METHOD FOR ADJUSTING VIDEO DISPLAY APPARATUS

CROSS REFERENCE TO RELATED APPLICATIONS This application is related to concurrently filed applications entitled "Method for adjusting convergence in a television receiver" with Attorney's docket number PU050150 and "Deflection apparatus having raster positioning circuitry" with Attorney's docket number PU050085, all by the same inventor.

FIELD OF THE INVENTION The present invention generally relates to video display apparatuses such as television signal receivers and/or monitors, and more particularly, to a method for adjusting a video display apparatus using main deflection coils to control raster positioning.

BACKGROUND OF THE INVENTION

Video display apparatuses such as television signal receivers or monitors often include circuitry that allows for the correction of the raster on the face of a cathode ray tube (CRT). In particular, such corrections are useful for correcting picture offsets that result from local magnetic field changes. For example, when an apparatus such as a television signal receiver is physically moved, the magnetic field around the tubes may change and thereby cause the picture to rotate or become off-centered.

To correct this condition, the aforementioned corrections including a centering function may be performed to restore the picture to its proper alignment. The centering function may for example be accomplished by causing a direct current (DC) of selected polarity and magnitude to flow through coils of the CRTs. The need for this centering function may increase as overscan of a tube is reduced, that is, as the raster width approaches the width of the tube face.

Conventional video display apparatuses, such as rear projection televisions using CRTs, typically use the convergence coils of the CRTs (as opposed to the main deflection coils) for raster positioning when performing

the aforementioned corrections. This approach is relatively simple from a control and complexity standpoint, but may be stressful on the convergence related electronic components of the video display apparatus and therefore require expensive mitigation techniques, such as large heat sinks, to prevent ultimate damage to such components over time. Performing such corrections using the main deflection coils of the CRTs for raster positioning has historically been expensive and somewhat unstable, but is desirable since the main deflection coils may require less DC current to cause the same picture centering effect.

The present invention described herein provides methods for performing the aforementioned corrections to a video display apparatus, including a method that uses the main deflection coils of the CRTs to control raster positioning.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a method for adjusting a video display apparatus is disclosed. According to an exemplary embodiment, the method comprises performing a first deflection correction using main deflection means of the video display apparatus and performing a second deflection correction using convergence means of the video display apparatus.

In accordance with another aspect of the present invention, a video display apparatus is disclosed. According to an exemplary embodiment, the video display apparatus comprises main deflection means for performing a first deflection correction of the video display apparatus and convergence means for performing a second deflection correction of the video display apparatus.

In accordance with another aspect of the present invention, a television signal receiver is disclosed. According to an exemplary embodiment, the television signal receiver comprises main deflection coils operative to perform a first deflection correction of the television signal receiver and convergence

coils operative to perform a second deflection correction of the television signal receiver.

In accordance with yet another aspect of the present invention, a method for adjusting a projection television display apparatus is disclosed. According to an exemplary embodiment, the method comprises performing center convergence using a main deflection means of the projection television display apparatus and performing dynamic convergence using a convergence means of the projection television display apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a front view of a video display apparatus according to an exemplary embodiment of the present invention;

FlG. 2 is another diagram of a video display apparatus according to an exemplary embodiment of the present invention;

FIG. 3 is a circuit diagram of the horizontal centering circuit and photo coupler of FIG. 2 according to an exemplary embodiment of the present invention;

FIG. 4 is a flowchart illustrating steps for adjusting a video display apparatus according to an exemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating a sensor search technique according to an exemplary embodiment of the present invention; and

FIG. 6 is a flowchart illustrating steps for adjusting a video display apparatus according to another exemplary embodiment of the present invention.

The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1, a front view of a video display apparatus according to an exemplary embodiment of the present invention is shown. Video display apparatus of FIG. 1 comprises a plurality of cathode ray tubes with raster scanned images which are projected onto screen 700. Cabinet C supports and surrounds screen 700 and provides visible picture display area VA 800 which is slightly smaller than screen 700. In FIG. 1, screen 700 is depicted with a broken line to indicate an edge area which is concealed within cabinet C, and which may be illuminated with raster scanned images when operated in an over scan mode as indicated by area OS. Photo transistor sensors S1 to S8 are located adjacent to the periphery of screen 700 within the concealed edge area and outside visible picture display area VA 800. As indicated in FIG. 1 , photo transistor sensors S1 to S8 are positioned at the corners and at the centers of the edges of screen 700. With these sensor positions, it is possible to detect and measure an image formed by an electronically generated test pattern, for example, a non-peak video value block M. By sensing the illumination of sensors S1 to S8 by block M, determinations regarding picture width and height and certain geometric errors (e.g., rotation, bow, trapezium, pincushion etc.) may be made, and corrections may be performed to provide a properly aligned picture.

