JP2007243443A - Television receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a television receiver having no image strain even if there is a change in high voltage. <P>SOLUTION: The television receiver comprises a CRT for displaying an image, a vertical deflection circuit for generating a vertical drive signal for vertically deflect an electron beam irradiated on the screen of the CRT, a horizontal deflection circuit for generating a horizontal drive signal for horizontally deflecting the electron beam irradiated on the CRT screen, and a horizontal amplitude correction circuit for correcting the amplitude of the horizontal drive signal based on the vertical drive signal. By correcting the amplitude of the horizontal drive signal by the horizontal amplitude correction circuit, image strain generated at both ends of the CRT screen can be corrected. The horizontal amplitude correction circuit 8 is equipped with a clip circuit 20 for limiting the amplitude of the vertical drive signal to a prescribed value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a television receiver using a CRT (Cathode Ray Tube), and more particularly to an improvement of a correction circuit for correcting image distortion which is a problem in a large CRT.

  In a television receiver using a CRT as a display, it is well known that barrel-shaped image distortion 51 occurs at both ends of a CRT screen 50 as shown in FIG. Such image distortion 51 occurs because the spherical radius of the phosphor screen of the CRT is larger than the radius from the deflection center (electron gun) of the electron beam to the phosphor screen, and thus the distance between the electron gun and the phosphor screen. This is because the length becomes longer from the center of the phosphor screen toward the outside, and the path of the electron beam irradiated to the vicinity of the center of the phosphor screen is shortened and the deflection width is reduced. When the image distortion 51 occurs, the screen becomes unsightly because the raster width is insufficient. Such image distortion 51 is particularly noticeable when a large (for example, 24 inches or more) CRT is used.

  As described above, the image distortion 51 occurs due to insufficient beam deflection near the center of the screen. To correct this, the horizontal drive current generated by the horizontal deflection circuit is changed near the center of the screen. It is only necessary to stretch at. Therefore, it has been conventionally performed to eliminate image distortion by adding a correction circuit to the horizontal deflection circuit and correcting the amplitude of the horizontal drive signal. Such horizontal drive signal correction is described in, for example, Patent Document 1 and Patent Document 2 described later.

  By the way, when the image displayed on the CRT screen is switched from a dark image to a bright image, the beam current suddenly increases in the tube to cause a high voltage fluctuation, which causes all the voltages in the CRT to fluctuate. As a result, the vertical drive signal is also affected, and when the beam current increases, the amplitude of the vertical drive signal increases. Therefore, when the horizontal drive signal is corrected based on the vertical drive signal, the amplitude of the vertical drive signal is increased, so that the horizontal drive signal is corrected more than necessary.

  In the manufacturing stage of a television receiver, the amplitude of the correction signal for correcting the horizontal drive signal is adjusted to a predetermined reference value by a semi-fixed resistor provided in the correction circuit. In use, when the amplitude of the vertical drive signal increases due to the change in luminance of the video as described above, the amplitude of the correction signal becomes larger than the reference value. For this reason, there is a problem that the correction is excessively effective by the correction signal of a large level, and this causes image distortion at the edge of the screen. Patent Document 1 and Patent Document 2 do not disclose countermeasures for such problems.

  In Patent Document 3 described later, a vertical linearity correction circuit having two diodes connected in parallel in opposite directions is provided, and the impedance of the vertical deflection circuit is reduced in the vicinity of the center of the screen, so that the center of the screen It is disclosed to reduce the white band-like portion appearing in the part. However, this correction circuit is for correcting the impedance of the vertical deflection circuit, and does not correct the amplitude of the horizontal drive signal as described above. The two diodes provided in the correction circuit also have a combined impedance. The function is essentially different from that of the clipping diode of the present invention described later. Therefore, patent document 3 cannot become a clue which solves the problem mentioned above.

JP-A-7-95438 JP 2004-350180 A JP-A-11-308626

  As described above, in a conventional television receiver equipped with a correction circuit for correcting barrel-shaped image distortion, the vertical drive signal fluctuates due to high-voltage fluctuations due to changes in the image. The correction of the horizontal drive signal by the circuit is too effective, and there is a problem that image distortion occurs.

  Accordingly, an object of the present invention is to provide a television receiver in which image distortion does not occur even when there is high-pressure fluctuation.

