KR830000269B1 - Luminance control circuit for a television receiver - Google Patents

Abstract

In a television receiver, the luminance control cct. having black level detect means(10a,30c,30d) produces a control signal in response to a video signal exceeding an end of the dynamic range of a cathode ray tube(13). Gain control ccts. in the path of the video signal to the cathode ray tube adjust their gain in response to the control signal to maintain the video signal within the dynamic range of the cathode ray tube. The end of the dynamic range at which the video signal may be controlled includes one or both of the white peak and black levels. The control signal may be responsive to an average cathode ray tube beam current exceeding a predetd. value.

Description

Automatic brightness control device of television receiver

1 and 5 are diagrams for explaining the present invention, respectively.

2 and 3 are diagrams each showing an example of an automatic brightness adjusting device of a conventional television receiver.

4 is a configuration diagram showing an example of an automatic brightness adjustment device of a television receiver of the present invention.

6 is a connection diagram showing a specific example of FIG.

7, 10 and 11 are diagrams each showing another embodiment of the present invention.

8 is a configuration diagram showing an example of a television receiver.

FIG. 9 is a diagram for explaining FIG.

12 is a diagram for explaining the operation of the automatic pedestal level adjustment circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

1: luminance signal input terminal 7: chromatic signal input terminal

10 12: Gain control circuit 11: Video output circuit

13: color cathode ray tube 14: OR circuit

15: beam current detection circuit

The present invention relates to a device for automatically adjusting brightness of a television receiver, and in particular, to effectively reproduce the transmission signal by utilizing the limited expressive ability of the cathode ray tube.

In general, as shown in FIG. 1, the operating point of the video signal is determined by the point P, which is determined by the cut-off characteristic of the cathode ray tube, and the point R, which is as high as the size of the electron beam shape is visually acceptable. As shown in FIG. 1, the lump level (pedestal level) of the video signal is associated with point P, and the white peak level W is associated with point R. As shown in FIG. The expression ability of a cathode ray tube is determined by this range between P point and R point, and the back peak level W is corresponded to R point. The range between the P point and the R point determines the expressive power with the cathode ray. In this case, the wider the range between the P point and the R point, the better the expressive power is.

In addition, when the average beam current in the cathode ray tube exceeds the prescribed value, irrationality such as breaking the high voltage circuit or damaging the phosphor of the cathode ray tube occurs, so it is necessary to control the average value M of the video signal.

Therefore, the following three points are important for obtaining excellent image expression in cathode ray tubes.

(1) The black level in the video signal should always match the P point.

(2) The back peak level in the video signal should always be kept within R point.

(3) Maximum output is obtained so that the average impeding current does not exceed a predetermined current.

In addition, the transmission video signal cannot always be a correct signal, and it cannot be said that the transmission video signal matches the expression capability of the cathode ray tube of each television receiver. It is desirable to be able to sufficiently express the poor quality of the transferred new video signal.

As a circuit for determining the back peak level of a video signal supplied to a conventional color cathode ray tube, one as shown in Figs. 2 and 3 has been proposed. That is, in Fig. 2, reference numeral 1 denotes a luminance signal input terminal supplied with the luminance signal Y, and the luminance signal Y supplied to the luminance signal input terminal 1 is converted into the luminance signal amplifying circuit 2 and the luminance signal Y. Through the limiter circuit 3 which limits the peak value to a predetermined value, it is supplied to the base of the PNP type transistor 4 constituting the matrix circuit, the collector of the transistor 4 is grounded, and the emitter of the transistor 4 is grounded. Are connected to the respective emitters of the NPN transistors 6a, 6b, and 6c through the variable resistors 5a, 5b, and 5c for adjusting the drive amount, respectively, and these transistors 6a, RY signal input to which a color difference signal RY signal, a GY signal, and a BY signal (where R is a red signal, G is a green signal, and B is a blue signal) are supplied at respective bases of (6b) and (6c), respectively. A terminal 7R-Y and a BY signal input terminal 7B-Y are derived, and these transistors 6a, 6b and 6C are obtained. R signal output terminal (8R), G signal output terminal (8G) and B signal output terminal (8B) are respectively derived from the respective collectors of < RTI ID = 0.0 >). ≪ / RTI > The R signal, the G signal and the B signal obtained at the B signal output terminal 8B are respectively supplied to the color cathode ray tube. In FIG. 1, the peak value of the luminance signal Y is limited by the limiter circuit 3 to limit the back peak level of the video signal supplied to the color cathode ray tube. In FIG. 1, one limiter circuit using one diode is used to limit the back peak level of the video signal. However, when the signal levels of the RY signal, the GY signal, and the BY signal of the color difference signal are large, these color difference signals are applied. Since the level of the video signal supplied to the color cathode ray tube is determined, the peak level of the signal is not limited at this time.