Referring now to FIG. 2, another diagram of a video display apparatus according to an exemplary embodiment of the present invention is shown. The general operation of the video display apparatus of FIG. 2 will now be described. In FIG. 2, three CRTs, R, G and B form raster scanned monochromatic color images which are directed through individual lens systems to converge and form a single display image on screen 700. Each CRT is depicted with four coils which provide horizontal and vertical deflection and horizontal and vertical convergence. The horizontal deflection coils of the CRTs are driven by horizontal deflection circuit 600. A horizontal centering operation of the horizontal deflection coils is controlled via horizontal centering circuit 625 and photo coupler 675, which will be described later herein. The vertical deflection coils of the CRTs are driven by vertical deflection amplifier

650. The horizontal and vertical deflection coils represent the main deflection means of the video display apparatus, and are generally larger in inductance than the horizontal and vertical convergence coils.

In FIG. 2, horizontal deflection circuit 600 and vertical deflection amplifier 650 are driven with deflection waveform signals that are controlled in amplitude and wave shape via a data bus 951 and synchronized with the signal source (SS) selected for display. Exemplary green channel horizontal and vertical convergence coils 615 and 665 respectively, are driven by amplifiers 610 and 660 respectively, which are supplied with convergence correction waveform signals. The correction waveform signals GHC and GVC may be considered representative of DC and AC convergence signals, for example static and dynamic convergence, respectively. These functional attributes may be facilitated as follows. An apparent static convergence or centering effect, for example, can be achieved by modifying all measurement location addresses by the same value or offset to move the complete raster. Similarly, a dynamic convergence effect may be produced by modification of the location address of a specific measurement location. Correction waveform signals GHC and GVC for the green channel are generated by exemplary digital-to-analog converters (DACs) 311 and 312 which convert digital values read from memory 305 into horizontal and vertical deflection currents, respectively. Similarly, red and blue correction waveform signals are generated by digital-to-analog conversion of digital values read from memory 305.

Also in FIG. 2, an input display video selector selects, by means of bus 951, between two signal sources IP1 and IP2, for example, a broadcast video signal and an SVGA computer generated display signal. Video display signals RGB, are derived from the display video selector and electronically generated message information, for example, user control information, display setup and alignment signals and messages generated responsive to commands from controllers 301 , 900 and 950, are coupled via buses 302 and 951, and may be combined by on screen display generator 500.

During an automated correction process of the video display apparatus, controller 900 sends commands via data bus 302 to controller 301 which instructs video generator 310 to generate test signals such as an exemplary green channel calibration video test signal AV comprising an exemplary black level signal with rectangular block M (also see FIG. 1) having a predetermined video amplitude value. Controllers 900 and 301 also control the generation of block M to illuminate sensors S1 to S8 by determining horizontal and vertical timing to position block M within the scanned display raster. Alternatively, controllers 900 and 301 can move the scanned raster, or a part of the scanned raster containing block M to achieve sensor lighting. Advantageously, both methods may be employed to facilitate precision movement of block M relative to sensors S1 to S8. An exemplary green channel test signal AV may be output from IC 300 and combined at amplifier 510 with the green channel output signal from on screen display generator 500. The output signal from amplifier 510 is coupled to exemplary green CRT, and may include display source video, and/or other type of display content. Controller 301 also executes a program stored in programmable read-only memory (PROM) 550 which comprises various algorithms.

