JPH0119495Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is generally applicable to television receivers that can change the aspect ratio of the screen regardless of the standard method of television broadcasting. The present invention relates to a television receiver which prevents the current density on a cathode ray tube from becoming excessive when the current density is switched to be smaller.

[Conventional technology]

Generally, television signals for ordinary television broadcasting are determined in accordance with a standard system so that the aspect ratio of the screen on a cathode ray tube is 3:4. However, cable television and home VTRs
For personal and home purposes such as, it is possible to appropriately select and use a specific television signal, so the aspect ratio of the screen can be changed regardless of the general standard system.

[The problem that the idea aims to solve]

However, in special television receivers for such special uses, if the raster aspect ratio is changed without changing the drive adjustment circuit including the brightness adjustment circuit of the cathode ray tube, the current density on the cathode ray tube changes. It may become excessive. For example, when a television receiver receives a special television signal with a large screen, the aspect ratio is 1:1 as shown in Figure 1.
2.35, but when it comes to receiving normal television signals, the aspect ratio becomes 1:1.
1.33, and the current density on the cathode ray tube suddenly becomes
This will result in an increase of 1.77 times. In such a case,
Although a high-brightness image can be obtained, the image quality deteriorates, and burn-in occurs particularly in the center of the phosphor, which accelerates the deterioration of the cathode ray tube.

The present invention was developed in view of these conventional problems.In particular, when switching the aspect ratio of the screen on a cathode ray tube, the constants of the drive adjustment circuit of the cathode ray tube, including brightness adjustment, and the automatic brightness limiting circuit are linked. By switching the current density on the cathode ray tube, it is possible to prevent the current density on the cathode ray tube from becoming excessive.
It is an object of the present invention to provide a television receiver which prevents color unevenness caused by burn-in of phosphors.

[Means to solve the problem]

In order to solve the above problems and achieve the above objectives,
The television receiver according to the present invention switches and controls an aspect ratio switch that switches the output of the horizontal deflection circuit or the vertical deflection circuit, depending on the identification signal detected by the signal detection circuit that detects the identification signal in the input video signal. It is a television receiver that switches the aspect ratio of the screen on a cathode ray tube, and includes a brightness adjustment circuit, a contrast adjustment circuit, an amplifier circuit whose passband is the frequency of the chromaticity signal, and an automatic brightness adjustment. Each of the circuits is equipped with a constant changeover switch that switches and sets the constant of the circuit, and by controlling each of the above constant changeover switches according to the identification signal detected by the signal detection circuit, it is possible to switch between the CRT and the CRT when changing the screen aspect ratio. The present invention is characterized in that switching is performed to prevent the upper current density from becoming excessive and to prevent deterioration of image quality.

[Effect]

In the television receiver according to the present invention,
When changing the aspect ratio of the screen on the cathode ray tube,
The constants of the brightness adjustment circuit, the contrast adjustment circuit, the amplifier circuit whose pass band is the frequency of the chromaticity signal, and the automatic brightness limit circuit are switched in conjunction with each other, so that the current density on the cathode ray tube is prevented from becoming excessive. .

〔Example〕

FIG. 2 shows a circuit of a television receiver according to the present invention. Here, 1 is a terminal for inputting a video signal from a video amplification circuit, etc., and a low-pass filter 2, a contrast adjustment circuit 3, and a brightness adjustment circuit 4 are connected to this one after another. A matrix circuit 5 for extracting primary color signals from the signals is connected. A contrast adjustment variable resistor 6 is connected to the contrast adjustment circuit 3, which is grounded via a contrast voltage setting resistor 7. Reference numeral 8 denotes a constant changeover switch that is used to change the aspect ratio of the screen, and is composed of a fixed contact 8a for normal mode, a fixed contact 8b for wide mode, and a movable contact piece 8c. It is connected to the connection midpoint, and the movable contact piece 8c is grounded. Further, a variable resistor 9 for adjusting brightness is connected to the brightness adjusting circuit 4, and this is grounded via a resistor 10 for setting a brightness voltage. 11 is a constant changeover switch that changes when the screen changes as described above;
It consists of a fixed contact 11a for normal, a fixed contact 11b for wide, and a movable contact piece 11c.The fixed contact 11a is connected to the midpoint between the variable resistor 9 and the resistor 10, and the movable contact 11c is grounded. There is. Note that each of the fixed contacts 8b and 11b described above is an idle contact.

On the other hand, the matrix circuit 5 is connected to the terminal 1 via a band amplification circuit 12 and a color demodulation circuit 13, respectively, and cathodes 15a, 15b, 15c of a cathode ray tube 14 are connected to the output side of the matrix circuit 5. A chromaticity adjustment circuit 16 is connected to the band amplification circuit 12 described above. This is variable resistor 1
7 is connected in series with a resistor 18 and grounded, and a constant changeover switch 19 is connected to the fixed contact 19a of the constant changeover switch 19 for normal use.
is connected to the midpoint between the variable resistor 17 and the resistor 18, and the other fixed contact 19b becomes an idle contact.
Moreover, the movable contact piece 19c is grounded.

