WO2006073857A1

WO2006073857A1 - Method and apparatus for regulating a high voltage power supply for transposed scan display systems

Info

Publication number: WO2006073857A1
Application number: PCT/US2005/046529
Authority: WO
Inventors: Frank Melvin Koch; James Arthur Hutton
Original assignee: Thomson Licensing
Priority date: 2004-12-31
Filing date: 2005-12-20
Publication date: 2006-07-13

Abstract

In a transposed scan cathode ray tube (CRT) (i.e., vertical scan display), the modulation requirement of the fast scan current is rather large, and therefore it is proposed to separate the high voltage regulation circuitry (660) from the scan electronics of the transposed scan display. Through the use of feedback loops and short and long time constants within the regulation circuit, the high voltages of the transposed scan CRT are regulated without interfering with the scan processes of the same.

Description

METHOD AND APPARATUS FOR REGULATING A HIGH VOLTAGE POWER SUPPLY FOR TRANSPOSED SCAN DISPLAY SYSTEMS

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent application Serial No. 60/640,929 filed on December 31, 2004, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to cathode ray tubes (CRTs) for displays such as, for example, High Definition Television (HDTV). More particularly, it relates to CRTs operating in a vertical (transposed) scan mode and a method of operating the CRT in the vertical scan mode.

BACKGROUND OF THE INVENTION The popularity of HDTV has prompted an increased demand for television sets capable of displaying HDTV images. Such demand has prompted an increase in demand for larger aspect ratio, true flat screen displays having a shallower depth, increased deflection angle and improved visual resolution performance.

The demand for shallow, flat screen displays has led to efforts to improve spot performance so that spot size and shape exhibit greater uniformity across the entire screen for improved visual resolution performance. To this end, most displays now make use of dynamic focus. Increasing the deflection angle also yields an improvement in spot performance in the central area of the screen because increasing the deflection angle results in a decreased gun-to- screen distance, hereinafter referred to as the 'throw distance'. Figure 1 illustrates the basic geometrical relationship between throw distance and deflection angle for a typical CRT. Increasing the deflection angle (A) reduces the throw distance, thus allowing for production of a shorter CRT and ultimately, a slimmer television set. As the deflection angle increases, the throw distance decreases and spot size decreases in a non-linear relationship. The following formula mathematically approximates relationship between spot size and throw distance:

Spot Size « B * Throw ^M (Equation 1) where the exponent 1.4 represents an approximation taking into consideration the effects of magnification and space charge effects over a useful range of beam current. The term B represents a system-related proportionality constant. Considering this relationship, for a tube having a diagonal dimension of 760 mm, increasing the corner to corner deflection angle from 100 degrees to 120 degrees while decreasing the center throw distance, for example, from 413mm to 313mm yields a 32% reduction in spot size at the center of the screen. Increasing the deflection angle in these displays gives rise to increases in obliquity, which is defined as the effect of a beam intercepting the screen at an oblique angle, thereby causing an elongation of the spot. The problem of obliquity becomes especially apparent in CRTs having a standard horizontal gun orientation, i.e., a CRT whose guns have a horizontal alignment along the major axis of the screen. As obliquity increases, a spot having a generally circular shape at the center of the screen becomes oblong or elongated as the spot moves toward edges of the screen. Based on this geometrical relationship, in a large aspect ratio screen, such as a 16 x 9 screen, the spot appears most elongated at the edges of the major axis and at the screen comers. Thus it becomes apparent that the obliquity effect causes the spot size to grow. The following equation defines the spot size radius SS_radiai-

SS_radiai = SSn_omai/cos(A) (Equation 2) where A represents deflection angle, as measured from Dc to De as shown in Figure 1 and nominal spot size SS_nOr_mai represents the spot size without obliquity. In addition to the obliquity effect, yoke deflection effects in self-converging CRTs having a horizontal gun orientation can compromises spot shape uniformity. To achieve self convergence, CRT's typically include a horizontal yoke that generates a pincushion shaped field and a vertical yoke that generates a barrel shaped field. These yoke fields cause the spot shape to become elongated. This elongation adds to the obliquity effect by further increasing spot distortion at the three-o'clock and nine o'clock positions (referred to as the "3/9" positions) and at corner positions on the screen.

