its power supply. The only task of this circuit is thus to additionally drain the energy from the magnetic field generated by the PCD device, synchronously with the modulation signal of the response, and thereby support the passive modulation of the antenna circuit of the first antenna T Since PICC controller 5 is supplied with power through resonant circuit of the second antenna 2, the load of the resonant circuit L2-C2 can be altered, modulated in much larger scope. The change of load of this resonant circuit L2-C2 is realized, for example, by voltage controlled by the second switch 4, which on the basis of response in the digital form connects/disconnects the impedance (for example, resistance) to the resonant system L2-C2. The second antenna is placed in the immediate vicinity of the first antenna 1; the load on these two resonant circuits is modulated synchronously; the overall effect on the side of the PCD circuit is totalized and thus the LMA significantly increases - through this we achieve more reliable communication at larger distance.

The induction of the first and second antenna 1, 2 in this example ranges from 750nH to 2mH and quality Q ranges from 15 to 50.

Example 2

First antenna 1 and second antenna 2 have solenoid windings with the core, whereby they are placed on a common PCB in such a way that they have mutually perpendicular L-shaped position pursuant to figure 8.

Example 3

In this example according to figure 4 the chip which fulfills a function of PICC controller 5 includes within a single hardware element the first switch 3 and second switch 4. It has thus four outputs for two antennas 1, 2. The first switch 3 and second switch 4 are connected within the chip to common data flow from the control unit CPU.

Example 4

In this example according to figure 9 a common PICC controller 5 with a single pair of outputs NFC1 , NFC2 for the first antenna 1 is used. Since this particular PICC controller 5 lacks digital data output, a demodulator 7 is connected to NFC1 and NFC2 outputs, whereby the output of the demodulator 7 is connected as control for the second switch 4.

Industrial applicability

Industrial applicability is obvious. According to this invention it is possible to industrially and repeatedly load modulate signal in antenna system on the side of the PICC device as well as produce antenna system with at least two antennas on the side of the PICC device. It is also possible, according to this invention, to produce new designs of PICC controller which includes at least two switches for separate control of the level of load of at least two independent antenna resonant circuits. List of symbols

1 - first antenna

2 - second antenna

3 - first switch

4 - second switch

5 - PICC controller

6 - antenna of the PCD device

7 - demodulator L1 , L2 - solenoid windings 1 and 2

C1 , C2 - capacities of resonant circuits 1 and 2 CPU - central processing unit NFC - near field communication

NFC 1 , NFC2 - NFC outputs from controller DATA - data signal

DEMOD - demodulation bridge

D1 , D2 - demodulation diodes

PCB - printed circuit board

AM - amplitude modulation

LMA - load modulation amplitude