Further, a synchronization separation circuit 20 is connected to the terminal 1, and a vertical deflection circuit 21 and a horizontal deflection circuit 22 are connected to one output side of the synchronization separation circuit 20, and a vertical deflection coil 23 and a horizontal deflection coil 24 of the cathode ray tube 14 are connected to these. It is connected. A voltage dividing resistor 2 for current adjustment is connected to the horizontal deflection circuit 22 via the emitter of a transistor 25 for horizontal output adjustment.
6, 27, and 28 are connected, and a fixed contact 29a for normal mode and a fixed contact 29b for wide mode of aspect ratio changeover switch 29 are connected to the middle points of these connections, and movable contacts selectively connected to these are connected. A contact piece 29c is connected to the base of the transistor 25. The horizontal synchronization signal of the synchronization separation circuit 20 is also input to a high voltage output circuit 30, and a high voltage rectifier circuit 32 and an automatic brightness limiting circuit 33 are connected to the secondary side of a flyback transformer 31 connected thereto. The high-voltage rectifier circuit 32 is connected to the anode electrode of the cathode ray tube 14, and the contrast adjustment circuit 3, brightness adjustment circuit 4, and band amplification circuit 12 are connected to the automatic brightness limiting circuit 33, respectively. In addition, this automatic brightness limit circuit 3
3 is also connected, as shown, to a constant changeover switch 34 having a movable contact piece 34c that can be selectively switched to a fixed contact 34a for normal mode and a fixed contact 34b for wide mode.

35 is a signal detection circuit that detects an identification signal connected to the terminal 1, and when a special television signal with a screen aspect ratio different from that of a general television signal is received, extracts the identification signal. This signal detection circuit 35
is connected to a relay 36 which operates according to the detection output of the identification signal, and depending on the operation of this relay 36, each of the above-mentioned changeover switches 8, 11, 19, 29,
34 movable contact pieces 8c, 11c, 19c, 29c,
34c is the wide fixed contact 8b, 11b,
Connected to 19b, 29b, and 34b. Note that, as the above-mentioned identification signal, a sine wave, a rectangular wave, etc. superimposed on the top of the horizontal synchronizing signal or the video signal of the first several H periods of the vertical scanning period is used.

In a circuit with such a configuration, when a normal broadcast television signal is being received, the television signal is separated into a video signal including a synchronization signal and an audio signal, and then the video signal is sent to a video signal amplifier. It is then supplied to the cathode ray tube. That is, the video signal input to the input terminal 1 is supplied to the matrix circuit 5 via a low-pass filter 2, a contrast adjustment circuit 3, and a brightness adjustment circuit 4, and is also supplied to a separate band amplifier circuit 12 and a color demodulation circuit. It is input to the matrix circuit 5 through the circuit 13, and is applied to each cathode 15a, 1 of the cathode ray tube 14.
Video signals are input to 5b and 15c. On the other hand, the video signal input to the input terminal 1 is sent to the sync separation circuit 20, where the sync signal is separated and taken out.
The sawtooth wave outputs are input to a vertical deflection circuit 21 and a horizontal deflection circuit 22, and their respective sawtooth outputs are input to a vertical deflection coil 23 and a horizontal deflection coil 24, and a screen with a normal aspect ratio of 1:1.33 is reproduced on the cathode ray tube 14. It works like this. Further, the output of the synchronous separation circuit 20 is input to a high voltage output circuit 30 and a flyback transformer 31, and the high voltage output is input to a high voltage rectifier circuit 3.
After being rectified at step 2, the signal is input to the anode electrode of the cathode ray tube 14. Thus, CRT 1
4, a normal television image with an aspect ratio of 1:1.33 is reproduced. On the other hand, automatic brightness limiting circuit 33
The signal applied to the display 30 acts to prevent excessive current from flowing through the cathode ray tube, overloading the high-voltage output circuit 30, and destroying the horizontal output transistors and the like when the brightness becomes abnormally high.
The signal applied to this automatic brightness limiting circuit 33 is
A function of detecting a change in the output current of the flyback transformer 31 and feeding back the detected output to the contrast adjustment circuit 3, brightness adjustment circuit 4 and band amplification circuit 12, respectively, to limit the beam current of the cathode ray tube to below a specified value. doing.

On the other hand, when a special television signal such as a cable television broadcast or a VTR is received, the identification signal included in the signal is detected by the signal detection circuit 35, so the relay 36 is activated. . Therefore, the movable contacts 8c, 11c, 19c, 29c, 34c of the changeover switches 8, 11, 19, 29, 34 driven by this are fixed contacts 8b, 11b, 19 for wide, respectively.
b, 29b, and 34b, respectively.
That is, by switching the aspect ratio switch 29, the horizontal deflection circuit 2 passes through the transistor 25.
The current applied to 2 increases and is input to the horizontal deflection coil 24, increasing the horizontal amplitude of the screen on the cathode ray tube and expanding the aspect ratio.
Also, at this time, each of the constant changeover switches 8, 1
Since the control potentials 1, 19, and 34 also rise, the matrix circuit 5 connected to each output side of the contrast adjustment circuit 3, brightness adjustment circuit 4, and band amplification circuit 12 increases the current density of the cathode ray tube 14. act. In this way, even if the aspect ratio of the screen is enlarged to, for example, 1:2.35, a bright image can be obtained that is the same as when receiving normal television broadcasts.