Various attempts have been made to address spot distortion and obliquity. For example, U.S. Patent No. 5, 170,102 describes a CRT with a vertical electron gun orientation whose un- deflected beams appear parallel to the short axis of the display screen. The deflection system described in this patent includes a signal generator for causing scanning of the display screen in a raster-scan fashion, thereby yielding a plurality of lines oriented along the short axis of the display screen. The deflection system also comprises a first set of coils for generating a substantially pincushion- shaped deflection field for deflecting the beams in the direction of the short axis of the display screen. A second set of coils generates a substantially barrel shaped deflection field for deflecting the beams in the direction in the long axis of the display screen. The deflection system's coils generally distort spots by elongating them vertically. This vertical elongation compensates for obliquity effects, thereby reducing spot distortion at the 3/9 and corner positions on the screen. The barrel shaped field required to achieve self convergence at 3/9 screen locations overcompensates for obliquity and vertically elongates the spot at the 3/9 and corner locations as shown in Figure 10 of the U.S. Patent No. 5, 170,102. (In effect, the barrel shaped field overcompensates, thus making the spot shape at the 3/9 position and the screen corners a vertically oriented ellipse). Orienting the electron guns along the vertical or minor axis will yield improvements in a self-converging system, but spot distortion remains problematic at the 3/9 positions and at the corner screen locations.

A need exists for a CRT system that overcomes the aforementioned disadvantages when increasing the deflection angle A and thereby reducing throw distance and thus the overall depth of the CRT. More specifically, the reduction in throw arm distance reduces the beam spread, thereby resulting in a smaller center spot.

Furthermore wide angle deflection increases the center-to-center spot growth due to increase inclination angles of the beam in the corners of the display screen. However, the shortened throw arm provided compensation, and the absolute spot size at 3/9 and the corners of the standard scan tubes (CRTs) match that of the transposed scan display device of the present principles.

SUMMARY OF THE INVENTION

Briefly, in accordance with a preferred embodiment of the present principles, there is provided a video display system that comprises a cathode ray tube having a picture display area. The display system includes a deflection system for the cathode ray tube to provide line rate scanning in a vertical direction.

A video signal processing system serves to transpose video signals supplied to the deflection system. The display system includes high voltage power supply circuit and a method for regulating the same in the transposed scan display environment.

According to one embodiment of the present principles, the high voltage regulator circuit for a transposed scan CRT includes a high voltage sensing circuit for sensing the presence of an anode voltage at the anode of the CRT, an error amplifier circuit having a one input connected to an output of the input sensing circuit, another input connected to a reference supply voltage, and an output stage having coupled to the output of the error amplifier. The output stage provides a stable anode supply voltage to a flyback transformer in the high voltage output circuit in response to the sensed presence of the anode voltage.

A short time constant feedback loop may be added around said error amplifier for increasing stability of the high voltage regulator circuit. A filtering circuit may also be provided to remove noise in the reference supply voltage provided to the error amplifier.

In accordance with a further embodiment, the high voltage sensing circuit includes an RC network connected from the input to ground and in parallel with an input resistor for increasing anode supply voltage regulation.

According to yet another embodiment, the method for regulating high voltages in a transposed scan CRT includes providing a high voltage regulator circuit having an input and an output, the high voltage regulator circuit being separate from all scan processes of the transposed scan CRT, sensing the presence of an anode voltage at the input, and regulating an anode supply voltage at the output connected to a flyback transformer in a high voltage output circuit in response to the sensed presence of the anode voltage.