Also during the automated correction process of the video display apparatus, controller 301 outputs a digital word D (e.g., 8 bits) on data bus 303, which is coupled to controllable current source 250. The digital word D represents a specific current to be generated by current source 250 and supplied to sensors S1 to S8 and sensor detector 275. To facilitate correction and alignment of three color images during the automated correction mode, block M is generated as described previously and coupled to the CRTs. In FIG. 1, for example, block M is shown approaching sensor S1. As previously indicated, each sensor S1 to S8 may be illuminated by block M having a precisely generated timing within a video signal projected with an overscanned raster. Alternatively, block M may cause illumination by positioning, or shifting the. scanned raster such that block M lights a given sensor S1 to S8, or with a combination of both. With certain display signal inputs, for example computer display format signals, substantially all of the scanned area can be utilized for signal display, thus the raster is not

overscanned. During operation with computer display format signals, raster overscan is limited to a nominal few percent, for example 1%. Hence, under these substantially zero overscan conditions, sensors S1 to S8 may be illuminated by raster positioning of block M. Individual sensor illumination may be facilitated with a combination of both video signal timing and raster positioning.

In each sensor S1 to S8, photon-generated carriers enable transistor conduction of current 11 to I8, respectively, in a substantially linear relationship to the intensity of the illumination incident thereon. However, the intensity of illumination at each individual sensor S1 to S8 may vary greatly for a number of reasons, for example, the phosphor brightness of each individual CRT may be different, and there may be lens and optical path differences between the three monochromatic color images. As each CRT ages, the phosphor brightness may decline. Furthermore with the passage of time, dust may accumulate within the optical projection path to reduce the intensity of illumination at sensors S1 to S8. A further source of sensor current 11 to I8 variability results from variations in sensitivity between individual sensors S1 to S8 and their inherent spectral sensitivity. For example, in a silicon sensor, sensitivity is low for blue light and increases through the green and red spectrum to reach a maximum in the near infra red region. Accordingly, it may be appreciated that each individual sensor S1 to S8 may conduct widely differing photo-generated currents. Hence, to facilitate stable, repeatable measurements, it is important that these sensor current variations are individually measured and a detection threshold set for each sensor S1 to S8 and illuminating color. This is done at the beginning of each correction process using lighted block M which is sized and positioned to sequentially light each sensor S1 to S8. Using a fixed reference current Iref, the detection level is switched to a different level for each color, and the brightness of block M is stepwise increased until each sensor S1 to S8 sees light, as indicated by current lsen exceeding reference current Iref. A slightly higher brightness level is stored in memory 305 and used for subsequent testing at a given sensor S1 to S8 in the immediate correction process. If light is not seen at a

given sensor S1 to S8, the correction process is stopped and an error message is displayed.

The widely differing photo-generated sensor currents 11 to I8 described above may be advantageously compensated, calibrated and measured by means of control loop 100 depicted in FIG. 2. Sensor detector 275 is depicted in circuit block 200 of FIG. 2. In simple terms, reference current lref is generated by current source 250 and supplied to a given sensor S1 to S8 and sensor detector 275. In the absence of illumination, the given sensor S1 to S8 represents a high impedance and consequently diverts an insignificant current, Isen, from reference current lref. Thus, a majority of reference current lref is coupled to sensor detector 275 as current Isw. Current Isw biases sensor detector 275 such that the output state is low, which is chosen to represent an unlit or un-illuminated state.

When a given sensor S1 to S8 is illuminated, a photo-generated charge causes the given sensor S1 to S8 to turn on and conduct current Isen from reference current lref. Since reference current lref is generated by a constant current source 250, current Isen is diverted from sensor detector 275 current Isw. At a particular illumination level, the given sensor S1 to S8 diverts sufficient current from sensor detector 275 to cause it to switch off and assume a high, nominally supply voltage potential, which is chosen to be indicative of a lit or illuminated state. The output from sensor detector 275 is positive-going pulse signal 202 which is coupled to an input of digital convergence IC STV2050. The rising edge of pulse signal 202 is sampled which causes horizontal and vertical counters to stop thus providing counts which determine where in the measurement matrix the lit sensor S1 to S8 occurred.

Referring now to FIG. 3, a circuit diagram of horizontal centering circuit

625 and photo coupler 675 of FIG. 2 according to an exemplary embodiment of the present invention is shown. In FIG. 3, photo coupler 675 is labeled accordingly, and the remaining elements are part of horizontal centering

circuit 625. Accordingly, horizontal centering circuit 625 comprises Darlington switches 10 and 20, power rectifier 30, and various other circuit elements.