  The present invention relates to a CRT that displays an image, a vertical deflection circuit that generates a vertical drive signal for vertically deflecting an electron beam applied to the screen of the CRT, and a horizontal deflection of the electron beam applied to the screen of the CRT. A horizontal deflection circuit for generating a horizontal drive signal for correcting the horizontal drive signal, and a horizontal amplitude correction circuit for correcting the amplitude of the horizontal drive signal based on the vertical drive signal, wherein the horizontal amplitude correction circuit corrects the amplitude of the horizontal drive signal. Thus, in the television receiver in which image distortion occurring at both ends of the CRT screen is corrected, a clip circuit for limiting the amplitude of the vertical drive signal to a constant value is provided in the horizontal amplitude correction circuit.

  In the present invention, when the image on the screen is switched from a dark image to a bright image, even if a high voltage fluctuation occurs due to an increase in the beam current and the amplitude of the vertical drive signal increases, the amplitude is limited by the clip circuit. The level of the vertical drive signal is suppressed to a constant value. For this reason, it can be avoided that the amplitude correction of the horizontal drive signal is too effective and image distortion occurs.

  In a preferred embodiment of the present invention, a variable resistor for adjusting the level of the horizontal correction signal for correcting the amplitude of the horizontal drive signal is provided, and this variable resistor is applied to a constant level vertical drive signal clipped by the clipping circuit. On the other hand, adjustment is made so that image distortion does not occur. As a result, even if the amplitude of the vertical drive signal varies due to a change in luminance of the video, the amplitude of the horizontal correction signal is always maintained at a constant value adjusted by the variable resistor, and image distortion does not occur.

  In a preferred embodiment of the present invention, the clip circuit includes a resistor and a pair of diodes connected in parallel in opposite directions. According to this, the level of the vertical drive signal can be limited by a simple circuit, and image distortion can be prevented.

  According to the present invention, the amplitude correction of the horizontal drive signal does not become excessive due to the high voltage fluctuation, and an easy-to-view video without image distortion can be obtained on the CRT screen.

  FIG. 1 is a block diagram showing an electrical configuration of a television receiver 100 according to an embodiment of the present invention. Reference numeral 1 denotes an antenna that receives a television signal, and reference numeral 2 denotes a tuner that selects a signal having a predetermined frequency from the television signal received by the antenna 1 and converts the signal into an intermediate frequency signal for extraction. Reference numeral 3 denotes a signal processing unit for processing a signal taken out by the tuner 2, and includes a video intermediate frequency amplifier circuit, a video detector circuit, a video amplifier circuit, an audio intermediate frequency amplifier circuit, an audio detector circuit, an audio amplifier circuit, and a sync separator circuit. And other known circuits. Reference numeral 4 denotes a CRT that displays an image on a screen based on a video signal output from the signal processing unit 3.

  A vertical deflection circuit 5 receives a vertical synchronization signal output from the signal processing unit 3 and generates a vertical drive signal for vertically deflecting an electron beam in the CRT 4. This vertical drive signal is supplied to a vertical deflection coil (not shown) provided in the CRT 4 and to a horizontal amplitude correction circuit 8 described later. A horizontal deflection circuit 6 receives a horizontal synchronization signal output from the signal processing unit 3 and generates a horizontal drive signal for horizontally deflecting an electron beam in the CRT 4. This horizontal drive signal is corrected by the horizontal amplitude correction circuit 8 and applied to a horizontal deflection coil (not shown) provided in the CRT 4. The high voltage pulse output from the horizontal deflection circuit 6 is given to the flyback transformer 7. The flyback transformer 7 boosts the high-voltage pulse and applies a high voltage to the anode electrode of the CRT 4. Reference numeral 9 denotes a speaker that outputs sound based on the sound signal output from the signal processing unit 3.

  A microcomputer 10 controls the operation of the television receiver 100, and includes a CPU, a ROM, a RAM, and the like. An operation unit 11 is provided on the front panel of the television receiver 100 and includes various operation keys and switches. A display unit 12 is also provided on the front panel, and includes a LED (light emitting diode). Reference numeral 13 denotes a remote control receiver for receiving a signal transmitted from a remote controller (not shown), and 14 is an external interface for connecting an external device. A power supply unit 15 includes a power transformer and a power supply circuit, and supplies necessary power to each unit of the television receiver 100.

  FIG. 2 shows a specific example of the horizontal amplitude correction circuit 8 in FIG. In the figure, Q1 to Q3 are transistors, R1 to R15 are resistors, VR is a variable resistor (semi-fixed resistor), C1 to C4 are capacitors, D1 to D4 are diodes, and Vcc is a power supply voltage. Reference numeral 20 denotes a clip circuit that characterizes the present invention. The clip circuit 20 includes a resistor R1 and a pair of diodes D1 and D2 connected in parallel in opposite directions.