As a supplement to the drawback of FIG. 2, a circuit as shown in FIG. 3 can be considered. In FIG. 3, the luminance signal Y supplied to the luminance signal input terminal 1 is supplied to the base of the transistor 4 through the luminance signal amplifying circuit 2, and the three transistors 6a, 6b and Each collector of 6C is connected to the positive electrode of the battery 9 set to a predetermined value through diodes 3a, b and 3C constituting the limiter circuit, respectively. The negative electrode of () is grounded, and the other part is comprised similarly to FIG. In FIG. 3, since the peak shape of the R signal, the G signal, and the B signal obtained on each collector side of the transistors 6a, 6b, and 6C is limited, even if the level of the color difference signal is large, the problem is large. Although the drive amount of the R signal, the G signal, and the B signal is changed by the drive adjustment by the variable resistors 5a, 5b, and 5C, the color of the peak signal becomes a different color. This asking fault occurs.

In view of this point, the present invention eliminates the above-mentioned defects and effectively reproduces the transmission signal by effectively utilizing the limited expressive ability of the cathode ray tube. Next, an example in which the automatic brightness adjusting device of the television receiver of the present invention is applied to a color television receiver will be described with reference to FIG. In FIG. 4, the luminance signal Y supplied to the luminance signal input terminal 1 is included through a gain control circuit 10, including a color demodulation circuit, a matrix circuit, an image signal amplifying circuit, and the like. And the chroma signal supplied from the chroma signal input terminal 7 to the chroma signal input terminal of the image output circuit 11 through the gain control circuit 12. The R, G, and B signals obtained on the output side of 11) are supplied to the red, green, and blue cathodes 13R, 13G, and 13B of the color tone tube 13, respectively. In this example, the R, G, and B signals supplied to the red, green, and blue cathodes 13R, 13G, and 13B of the color cathode ray tube 13 are each OR circuit 14. Supplies the first, second, and third input terminals of the first, second, and third input terminals, and outputs the output signal obtained at the output terminal of the OR circuit 14 to the beam current detection circuit 15. Detects an error from the reference value of the cathode current, generates a gain control signal corresponding to the detection output, and obtains a gain control signal obtained on the output side of the beam current detection circuit 15 by the gain control circuit 10 and Each control signal input terminal (12) is supplied to provide the amplitude of the luminance signal Y and the chroma signal. In this case, the back peak level of the video signal is set to the R point of the characteristic as shown in FIG. 1 of the color cathode ray tube 13.

As described above, according to the present invention, since the beam current of the color cathode ray tube 13 is directly detected and the amplitude of the video signal is controlled by this detection output, it is always possible to obtain the most suitable expression ability of the cathode ray tube 13. . That is, even if the beam current caused by the video signal supplied to the cathode ray tube 13 is larger than the cathode current I _{P at the} point P of FIG. 1 as shown in FIG. 5A, as shown in FIG. This beam current becomes a current between the current I _{P at} point _P and the current I _R at point _{R in} FIG. 1, and the transmission signal can be reproduced by effectively utilizing the limited expressive power of the cathode ray tube 13. In this example, the R signal, the G signal, and the B signal are taken and detected, thereby controlling the amplitude of the luminance signal and the chromaticity signal, so that it is not affected by drive adjustment, nonuniformity of cathode ray tube characteristics, and the like. Colors are not colored on the back peak, so that even if the levels of the three color difference signals are different, an accurate limit point can be secured at all times.