Darlington switch 10 comprises transistors Q11 and Q12, resistor R11, and diode D11. Darlington switch 20 comprises transistors Q21 and Q22, resistor R22, and diode D21. Power rectifier 30 comprises diodes D31 to

D34, zener diode D35, and capacitor C31. Other circuit elements of horizontal centering circuit 625 include resistors R1 to R4, diodes D1 and D2, capacitors C40 and C41, and inductor L_SHUNT. Preferred values for the foregoing circuit elements are shown in FIG. 3.

As indicated in FIG. 3, Darlington switches 10 and 20 are coupled in inverse series and thereby control the current through inductor LJSHUNT and the horizontal deflection coils of the CRTs (see FIG. 2). Darlington switch 10 includes transistors Q11 and Q12 which conduct a first current having a first polarity. Diode D21 of Darlington switch 20 acts as a rectifier coupled in series with transistors Q11 and Q12 of Darlington switch 10 and also conducts this first current. Similarly, Darlington switch 20 includes transistor Q21 and Q22 which conduct a second current having a second polarity opposite to the first polarity. Diode D11 of Darlington switch 10 acts as a rectifier coupled in series with transistors Q21 and Q22 of Darlington switch 20 and also conducts this second current. Power rectifier 30 is operative to provide 5 volts DC power to photo coupler 675. Capacitors C40 and C41 perform a dual function of limiting voltage across Darlington switches 10 and 20, and limiting current to power rectifier 30.

According to principles of the present invention, it is the ratio of the magnitude of the first current conducted by Darlington switch 10 to the magnitude of the second current conducted by Darlington switch 20 that controls the horizontal centering function of the video display apparatus of FIG. 2. According to an exemplary embodiment, a control signal from control logic 301 (see FIG. 2) causes photo coupler 625 to generate a turn off pulse for Darlington switches 10 and 20 that can be timed to block the first current, the second current, or a proportional combination of the first and second

currents provided to inductor L-SHUNT. The net current present in inductor L_SHUNT has a DC component that also flows to the horizontal deflection coils of the CRTs. This DC current controls the horizontal centering function performed by the CRTs of FIG. 2, and may exhibit various amplitudes positive or negative, or zero when the first and second currents respectively provided by Darlington switches 10 and 20 are equal. According to principles of the present invention, the use of horizontal centering circuit 625 and photo coupler 675 described above allows the main deflection coils of the CRTs to be used for picture centering corrections to the video display apparatus.

Referring to FIG. 4, a flowchart illustrating steps for adjusting a video display apparatus according to an exemplary embodiment of the present invention is shown. For purposes of example and explanation, the steps of FIG. 4 will be described with reference to the video display apparatus of FIGS. 1 and 2. The steps of FIG. 4 are merely exemplary, and are not intended to limit the present invention in any manner.

At step 41 , the correction process for the video display apparatus starts. At step 42, the original factory settings for the CRTs are restored and the factory reference positions of sensors S1 to S8 are recalled from memory 305. At step 43, the optical on-axis CRT is selected. According to an exemplary embodiment, the on-axis CRT selected at step 43 is the green CRT, as indicated in FIG. 2.

At step 44, a vertical edge find is performed using the horizontal deflection coil of the on-axis (e.g., green) CRT to move block M. According to an exemplary embodiment, the vertical edge find is performed at step 44 at sensor S2 located at the top center of screen 700 (see FIG. 1). Also according to an exemplary embodiment, the vertical edge find is performed at step 44 using a sensor search technique represented in FIG. 5. In particular, FIG. 5 illustrates a sensor search technique that may be used for each of the eight sensors S1 to S8 shown in FIG. 1. The blocks shown in FIG. 5 represent lighted areas of block M, the relative sizes of block M, and the sequence and direction of motion of block M when performing a search for

each of the eight sensors S1 to S8 shown in FIG. 1. Accordingly, the vertical edge find at sensor S2 of FlG. 1 may be performed at step 44 through two individual movements of block M represented by blocks 6 and 7 in FIG. 5.

At step 45, the horizontal deflection coil for the on-axis (e.g., green)

CRT is set to minimize the distance from sensor S2 to the centered vertical high contrast video edge of block M. The setting for the horizontal deflection coil for the on-axis (e.g., green) CRT is also applied to the horizontal deflection coils for the other (e.g., red and blue) CRTs at step 45, and all horizontal deflection settings are stored in memory 305.