Further, when receiving normal television broadcasting, there is no identification signal and this is not detected by the signal detection circuit 35, so the relay 36 does not operate and the changeover switches 8, 11, 19,
29, 34 movable contact pieces 8c, 11c, 19c,
29c, 34c are fixed contacts 8a, 11a, 19
a, 29a, and 34a. Therefore, the matrix circuit 5 acts to lower the current density of the cathode ray tube 14. This prevents the phosphor of the cathode ray tube from burning in, thereby preventing color unevenness from occurring. Furthermore, the generation of X-rays due to high brightness is suppressed, and a decrease in the luminous efficiency of the central part of the phosphor due to a rise in the temperature of the panel surface and a collapse of the white balance are prevented. Optimal contrast adjustment and chromaticity adjustment are performed to prevent deterioration in image quality.

The output of the horizontal deflection circuit or the vertical deflection circuit is switched by switching the base potential of an output adjusting transistor provided at the front stage of the circuit by means of switching means. Therefore, it is not affected by the impedance of the horizontal or vertical deflection coil.
The amplitude of deflection can be accurately controlled, and furthermore, the design and manufacturing adjustments for each of the above-mentioned deflection coils are facilitated.

[Effect of idea]

As described above, according to the present invention, the identification signal is detected by a signal detection circuit that detects the identification signal inserted in a special television signal whose screen aspect ratio is different from that of a general television signal. Depending on the identification signal detected by the signal detection circuit,
The aspect ratio switching switch that changes the output of the horizontal deflection circuit or the vertical deflection circuit is controlled so that the aspect ratio of the screen on the cathode ray tube can be changed. The brightness adjustment circuit, the contrast adjustment circuit, the amplification circuit whose pass band is the chromaticity signal, and the automatic brightness limiting circuit are each equipped with a constant changeover switch for switching and setting the constant of the circuit.
The switching of each of these constant changeover switches is controlled depending on the identification signal detected by the signal detection circuit.

Therefore, when the aspect ratio of the screen is reduced, the current density on the cathode ray tube is suppressed, and this current density is prevented from becoming excessive, thereby preventing color unevenness due to phosphor burn-in and X-ray The occurrence of such problems is prevented. Moreover, the white balance is prevented from being distorted due to the temperature of the panel surface rising and the luminous efficiency of the phosphor being reduced only in the center. moreover,
Since optimal contrast adjustment and chromaticity adjustment are performed in accordance with the aspect ratio of the screen, deterioration in image quality due to switching of the aspect ratio of the screen is prevented.

Furthermore, since the current density on the cathode ray tube is automatically suppressed by detecting the identification signal, there is no need for complicated switching operations. Since the normal aspect ratio corresponding to the type is maintained, there is no risk that the current density will be excessive or that the image quality will deteriorate due to erroneous operation. In other words, the brightness adjustment circuit when the aspect ratio of the screen is reduced,
Switching control of the contrast adjustment circuit, amplifier circuit, and automatic brightness limiting circuit is reliably performed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the different aspect ratios of the screen of a cathode ray tube. FIG. 2 is a circuit diagram showing the connections between the circuits constituting the cathode ray tube drive adjustment circuit and the automatic brightness limiting circuit in the television receiver of the present invention. 1... Video signal input terminal, 2... Low pass filter, 3... Contrast adjustment circuit, 4... Brightness adjustment circuit, 5... Matrix circuit, 8, 1
1, 19, 34...Constant selection switch, 29...
Aspect ratio switch, 12...Band amplifier circuit, 1
4... Braun tube, 20... Synchronous separation circuit, 2
3, 24...Deflection coil, 35...Signal detection circuit, 36...Relay.

Claims (1)

[Claims for Utility Model Registration] Controlling an aspect ratio changeover switch that switches the output of a horizontal deflection circuit or a vertical deflection circuit depending on an identification signal detected by a signal detection circuit that detects an identification signal in an input video signal, A television receiver configured to switch the aspect ratio of a screen on a cathode ray tube, comprising a brightness adjustment circuit, a contrast adjustment circuit, and an amplifier circuit whose passband is the frequency of a chromaticity signal.
The automatic brightness adjustment circuit is equipped with a constant changeover switch that changes and sets the constant of each circuit, and the screen aspect ratio can be changed by controlling the above constant changeover switches according to the identification signal detected by the signal detection circuit. A television receiver that performs switching to prevent the current density on the cathode ray tube from becoming excessive when switching and to prevent deterioration of image quality.