  A vertical drive signal output from the vertical deflection circuit 5 (FIG. 1) is input to the base of the transistor Q1 via the clip circuit 20, the resistor R2, and the diode D3. This vertical drive signal is a sawtooth wave as shown in FIG. A circuit composed of the transistor Q1, resistors R3 to R7, and capacitors C1 and C2 generates a correction wave for correcting the amplitude of the horizontal drive signal, that is, a horizontal correction signal, based on the input vertical drive signal. The correction signal output from the collector of the transistor Q1 is input to the base of the transistor Q2 via the variable resistor VR and the resistor R10, inverted and amplified by the transistor Q2, and then input to the base of the transistor Q3. Amplified.

  The horizontal correction signal output from the collector of the transistor Q3 has a waveform as shown in FIG. This horizontal correction signal is given to the horizontal deflection circuit 6 (FIG. 1). Based on the correction signal, the horizontal deflection circuit 6 performs correction so that the amplitude of the horizontal drive signal expands in the vicinity of the center of the screen, and supplies the corrected horizontal drive signal to the horizontal deflection coil. The correction method of the horizontal drive signal is known as described in the above-mentioned Patent Documents 1 and 2, and the present invention is not characterized by the correction itself. Will be omitted. As a result of correcting the amplitude of the horizontal drive signal as described above, the occurrence of the barrel-shaped image distortion 51 as shown in FIG. 5 is prevented. In FIG. 2, a variable resistor VR is a resistor for adjusting the level of the horizontal correction signal. In the manufacturing stage of the television receiver 100, the amplitude of the horizontal correction signal causes image distortion with respect to a predetermined reference image. The variable resistor VR is adjusted so that the value does not occur.

  Next, the operation of the clip circuit 20 which is a feature of the present invention will be described. As described above, the vertical drive signal generated by the vertical deflection circuit 5 is input to the horizontal amplitude correction circuit 8. Here, when the threshold voltage of the diodes D1 and D2 of the clip circuit 20 is equal to or lower than the normal level of the vertical drive signal applied to the diodes D1 and D2 via the resistor R1, the diodes D1 and D2 One of them is in a conductive state depending on the polarity of the.

  For this reason, when the luminance change of the screen of the CRT 4 is small, the level of the vertical drive signal is clipped to a constant level determined by the resistor R1 and the threshold voltages of the diodes D1 and D2. Then, a horizontal correction signal generated on the basis of the clipped vertical drive signal is output to the horizontal deflection circuit 6, and the horizontal drive signal is corrected in the horizontal deflection circuit 6.

  On the other hand, when the image changes from a dark image to a bright image on the screen of the CRT 4 and a sudden luminance change occurs, the beam current suddenly rises in the tube of the CRT 4 to cause a high voltage fluctuation, which causes the vertical drive signal amplitude to increase. It becomes larger than normal. However, also in this case, since the level of the vertical drive signal applied to the diodes D1 and D2 via the resistor R1 exceeds the threshold voltage of the diodes D1 and D2, the diodes D1 and D2 are in accordance with the polarity of the vertical drive signal. One of them becomes conductive. For this reason, the level of the vertical drive signal is clipped to a constant level determined by the resistor R1 and the threshold voltages of the diodes D1 and D2. Then, a horizontal correction signal generated on the basis of the clipped vertical drive signal is output to the horizontal deflection circuit 6, and the horizontal drive signal is corrected in the horizontal deflection circuit 6.

  In this way, when the clip circuit 20 is provided, the level of the vertical drive signal serving as a reference for the horizontal correction signal is always constant regardless of fluctuations in the amplitude of the vertical drive signal. Therefore, if the variable resistor VR is adjusted so as not to cause image distortion with respect to the clipped vertical drive signal at a certain level, the horizontal correction is performed even if the amplitude of the vertical drive signal increases due to a change in the luminance of the image. The amplitude of the signal is maintained at a constant value, that is, a value adjusted by the variable resistor VR. Accordingly, it is possible to avoid the occurrence of image distortion due to an excessive correction due to an increase in the amplitude of the horizontal correction signal.

  FIG. 3 shows the waveform of the vertical drive signal at point A in FIG. If the level of the vertical drive signal is increased due to a change in the luminance of the video, if the clip circuit 20 is not provided, the vertical drive signal has a waveform with a large amplitude Y1 as shown in FIG. On the other hand, when the clip circuit 20 is provided as in the present invention, the vertical drive signal has a waveform in which the amplitude Y2 is limited to a constant value as shown in FIG.

  FIG. 4 shows the waveform of the horizontal correction signal at point B in FIG. FIG. 4A shows a horizontal correction signal generated based on the vertical drive signal shown in FIG. 3A when the clip circuit 20 is not provided, and has a waveform with a large amplitude Z1. On the other hand, FIG. 4B is a horizontal correction signal generated based on the vertical drive signal of FIG. 3B when the clip circuit 20 is provided, and a waveform in which the amplitude Z2 is limited to a constant value. Become.