6 shows a specific circuit of the beam current detection circuit 15 in FIG. In Fig. 6, parts corresponding to Fig. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

R signal input terminal, G signal input terminal and B signal input terminal supplied with the R signal, G signal and B signal from the matrix circuit, and these R signal, G signal and B signal input terminals 16R, 16R. And the R, G and B signals supplied to the 16B are supplied to respective bases of the NPN transistors 17R, 17R, and 17B constituting the image output amplifier circuit, respectively, and these transistors 17R. ), (17R) and (17B), respectively, are connected to a power supply terminal 19 to which a positive DC voltage is supplied through resistors 18R, 18R, and 18B, respectively. Collectors of the transistors 17R, 17R, and 17B, respectively, of the bases of the NPN transistors 20R, 20R, and 20B, and the NPN transistors 21R, 21R, and 21B, respectively. Connected to the respective bases, the respective emitters of these transistors 20R, 20R, and 20B and the respective emitters of transistors 21R, 21G, and 21B are slowed down, and these Each collector of transistors 20R, 20R, and 20B is connected to a power supply terminal 19, and each collector of these transistors 21R, 21G, and 21B is used for current detection, respectively. Ground through resistors 22R, 2G, and 22B, and each emitter and junction of transistors 20R and 21R, and each of emitters with transistors 20G and 21G, respectively. The connection point and the connection point of each emitter of the transistors 20B and 21B are respectively connected to the cathodes 13R, 13G, and 13B for the red, green, and blue colors of the color cathode ray tube 13, respectively. . In this example, the collectors of the transistors 21R, 21G, and 21B are differentially configured through the diodes 14R, 14G, and 14B, which constitute the OR circuits 14, respectively. Connected to the base of one of the NPN transistors 15a constituting the beam current detection circuit 15, and the base of the transistor 15a is memorized through the capacitor 15c to emit the emitter of the transistor 15a. Is connected to the emitter of the other NPN transistor 15b, the connection point of each emitter of these transistors 15a and 15b is grounded through the constant current circuit 15d, and the other transistor ( The base of 15b) is grounded through the battery 15e for obtaining the reference voltage _VREF , and is placed between the control signal output terminals 15f and 15g derived from the respective collectors of these transistors 15a and 15b. The obtained control signal is input to the control signal input terminals of the gain control circuits 10 and 12, respectively. It should be supplied. In this case, when the limit current Is max is the resistance value of each of the resistors 22R, 22G, and 22B, R,

Is max = *** is determined.

7 shows an example in which the present invention is combined with an average automatic luminance limiting circuit (hereinafter referred to as an ABL circuit). In FIG. 4, parts corresponding to those of FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

In Fig. 7, reference numeral 23 denotes a horizontal output circuit. The output signal of the horizontal output circuit 23 is supplied to the primary winding 24a of the flyback transformer 24, and the flyback transformer 24 is provided. Is connected to the anode electrode 13a of the color cathode ray tube 13 through the high-voltage rectifier circuit 25, and the secondary winding 24b of the flyback transformer 24 is connected to one end of the secondary winding 24b. The other end of the circuit is grounded through a parallel circuit of the variable resistor 26 and the capacitor 27 constituting the average beam current detection circuit of the average value ABL circuit, and the connection point of the secondary winding 24b and the variable resistor 26 is grounded. It is connected to the other input terminal of the OR circuit 29 through a threshold circuit 28 which is to generate a control signal when the average current reaches a set value. The output side of the circuit 15 is connected to one input terminal of the OR circuit 29, and the control signal obtained at the output side of this OR circuit 29 is gained. Respectively, to supply a control signal input terminal of the control circuit (10) and (12). The other part is comprised similarly to FIG.

As shown in FIG. 7, the average value and peak value of the beam current of the cathode ray tube are suppressed by combining the present invention and the average value ABL Hi, so that the ability to express the image signal is always automatically displayed even when any image signal arrives. It can be changed to best suit the expressive power of. In addition, in the case of FIG. 7, in the case where it is desired to change the expression range, the variable resistor 26 in the ABL circuit may be adjusted to change the feedback voltage or the threshold voltage of the threshold circuit 28 may be changed. Setting the threshold voltage of the 26 and threshold circuit 28 to the full range makes the setting completely automatic. In FIG. 7, a DC amplifier circuit is provided on the output side of the gain control circuit 10 so that the gain of the DC amplifier circuit is controlled by the output signal of the threshold circuit 28 to control the DC level of the video signal. Of course, you may.