At step 46, a horizontal edge find is performed using the vertical deflection coil of the on-axis (e.g., green) CRT to move block M. According to an exemplary embodiment, the horizontal edge find is performed at step 46 at sensor S4 located at the right center of screen 700 (see FIG. 1). Also according to an exemplary embodiment, the horizontal edge find is performed at step 46 using the sensor search technique represented in FIG. 5. Accordingly, the horizontal edge find at sensor S4 of FlG. 1 may be performed at step 46 through two individual movements of block M represented by blocks 15 and 16 in FIG. 5.

At step 47, the vertical deflection coil for the on-axis (e.g., green) CRT is set to minimize the distance from sensor S4 to the centered horizontal high contrast video edge of block M. The setting for the vertical deflection coil for the on-axis (e.g., green) CRT is also applied to the vertical deflection coils for the other (e.g., red and blue) CRTs at step 47, and all vertical deflection settings are stored in memory 305.

At step 48, a three-color convergence process is performed using the horizontal and vertical convergence coils of the three CRTs. According to an exemplary embodiment, the three-color convergence process is performed at step 48 using the sensor search technique represented in FIG. 5. In particular, a search for each of the eight sensors S1 to S8 is performed for each of the three colors (i.e., red, green, blue) using the convergence coils of

their respective CRTs to move block M. In this manner, each of the eight sensors S1 to S8 can be searched for a given color through thirty-six individual movements of block M. When performing the three-color convergence process at step 48, the respective convergence coils are used to distort each color according to the difference between the current detected positions of sensors S1 to S8 and their factory reference positions.

At step 49, the convergence settings yielded from the three-color convergence process of step 48 are stored in memory 305, and the normal video mode of the video display apparatus is restored. It is noted that the steps of FIG. 4 may be automatically performed in response to a predetermined input to the video display apparatus.

Referring to FIG.6, a flowchart illustrating steps for adjusting a video display apparatus according to another exemplary embodiment of the present invention is shown. For purposes of example and explanation, the steps of FlG. 6 will be described with reference to the video display apparatus of FIGS. 1 and 2. The steps of FIG. 6 are merely exemplary, and are not intended to limit the present invention in any manner.

Steps 61 to 63 of FIG. 6 are substantially identical to steps 41 to 43 of FIG. 4, and therefore will not be described again. At step 64, a vertical edge find is performed using the horizontal convergence coil of the on-axis (e.g., green) CRT to move block M. According to an exemplary embodiment, the vertical edge find is performed at step 64 at sensor S2 located at the top center of screen 700 (see FIG. 1 ) using the sensor search technique represented in FIG. 5. Accordingly, the vertical edge find at sensor S2 of FIG. 1 may be performed at step 64 through two individual movements of block M represented by blocks 6 and 7 in FlG. 5.

At step 65, the horizontal convergence coil for the on-axis (e.g., green) CRT is used to minimize the distance from sensor S2 to the centered vertical high contrast video edge of block M. Then at step 65, a look-up table stored in memory 305 is used to transfer this centering correction setting for the

horizontal convergence coil for the on-axis CRT to all of the horizontal deflection coils. These horizontal deflection settings are stored in memory 305.

At step 66, a horizontal edge find is performed using the vertical convergence coil of the on-axis (e.g., green) CRT to move block M. According to an exemplary embodiment, the horizontal edge find is performed at step 66 at sensor S4 located at the right center of screen 700 (see FlG. 1) using the sensor search technique represented in FIG. 5. Accordingly, the horizontal edge find at sensor S4 of FIG. 1 may be performed at step 66 through two individual movements of block M represented by blocks 15 and 16 in FIG. 5.

At step 67, the vertical convergence coil for the on-axis (e.g., green) CRT is used to minimize the distance from sensor S4 to the centered horizontal high contrast video edge of block M. Then at step 67, the look-up table stored in memory 305 is used to transfer this centering correction setting for the vertical convergence coil for the on-axis CRT to all of the vertical deflection coils. These vertical deflection settings are stored in memory 305. Steps 68 and 69 of FIG. 6 are substantially identical to steps 48 and 49 of

FIG. 4, and therefore will not be described again. It is noted that the steps of

FIG. 6 may be automatically performed in response to a predetermined input to the video display apparatus.

As described herein, the present invention provides methods for adjusting a video display apparatus, including a method that uses the main deflection coils of the CRTs to control raster positioning. While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.