In further embodiments of the present principles, at least one feedback loop is provided in the high voltage regulator circuit to increase the stability of the circuit. The feedback loop can have a short time constant. A high frequency filter may also be provided in the high voltage regulator circuit to prevent noise from affecting the anode supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference to the accompanying figures, wherein like reference numerals depict similar elements throughout the

views:

Figure 1 is a diagram depicting the basic geometrical relationship between the throw distance and deflection angle in a typical CRT;

Figure 2a is a diagrammatic cross-sectional view of a CRT according to a preferred embodiment of the present principles; Figure 2b is a diagram representing the lines and pixels of a standard scan CRT;

Figure 2c is a diagram representing the lines and pixels of the transposed scan display according to an embodiment of the present principles;

Figure 3 is a diagram of the screen of the CRT of FIG. 2 illustrating a mis-convergence pattern in accordance with the present principles; Figure 4 is a diagram depicting optimization of spot shape in accordance with the present principles;

Figure 5 is a block diagram of the transposed scan display system incorporating the high voltage regulator of the present principles;

Figures 6a-6c are illustrative schematic diagrams of the transposed scan display circuits of the present principles;

Figure 6d is an illustrative schematic diagram of the anode power supply having the high voltage regulator circuit according to an embodiment of the present principles;

Figure 7a is an illustrative schematic diagram of an oscillator circuit within the anode power supply according to an embodiment of the present principles;

Figure 7b is an illustrative schematic diagram of a high voltage regulator circuit within the anode power supply according to an embodiment of the present principles;

Figure 7c is an illustrative schematic diagram of a high voltage regulator circuit within the anode power supply according to another embodiment of the present principles;

Figure 7d is an illustrative schematic diagram of a high voltage regulator circuit within the anode power supply according to yet another embodiment of the present principles;

Figure 7e is an illustrative schematic diagram of a drive circuit within the anode power supply according to an embodiment of the present principles; and Figure 7f is an illustrative schematic diagram of the high voltage output circuit of the anode power supply according to an embodiment of the present principles;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Prior to discussing the CRT display system of the present principles, a brief discussion of the facets of a typical cathode ray tube will prove helpful. Figure 2a illustrates a cathode ray tube (CRT) 1, for example a W76 wide screen tube, having a glass envelope 2 having a rectangular faceplate panel 3 and a tubular neck 4 connected by a funnel 5. The funnel 5 has an internal conductive coating (not shown) that extends from an anode button 6 toward the faceplate panel 3 and to the neck 4. The faceplate panel 3 comprises a viewing faceplate 8 and a peripheral flange or sidewall 9, which is sealed to the funnel S by a glass frit 7. The inner surface of the faceplate panel 3 carries a three-color phosphor screen 12. The screen 12 comprises a line screen with the phosphor lines arranged in triads. Each triad includes a phosphor line of three primary colors, typically Red, Green and Blue, and extends generally parallel to the major axis of the screen 12.

A mask assembly 10 lies in a predetermined spaced relation with the screen 12. The mask assembly 10 has a multiplicity of elongated slits extending generally parallel to the major axis of the screen 12. An electron gun assembly 13, shown schematically by dashed lines in Figure 2a, is centrally mounted within the neck 4 to generate three inline electron beams, a center beam and two side or outer beams, directed along convergent paths through the mask frame assembly 10 to strike the screen 12. The electron gun assembly 13 has three vertically oriented guns, each generating an electron beam for a separate one of the three colors, Red, Green and Blue. The three guns lie in a linear array extending parallel to a minor axis of the screen 12.

The CRT 1 employs an external magnetic deflection system comprised of a yoke 14 situated in the neighborhood of the funnel-to-neck junction. When activated with deflection currents, the yoke 14 generates magnetic fields that cause the beams to scan over the screen 12 vertically and horizontally in a rectangular raster.

Conventional video signal transmission assumes a pixel-by-pixel time sequence such that transmission of Red, Green and Blue images effectively occurs as a series of scan lines proceeding from the left edge to the right edge of the image along a scan line and then moving down to the next scan line where again the signal sequence proceeds from left to right. This process continues from top to bottom, in either a progressive scan mode or an interlaced scan mode, as is known in the art. Figure 2b shows an example of a standard orientation (scan) CRT having 720 horizontally scanned lines each having a pixel width of 1280. To achieve a vertical scan (or transposed scan) display, the image must undergo a translation into a vertical scan pattern such that the signal sequence starts at the upper left hand corner of the image. The subsequent signal elements then follow along a vertical line from top to bottom along the left edge. After an appropriate retrace interval, generation of a signal element at the top edge of the image at the second scan line occurs, followed by the signal elements corresponding to a sequence from top to bottom along the second scan line. Similarly the third scan line starts at the top and proceeds to the bottom of the image, and thus the corresponding top to bottom signal element must be provided. This process continues through the last scan line at right vertical edge of the image.