In general, although the black level in the video signal to be transmitted is determined as the set-up level, it is not always possible to send correctly, so it is often desirable to make the darkest part of the video signal black. In addition, by automatically setting the black level, the expression ability of the cathode ray tube can be further increased. As an automatic black level adjusting device for a color television set that satisfies such a requirement, the one shown in FIG. 8 can be considered. In FIG. 8, parts corresponding to FIGS. 3 and 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

That is, one input terminal 31 of the addition circuit 30a constituting the automatic pedestal circuit 30 carries out the luminance signal as shown in the curve 1a of FIG. 9A supplied to the luminance signal input terminal 1. ), This reverse blanking signal is supplied to the other input terminal of the addition circuit 30a. In this case, at the output of the addition circuit 30a, a signal is obtained in which the blanking period as shown in FIG. 9B in which the inverse blanking signal is interspersed in the blanking period of the video signal is the intermediate level of the video signal. Through 30b, it is supplied to the input side of the luminance signal amplifying circuit 2, and is supplied to the base of this addition circuit 30a. The collector of this transistor 30c is connected to a power supply terminal + B to which a positive DC voltage is supplied, and the emitter of this transistor 30c is grounded through a capacitor 30d constituting a negative peak detection circuit. The emitter of the transistor 30c is connected to the base of the NPN type transistor 30e, the collector of this transistor 30e is connected to the power supply terminal + B, and the emitter is connected to the transistor 30e. Grounded through, the emitter of the transistor 30e is connected to the connection point of the emitter of the NPN type transistor 30g constituting the switching circuit and the collector of the NPN type transistor 30h, and the transistor on the output side of the switching circuit ( The connection point of the collector of 30g) and the emitter of transistor 30h is connected to the input side of the luminance signal amplifying circuit 2, and each base of these transistors 30g and 30h is connected to the reverse blanking signal input terminal. And it has a switching circuit formed of a transistor (30g) and (30h) of only the blanking period of the video signal. Since the automatic pedestal setting circuit 30 is configured as described above, the pedestal level of the video signal is negatively applied to the source side, that is, the input side of the luminance signal amplifying circuit 2 as shown in FIG. A signal equal to the negative maximum level of the signal in the direction, i.e., the video signal having the darkest part of the video signal as the pedestal level or the black level is obtained.

The output signal of the luminance signal amplifying circuit 2 is supplied to the base of the transistor 4, and the signals obtained by the emitters of the transistor 4 are supplied to the variable resistors 5a, 5b, and (for driving adjustment), respectively ( 5c) is connected to the respective emitters of the transistors 6a, 6b, and 6c constituting the matrix circuit, and is connected to the RY signal input terminals 7R-Y and GY signal input terminals 7G-Y. ) And BY signal input terminals 7B-Y are connected to respective bases of the transistors 6a, 6b, and 6c through the amplifying circuits 32a, 32b, and 32c, respectively, Each collector of the transistors 6a, 6b, and 6c will be described only for the output circuit 33B including the automatic black level adjustment device. In other words, in this example, the collector of transistor 6C is connected to power supply terminal 19 via resistor 18B, and the collector of transistor 6C is connected to each of NPN transistor 20B and PNP transistor 21B. Is connected to the base of the transistor 20B, the collector of this transistor 20B is connected to the power supply terminal 19, and the respective emitters of the transistors 20b and 21b are connected to each other, and the transistors 20B and 21B are connected. The connection point of each emitter of is connected to the blue cathode 13B of the color cathode ray tube 13. In addition, the collector 21 of the transistor 21B is grounded through the constant current source 43 of the hob level current IB to be set by the video signal, and a connection switch 35 is provided between both ends of the constant current source 34. (35) is " off " only in the horizontal blanking period. 35a is a control signal input terminal supplied with a control signal synchronized with the horizontal blanking period. In this case, the video signal obtained on the collector side of the transistor 6C removes the horizontal synchronous signal H as shown in FIG. In addition, the collector of the transistor 21B is connected to the base of the NPN transistor 36, the emitter of the transistor 36 is grounded, and the collector of the transistor 36 forms a low-pass filter constituting a memory circuit. Connect to the input side. The output signal of this low-pass filter 37 is used as a gain control signal, and is supplied to the amplifier circuit 32C. In the automatic black level adjustment device of the output circuit 33B, the normal video signal period connecting switch 35 is "on" and the constant current source 34 is shorted, so that the transistor 21B performs an emitter follower operation. As in the normal television receiver, the anode current of the cathode ray tube 13 flows through the transistor 21B and the connection switch 35 to the ground. When the connection switch 35C is turned "off" during the horizontal blanking period, the anode current of the cathode ray tube 13 determined by the pedestal level corresponding to the collector potential of the transistor 6C becomes the transistor 21B. Flows out of the collector, but if it is set larger than the constant current IB of the constant current source 34 corresponding to the black level current, a large current flows into the base of the transistor 36, which is a low pass filter 37. Since it is fed back to the amplification circuit 32C, the collector voltage of the transistor 6C is controlled until the anode current of this cathode ray tube 13 is equal to IB, and the black level current is automatically controlled. Adjust black level current automatically. In this case, the video signal period is continuously controlled by the control signal stored by the low pass filter 37, so that the black level of the video screen can be adjusted automatically.