  By providing the clip circuit 20 in the horizontal amplitude correction circuit 8 in this way, when the image on the screen of the CRT 4 is switched from a dark image to a bright image, a high voltage fluctuation occurs due to an increase in the beam current, and the vertical drive signal Is increased by the clip circuit 20, and the level of the vertical drive signal is suppressed to a constant value. Accordingly, the amplitude of the horizontal correction signal generated based on the vertical drive signal is also limited to a constant value, so that the horizontal deflection circuit 6 does not excessively correct the amplitude of the horizontal drive signal, and on the screen of the CRT 4. An easy-to-view video without image distortion can be obtained.

  In order to eliminate high voltage fluctuations due to changes in screen brightness, it may be possible to take measures against the power supply circuit. In this case, however, a complicated circuit for stabilizing the voltage against a sudden increase in the beam current. Will be required, leading to an increase in cost. However, if the clip circuit 20 including the resistor R1 and the diodes D1 and D2 is provided to limit the level of the vertical drive signal as in the present embodiment, the power supply circuit can be simplified without any modification. By adding a simple circuit, image distortion can be prevented and costs can be reduced.

  In the embodiment described above, the clip circuit 20 includes the resistor R1 and the diodes D1 and D2. However, the present invention is not limited to this, and an element such as a Zener diode can be used instead of the diode. . Further, the clip circuit 20 may be configured using a transistor.

  In the above-described embodiment, the circuit of FIG. 2 is exemplified as the horizontal amplitude correction circuit 8 that generates the horizontal correction signal. However, the horizontal amplitude correction circuit 8 may be other circuits. For example, although a variable resistor VR for adjusting the level of the horizontal correction signal is provided in FIG. 2, the present invention can be applied to a horizontal amplitude correction circuit that does not include the variable resistor VR. There is an effect that image distortion can be suppressed by limiting the level.

  Further, in FIG. 1, a single unit is exemplified as the television receiver 100, but the present invention is also applicable to a composite television receiver incorporating a DVD (Digital Versatile Disk) recorder, a video deck, or the like. be able to.

It is the block diagram which showed the electrical constitution of the television receiver which concerns on embodiment of this invention. It is a figure which shows the specific example of a horizontal amplitude correction circuit. It is a waveform diagram of a vertical drive signal. It is a wave form diagram of a horizontal correction signal. It is a figure which shows barrel-shaped image distortion.

Explanation of symbols

4 CRT
DESCRIPTION OF SYMBOLS 5 Vertical deflection circuit 6 Horizontal deflection circuit 8 Horizontal amplitude correction circuit 20 Clip circuit 100 Television receiver Q1-Q3 Transistor R1-R15 Resistance VR Variable resistance C1-C4 Capacitor D1-D4 Diode

Claims (2)

CRT (Cathode Ray Tube) for displaying video,
A vertical deflection circuit for generating a vertical drive signal for vertically deflecting an electron beam applied to the screen of the CRT;
A horizontal deflection circuit for generating a horizontal drive signal for horizontally deflecting an electron beam applied to the screen of the CRT;
A horizontal amplitude correction circuit for generating a horizontal correction signal for correcting the amplitude of the horizontal drive signal based on the vertical drive signal;
A variable resistor for adjusting the level of the horizontal correction signal,
In a television receiver that corrects image distortion occurring at both ends of the screen of the CRT by correcting the amplitude of a horizontal drive signal with the horizontal correction signal,
The horizontal amplitude correction circuit is provided with a clip circuit that limits the amplitude of the vertical drive signal to a constant value, and the clip circuit includes a resistor and a pair of diodes connected in parallel in opposite directions,
The television receiver, wherein the variable resistor is adjusted so as not to cause image distortion with respect to a vertical drive signal of a certain level clipped by the clipping circuit. CRT (Cathode Ray Tube) for displaying video,
A vertical deflection circuit for generating a vertical drive signal for vertically deflecting an electron beam applied to the screen of the CRT;
A horizontal deflection circuit for generating a horizontal drive signal for horizontally deflecting an electron beam applied to the screen of the CRT;
A horizontal amplitude correction circuit for correcting the amplitude of the horizontal drive signal based on the vertical drive signal,
In a television receiver configured to correct image distortion occurring at both ends of the screen of the CRT by correcting the amplitude of a horizontal drive signal by the horizontal amplitude correction circuit,
A television receiver comprising a clip circuit for limiting an amplitude of the vertical drive signal to a constant value in the horizontal amplitude correction circuit.

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