To effect vertical scanning, the horizontal scan sequence must undergo a change from a conventional left-to-right and stepwise top-to-bottom regimen to a top-to- bottom and stepwise left to right transposed sequence. Figure 2c shows an example of the vertical scanning of the transposed scan display according to an embodiment of the present principles. As shown in this example, there are 1280 vertically scanned lines, each having a length of 720 pixels. For the purposes of the following discussion, the terms "Digital Orthogonal Scan" and/or DOS refer to the above-described transposition operation and is used herein interchangeably with the term "transposed scan display".

In accordance with one aspect of the present principles, the electron beam undergoes spot shaping. To understand spot shaping, a discussion of the yoke 14 and the effect of the yoke fields will prove helpful. As discussed, the yoke 14 lies in the neighborhood of the funnel-to- neck junction on the CRT 1 as shown in Figure 2a. In the illustrated embodiment, the yoke 14 has first deflection coil system (not shown) that generates a horizontal deflection yoke field that is substantially barrel-shaped. The yoke 14 has a second deflection coil system (not shown) electrically insulated from the first deflection coil system for generating a vertical yoke field that is substantially pincushion-shaped. These yoke fields affect beam convergence and spot shape. Rather than adjust for self-convergence, the horizontal barrel field shape associated with the first deflection system undergoes an adjustment (e.g., a reduction), to yield an optimized spot shape at the sides of the screen. The barrel shape of the yoke field attributable to the second deflection coil system undergoes a reduction. The combined effects of the barrel-shaped field and the dynamic astigmatism correction provided by the dynamic focus associated with the electron guns yields an optimized, nearly round spot shape at the 3/9 position and at the corner screen locations. The use of pincushion vertical field and a barrel horizontal field, where the barrel horizontal field is adjusted to improve spot shapes and allow some mis-convergence of the electron beams along the screen edges is characterized as quasi-self-convergent deflection fields.

The field reduction that results in improved spot shape from self-convergence actually causes mis-convergence at certain locations on the screen. Figure 3 illustrates a transposed scan display screen showing the resulting mis-convergence from such a reduced barrel-shaped field. 29

12

For example, when the barrel field undergoes a reduction to achieve an optimized spot at the 3/9 positions and at the corner locations of the screen, the beams over-converge at the sides of the screen. Over-convergence as used here refers to a condition that results from the red and blue beams crossing over each other prior to striking the screen. The amount of over-convergence varies as a function beam deflection. Thus, the resultant pattern appears converged at the center of the screen while appearing mis-converged at the sides of the screen. Assuming the electron gun assembly 13 of Figure 2a has its red, green, and guns orientated from top to bottom, the over-convergence causes the electron beams to generate a blue, green, red convergence pattern at the sides of the screen as seen in FIG. 3. The resultant over-convergence at the screen sides in this example was measured at 15 millimeters. Other CRT designs having different geometries or different yoke field distributions will result in more or less over-convergence, for example, in the range of 5 to 35 millimeters.

The addition of multipole coils, such as the quadrupole coils 16 shown in Figure 2a, can correct for mis-convergence, or over-convergence that results from the yoke effect described above. In particular, locating the quadrupole coils 16 on the gun side of the yoke 14 will ^' dynamically correct for the yoke effect. The quadrupole coils 16 are fixed to the yoke 14 or alternatively, can be applied to the neck and have their four poles oriented at approximately 90° angles relative to each other as is known in the art. The adjacent poles of the coils 16 have

alternating polarity and the orientation of their poles lies at 45° from the tube axes so that the