Therefore, as shown in FIG. 8, the pedestal level can be set at the signal level corresponding to the black peak of the video signal, and the black level can be secured automatically.

FIG. 10 is a combination of FIG. 7 and FIG. 8 according to the present invention. In FIG. 10, parts corresponding to FIGS. 6, 7, and 8 are denoted by the same reference numerals. Detailed description will be omitted. In FIG. 10, 11a is a color tone circuit. Other than that is the same as FIG. 7 and FIG. 8, In this FIG. 10, the effect of FIG. 7 and FIG. 8 can be acquired simultaneously. Therefore, it is possible to maximize the expressive ability of cathode ray tube which black level and white level are used for any transmitted video signal, so that no black breakdown or white breakage occurs and a good white balance is secured. There is a benefit that there is no need to eliminate the need for brightness and contrast adjustment. In other words, as shown in FIG. 5A, when the input video signal exceeds the range of points P to R in FIG. 1, the video signal is compressed to be in the range of P to R points as shown in FIG. In addition, as shown in FIG. 5C, the input video signal has the effect of being in the range of P to R points.

11 is a combination of the fourth example and the eighth example according to the present invention. In FIG. 11, reference numeral 11a denotes a color-color inquiry, and 11b denotes an image including a matrix circuit, an image signal amplification circuit, and the like. The output circuits 33Ra, 33Ra, and 33Ba respectively represent only the automatic black level adjusting devices of the output circuits 33R, 33G, and 33B in FIG. 8, respectively. Others are similar to those of Figs. 4 and 8, and in this Fig. 11, the effects of Figs. 4 and 8 can be obtained simultaneously. Therefore, according to FIG. 11, the black level of the video signal can be taken to the cut-off point P of the cathode ray tube and the back level of this video signal to the point R, regardless of which video signal is transferred. That is, in FIG. 11, as shown in FIG. 5A, the input video signal has the compression effect of the video signal as shown in FIG. In addition, as shown in FIG. 5, when the input signal corresponds to a part of the range of P to R points, the video signal is enlarged to be in the P to R point range as shown in FIG. Have

The autofestal level adjustment circuit according to the present invention operates as follows.

First, the circuit 30 of FIG. 8 detects the darkest part D of the video signal interval as shown in FIG. In this case, the darkest part D is detected only when its level is lower than any graybell L ₁ , and as shown in Fig. 12 Y, the darkest part D is the level. Note that when higher than (L ₁ ), the darkest part D is not detected.

Such operation FIG. 9 A to 9 degrees C and 12 will be described in relation to help, which gray level (L ₁₎ is a ninth also input video signal (1a having a yeokbeul ranking signal, as indicated by a broken line in A It is obtained by adding).

Finally, the input signal shown in FIG. 12 X is converted into a waveform in which the darkest part D is coincident with the pedestal level as shown in FIG. Thereafter, the pedestal level can be brought to a black level or a cut off level by the circuits 34, 35, 36, and 37 as shown in FIGS. 8, 10, and 11. Because the adjustment is made, when the darkest part D is lower than any gray level L ₁ , this darkest part D is made to coincide with the black level.

This auto pedestal level adjustment circuit is more effective when used in combination with the back peak level adjustment circuit described in connection with FIGS. 4 and 6. The reason is that the entire dynamic range of the cathode ray tube (CRT) is effectively used. It is also more effective when the ABL circuits are used in combination as described in FIGS. 10 and 11.

In addition, the present invention is not limited to the above-described embodiment, of course, it is possible to take various other configurations without departing from the gist of the present invention.

Claims (1)

Hog level detecting means (30a, 30c, 30d) for detecting the darkest level lower than any gray level among the intervals of the video signal, and the black level detecting means (30a) for setting the darkest level equal to the black level. Means (30g, 30h, 34, 35, 36, 37) for responding to 30c, 30d, to supply an image signal supplied to the cathode ray tube 13 having a dynamic range between the cutoff level and the separation level. An automatic brightness adjusting device for a television receiver, characterized in that for reproduction.

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