resultant magnetic field displaces the outer (red and blue) beams in a vertical direction to provide correction for the mis-convergence pattern shown in FIG. 3. Alternatively, the quadrupole coils 16 can lie behind the yoke 14 approximately at or near the dynamic astigmatism correction point of the guns of the electron gun assembly 13. Operating under dynamic control, the quadrupole coils 16 create a correction field for adjusting mis-covergence on the screen. The quadrupole coils 16 in this embodiment are driven in synchronism with the horizontal deflection. The signal driving the quadrupole coils 16 has a magnitude selected to correct the over-convergence described above. In an illustrated embodiment, the quadrupole coil signal has a waveform whose shape approximates a parabola. The electron gun assembly 13 of the CRT 1 has electrostatic dynamic focus astigmatism correction to achieve optimum focus in both the horizontal and vertical directions of each of the three beams. This electrostatic dynamic astigmatism correction occurs separately for each beam, thereby allowing for correction of the horizontal-to-vertical focus voltage differences without affecting convergence. Although the quadrupole coils 16 affect beam focus, their location near the dynamic astigmatism point of the guns of the electron gun assembly 13 allows for correction of this effect by adjusting the electrostatic dynamic astigmatism voltage so that there is a minimal effect on the spot. This enables correction of mis-convergence at selected locations on the screen without affecting the spot shape. Advantageously, modification of the yoke field design can optimize spot shape and the dynamically driven quadrupole coils 16 can correct for any resultant mis-convergence.

Figure 4 illustrates one quadrant of the screen of a W76 CRT with an aspect ratio of 16:9

and a 120° deflection angle and shows the improvement in spot shape and size obtained by the

design of the yoke 14 and the use of the quadrupole coils 16 as discussed above. The spots illustrated by the dotted lines represent the effects of throw distance and obliquity referenced to a round center spot. Optimized spots obtained in accordance with the present principles appear with solid lines. Significant improvements in spot size and shape appear at the sides and corners of the screen. Table 1 lists experimental results for an illustrative embodiment in accordance with the present principles, with H representing the horizontal dimension of each spot, and V representing the vertical dimension of each spot normalized to the center spot. Table 1 compares the cumulative effect of gun orientation, yoke field effects and dynamically controlled

quadrupole coils with dynamic astigmatism correction applied to traditional horizontal inline

gun CRTs

TABLE 1

The center column of Table 1 lists the spot dimensions for a prior art standard horizontal gun orientation CRT with self-convergent beams, whereas the right-hand column represents the results for a CRT with vertical gun alignment in accordance with the present principles wherein the beams undergo dynamically controlled convergence. Although spot shape suffers a slight compromise at the 6 O'clock and 12 O'clock screen positions (6/12 or otherwise as the top and bottom), spot size uniformity shows great improvement at the 3 O'clock and 9 O'clock positions (3/9 or otherwise as the side) and at the corner locations. The present technique advantageously provides more uniform spot shape across the screen, thus enhancing visual resolution. Although the invention is applicable to CRTs having deflection angles at 100 or above, the invention has particular applicability to much larger deflection angles such as systems exceeding 120 degrees. In general, CRT displays exhibit raster distortions. The most common raster distortions pertain to geometric errors and to convergence errors. A geometric error results from non- linearities in the scanned positions of the beams as the raster traverses the screen. Convergence errors occur in a CRT display when the Red, Green and Blue rasters do not align perfectly such that over some portion of the image, a Red sub-image appears offset with respect to the Green sub-image and the Blue sub-image appears offset to the right of the Green sub-image. Convergence errors of this type can occur in any direction and can appear anywhere in the displayed image. With known color CRT displays, both convergence and geometric errors can occur despite perfect alignment of the center region during the original manufacture of the CRT display, assuming that the deflection signals applied to the deflection -coils ramp linearly. Traditional analog circuit techniques compensate for such distortions by modifying the deflection signals from linear ramps to more complex wave shapes. Also, adjustment in the details of the yoke design can reduce convergence errors and geometry errors. As the deflection angle increases beyond 100°, however, the traditional methods of geometry and convergence corrections become more difficult to implement.

It becomes clear from the above, that when the deflection angle is increased in a transposed scan display, thereby decreasing the throw distance of the electron gun, many considerations and corrections are required in order to compensate for the negative effects on the displayed image resulting from such changes in design.

The display system of the present invention includes a video deflection system for the CRT to provide line rate scanning in a transposed or the vertical direction. This digital orthogonal scanning (DOS) provides a fast scan in the short direction of a 16:9 format screen. Figure 5 shows a block diagram of the transposed scan display system 100 according to an embodiment of the present principles. As shown, an input from a high definition (HD) video source 102, such as, for example from a cable, satellite, network or other service provider is provided to the display system. The high resolution source input is fed to an FPGA 110 where it is processed and then input into the video processor 116. In some instances, an RGB to YPrPb converter 104 may be required to input the Y, Pr and Pb signals to the video processor 116. In addition, content source 102 provides horizontal and vertical sync signals (H & V) which are processed by the FPGA 1 10 and sent to the sync processor 118. The video processor 116 outputs the RGB video signals to the video drivers 133 which drive the electron gun of the slim transposed scan (DOS) CRT 200.

The sync processor 118 outputs several signals including synchronization signals to a waveform generator 120 embodied within the microprocessor 112 in order to generate the appropriate waveform for the quad coil drivers 130, and for N-S Pincushion Modulator 124. In other contemplated embodiments, the waveform generator can be incorporated into the FPGA 110 and thus be eliminated from the microprocessor the circuit shown in Figure 3.

The sync processor 118 is responsible for handling the synchronization of the output signals to the transposed scan (DOS) CRT 200. As such, it is responsible for the fast scan (V Drive) and slow scan (H Drive) signals input to the V scan 128 and H scan 126 circuits, respectively. Sync processor 118 also provides control signals to the focus modulation generator 120, which controls the dynamic focus output 121 connected to the anode power supply 134. hi accordance with one embodiment, the video processor 116 may include OSD insertion 117 capabilities. In other contemplated embodiments, the OSD may be integrated into video processor 116, or the microprocessor 112, or the FPGA 110 without departing from the spirit of the present disclosure. Those of skill in the art will recognize that many of the components shown in the block diagram of Figure 5 can be embodied in an application specific integrated circuit (ASIC) or other specialized integrated circuit without departing from the spirit of the present principles. Examples of such circuits that could be embodied in one or more ASICS would be, FPGA 110, Microprocessor 112, RGB to YPrPb converter 104, sync processor 118, video processor 116 and/or focus modulation generator 120.

Microprocessor 112 functions to control the video processor 116, the OSD 117, the FPGA 110, and the SW mode power supply 113. An IR pickup 114/ keyboard or other user interface device may be connected to the microprocessor for providing remote control capability to the system 100.

The Anode power supply outputs the heater voltage and G2, G3 and G5 voltages to the . appropriate pins (not shown) of the electron gun 13. In addition, it provides a 3OkV anode voltage to the transposed scan CRT 200. The quad drivers 130 drive the quad coils 16 of the CRT, and the V scan 128 and H scan 126 circuits drive the yoke 14. The video drivers 133 provide the video signals to the electron gun for display on the CRT 200. The fast scan sync waveform generated by the V scan circuit 128, is used by: the sync processor 1 18 for phase correction; the video processor 116 to generate blanking; the SW mode power supply 113 for synchronization and the anode power supply 134 for synchronization. The present principles provide a method and corresponding circuitry for implementing a high voltage regulator for transposed scan CRTs. As mentioned above, the reducing of the depth of a CRT requires the increasing of the deflection angle. The reduction of the deflection inherently results in much greater geometric distortions that require electronic correction. As such, high voltage regulation is integral to maintaining near perfect raster size and geometric stability, regardless of the varying loading of the anode power supply with normal anode current variations. The high voltage regulator according to the present principles separates the high voltage regulation from the scan processes and circuits. Since the modulation requirements on the fast scan of the transposed scan CRT are very high, it is preferred to separate the high voltage regulation from the scan process. This serves to increase the stability of the high voltages used to drive the transposed scan CRT with increased deflection angles.

Figures 6a-6d show exemplary schematic circuit diagrams blocked according to the block diagram of Figure 5. The details of the inter- workings of these circuits are described below with reference to the schematic diagrams shown in Figures 7-9.

Figure 6d shows the anode power supply 134 and high voltage regulator 660. According to one aspect of the present principles, anode power supply 134 includes several circuits 650, 660, 670 and 680, which are now described with reference to Figures 7a-7d.

Figure 7a shows an exemplary circuit diagram of an oscillator circuit 650 according to an embodiment of the present principles. This oscillator circuit 650 functions to maintain the phase control of the anode power supply by adjusting the timing of the high voltage drive so as to ^■ properly phase the scan with respect to the video. The oscillator 650 also functions to: 1) provides a reference +5 volt supply at output 710A to the regulator circuit 660 at input 710B (Figure 7b); and 2) receives an input signal 720A from output 720D of the high voltage circuit 680 (Figure 7d) to sense phase and prevent failures of the circuit, and more particularly to prevent failure in the operating transistor LQ610 in the high voltage circuit 680.

Figure 7b shows an exemplary circuit diagram of the high voltage regulator circuit 660A according to an embodiment of the present principles. As mentioned above, in the transposed scan display system of the present principles, the modulation requirements on the fast scan current is extremely high, and as such, it is preferred to separate the high voltage regulation from the scan process. As such, circuit 660A has been implemented to regulate the high voltage of the transposed scan display.

The regulator circuit 660A outputs a high voltage supply voltage HVB+ at output 730B to the input 730D of the high voltage circuit 680 (Figure 7e). Circuit 660A includes two portions 662 and 664 that operate to regulate the high voltage supply to the transposed scan display. Circuit portion 664 is a feedback of the regulator output to the amplifier LU602 and functions to stabilize the amp LU602 and thereby the entire circuit 660. In order to sense the Anode voltage, a high voltage resistor (not shown) is tied from the anode to the input of block 662, "HIGH_VOLTAGE_DIVIDER_INPUT". This works in conjunction with the resistor network LR635, LR634, and LR613 to provide -2.5 volts to the FET input op-amp LU602 when there is 30 kV on the anode. Resistor LR632 and capacitor LC610 provide high frequency filtering to prevent video or other noise sources from affecting the anode supply voltage. The op-amp LU602 is in a voltage follower configuration to provide a low impedance drive to the next stage.

The basic error amplifier of the high regulator circuit 660A consists of op amp LU602 (outside block 662), transistor LQ610, transistor LQ607 and associated resistors. The two inputs to op-amp LU602 are a +5 V reference 710B, and the output of high voltage sensing stage 662. The +5 V reference is filtered to remove noise by resistor LR625 and capacitor LC611. Since the composite amplifier has a phase inversion created by transistor LQ610 the + input of the op-amp LQ602 is the - input of the total amplifier. So the gain of the amplifier is set by the feedback network 664 where resistor LR630 is the Rf and LR624 is the Ri in the equation Gain - RfTRi, (i.e., 100k / 2.2k = 45.45). Since the open loop gain is 153 to 91-6, the closed loop gain set by the feedback resistors in network 664 is ~ 45.

According to one preferred embodiment, transistor LQ610 has a gain of- LR629 / LR628 = 8.33, and transistor LQ607 operates as a gate follower with a gain of- 1. In accordance with one embodiment shown in Figure 7c, the feedback resistor LR608 could be replaced with a capacitor LC608 (e.g., having a value of ~100pF). However, the use of a feedback resistor LR608 (e.g., 2.2 megohm) shown in the embodiment of Figure 7b, has proven to increase circuit stability. The use of this feedback resistor LR608 reduces the op-amp gain to the equivalent of about LC608 / LR626, 2.2M / 20k = 110 for most frequencies and about LC608 / (LR626 + LR625) = 18.33 for frequencies significantly less than 16 Hz.

Figure 7d shows the high voltage regulator circuit 660c according to another embodiment of the present principles. In this embodiment, resistor RL630 has been removed from feedback block 664 and an added RC network connected from the input to ground in parallel with LR635. This greatly improves the anode voltage regulation. It has been found that the feedback of block 664 is not required and therefore has been eliminated from this embodiment. Those of skill in the art will recognize that high voltage sensing circuit 662 operates at 5.0 volts instead of 2.5 volts in this embodiment.

In all of the embodiments of circuits 660 shown, the high voltage B+ (HVB+) 730B normally operates near 120 V. This is the high voltage B+ 730D in circuit 680 (see Figure 7f) that supplies the flyback LT601 and its parallel energy storage inductor LT602. The flyback pulse has a peak voltage of nearly 1000 V to generate 30 kV at the anode with no or light loads. So the overall gain from output 730B to the anode is ~ 30 kV / 120 V = 250.

In the various embodiments, there are feedback loops that are used to maintain stability in the high voltage regulator circuit 660. These loops are: 1) Capacitor LC608 around the op- amp LU602 (Figure 7b) or Resistor LR608 around op amp LU602 (Figures 7b and 7c); 2) block 664 around the composite amplifier (Figures 7b and 7c); and, 3) the high voltage resistor from the anode (e.g., 300 Megohm, not shown). Feedback loops 1 and 2 are short time -constant loops, while feedback loop 3 is a long time constant loop. Feedback from the anode is not very fast since there are capacitors on the anode and the output impedance of the flyback is not low, so these additional loops were added to prevent oscillations.

Figure 7e shows an exemplary circuit diagram of the drive circuit 670 within the anode power supply according to an embodiment of the present principles. Drive circuit 670 provides the drive voltage and waveform to the drive transformer (e.g, LT600) in the high voltage circuit 680. The drive circuit 670 receives the high voltage drive signal (HVDRV) at from the oscillator circuit 650. The HVDRV signal is applied at input 750D for the drive circuit 670. The driver circuit outputs the HVDRV+ signal at output 740C, where it is input to the high voltage circuit at input 740D (Figure 7f).

Figure 7f shows an exemplary circuit diagram of a high voltage output circuit 680 within the anode power supply according to an embodiment of the present principles. The input at 730D is the HVB+ output from the high voltage regulator circuit 660 and is used to supply the flyback transformer LT601 and its parallel energy storage inductor LT602. By sensing changes in the anode voltage, the HVB+ can be adjusted to maintain the anode voltage constant with changes in the load due to changing video content. Those of skill in the art will recognize that the changing video content can have a direct effect on the anode voltage. As such, regulating the anode voltage minimizes visual changes in raster size and/or ringing.

While there have been shown, described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions, substitutions and changes in the form and details of the methods described and devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed, described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

1. A high voltage regulator circuit for a transposed scan CRT, the circuit comprising: a high voltage sensing circuit (660) for sensing the presence of an anode voltage at the anode of the CRT; an error amplifier circuit having a one input connected to an output of the input sensing circuit, another input connected to a reference supply voltage, and an output; an output stage having coupled to said output of said error amplifier, said output stage providing a stable anode supply voltage to a flyback transformer in a high voltage output circuit in response to the sensed presence of the anode voltage.

2. The high voltage regulator circuit according to claim 1, further comprising: a short time constant feedback loop disposed around said error amplifier for increasing stability of the high voltage regulator circuit.

3. The high voltage regulator circuit according to claim 1, further comprising a filtering circuit to remove noise in the reference supply voltage provided to said error amplifier.

4. The high voltage regulator circuit according to claim 1, wherein said high voltage sensing circuit includes an RC network (RC) connected from the input to ground and in parallel with an input resistor for increasing anode supply voltage regulation.

5. A method for regulating high voltages in a transposed scan CRT comprising: providing a high voltage regulator circuit (660) having an input and an output, said high voltage regulator circuit being separate from all scan processes of the transposed scan CRT; sensing the presence of an anode voltage at the input; and regulating an anode supply voltage at the output connected to a flyback transformer in a high voltage output circuit in response to the sensed presence of the anode voltage.

6. The method according to claim 5, further comprising: providing at least one feedback loop in the high voltage regulator circuit to increase the stability of said circuit; and providing high frequency filtering in the high voltage regulator circuit to prevent noise from affecting the anode supply voltage.

7. The method according to claim 6 wherein said providing at least one feedback loop further comprises providing a feedback loop having a short time constant.