JPH01309593A - Video signal circuit - Google Patents

Abstract

PURPOSE:To prevent an operation to a signal having high color saturation in a low luminance level and to improve a temperature characteristic by synthesizing a luminance signal from R, G and B signals and comparing the level of the luminance signal with a set level in a complementary circuit. CONSTITUTION:The luminance signal is synthesized from the R signal, the G signal, and the B signal at the intersection of a resistance 21 and respective resistances corresponding to the R, G and B signals, namely, a resistance 36, a resistance 37, and a resistance 38. This luminance signal is connected to the bases of transistors 22-24 and compared with voltage set by base voltage C of a transistor 25, and the transistors 22-24 are simultaneously made into a conductive state for the level of the luminance signal over the voltage through resistances 26-28 and operated in respective directions to darken R, G and B signal levels for the signal passing sides of resistances 1-3. Thus, since the luminance signal can be compared with the set voltage for which temperature compensation is obtained, the temperature characteristic can be improved, the circuit is never operated by the signal having the high color saturation in the low luminance level, and further, the dislocation of the operating points of the three colors due to a D.C. offset can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal circuit for a television receiver, and particularly to a white compression circuit used therein.

[Conventional technology]

Recent television receivers are required to have high brightness, and the driving level of the video signal to the cathode ray tube is increasing.

However, when the performance of the cathode ray tube exceeds the underground brightness level, out-of-focus occurs, which is a major hindrance to achieving higher brightness. In order to improve this, signal compression is effective for parts brighter than the medium brightness video signal.

FIG. 5 is a diagram showing a video signal circuit having a conventional white signal compression circuit. In this diagram, 1°2.3 is R,G
, a resistor through which the B signal passes, and 4,536 are R, G, and B output transistors, whose collectors are connected to the cathode ray tube 20.
connected to the cathode of 7, 8.9 are load resistances of the output transistors 4, 5.6 connected to the power supply A, respectively. Also, 14, 15.16 are resistances, 17, 1
8.19 is a diode, and 10 is a Zener diode that determines the set voltage value.

Next, the operation will be explained. The R, G, and B signals pass through resistors 1 and 2.3, which are the respective color amplification circuits, and are inputted from the bases of transistors 4 and 5.6, and their collectors receive an inverted amplified output, and the cathode of the cathode ray tube 20 is input. to drive. On the other hand, on the signal passing side of the resistor 1°2.3, the Zener voltage of the Zener diode 10 and the diode 17.1
There is a set voltage formed by the forward voltage drop of 8.19, and a signal voltage higher than this set voltage is applied to the resistors 14, 15 .
When applied to the intersection of 16 and resistors 1 and 2.3,
A signal current is shunted to resistors 14, 15, and 16. As a result, as shown in FIG. 6, the white signal portion of the R, G, and B signals whose voltage is higher than the set voltage is compressed.

Furthermore, recent television receivers are required to have high image quality as well as high brightness, and the level of contour correction of video signals is also increasing. The focus blur in high-brightness areas as mentioned above is
This is a major hindrance to achieving higher image quality. 7th
The figure shows the signal state near the contour when a high brightness signal higher than the set level is clipped at the set level by using a circuit like the one shown in Figure 5 above to improve this problem, and the broken line is Indicates a clipped state. In this way, since the high, middle, and low frequency ranges are clipped to a constant level, the white level of the contour part is compressed too much, which affects the image quality.

[Problem to be solved by the invention]

Since the conventional white signal compression circuit is configured as described above, it can operate even when the luminance signal level is low or at a signal level with high color saturation, and when there is a DC offset in the R, G, and B signals, The operating points of the three colors are shifted and R, G, and B do not operate at the same time, which adversely affects color reproduction performance. Further, there were other problems such as the Zener diode that determines the set level and the temperature characteristics of the diode cannot be compensated for, and the contour correction section, which has the most adverse effect on image quality, cannot be selectively compressed.

This invention was made to solve the above-mentioned problems.The operating point of white compression is determined based on the luminance signal level, and the three colors are simultaneously processed without being affected by the DC offset of the R, G, and B signals. To obtain a video signal circuit having a white signal compression circuit capable of starting a compression operation, compensating for an operating point shift due to temperature, and selectively increasing a compression rate in a high frequency region which is a contour correction section. With the goal.

[Means to solve the problem]

The video signal circuit according to the present invention synthesizes a luminance signal using R, G, and B signals, and compares the luminance signal with a set voltage using a comparator circuit consisting of a complementary circuit. , RlG, and B signals are each controlled in a current-driven manner to perform white compression operation.

Furthermore, an impedance element for determining a high frequency compression amplification factor is connected to the transistor that performs the above control.

[Effect]

In this invention, a comparison circuit between a luminance signal synthesized by R, G, and B signals and a set voltage is configured by a complementary circuit, and compression of the R, G, and B signals is inserted into each signal path. By connecting an independent current drive circuit to each resistor and controlling the amount of current drive, operation for signals with high color saturation at low brightness levels is prevented, and three-color operation due to DC offset is prevented. Misalignment of points is also prevented.

Furthermore, by connecting an impedance element for determining the high frequency compression amplification factor to the transistor that performs the above control, it becomes possible to selectively compress the high frequency region to a greater extent than the middle and low frequency regions.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 1, 1.2.3 is a resistor through which the R, G, and B signals pass, and 4.5.6 is an R, G, and B output transistor, the collector of which is connected to the cathode of the cathode ray tube 20. , 7.8.9 are load resistances of the output transistors 4.5.6 connected to the power supply A, and these constitute a primary color signal amplification circuit. 36, 37 and 38, 21 are resistors, which combine the luminance signals. Transistors 22, 23, and 24 constitute a complementary circuit with the transistor 25. 26, 27, and 28 are resistors that determine the white compression amplification factor, and 29 is a resistor that determines the operating current of the transistor 25. Further, B is its power supply, and C is a set voltage that determines the white compression operation start level.

The operation will be explained below. The R, G, and B signals pass through resistors 1 and 2.3, respectively, and output transistors 4 and 5.6.
Enter the base of. The inverted and amplified signal drives the cathode of the cathode ray tube 20 from the collectors of the transistors 4, 5, and 6. In order to obtain a luminance signal in this circuit, a resistor of 36 degrees is used for the R signal, and a resistor of 37 degrees is used for the G signal. Resistor 3 from B signal
8, the luminance signal is synthesized at the intersection with the resistor 21. This brightness signal is connected to the bases of transistors 22, 23, 24 and compared with the voltage set by the base voltage C of transistor 25, and for brightness signal levels exceeding this voltage, transistors 22, 23, 24 are resisted. 26.
27 and 28, and operate in the direction of darkening the R, G, and B signal levels on the signal passing sides of resistors 1 and 2.3, respectively. As a result, when the luminance signal level exceeds the set voltage, the signal after passing through the resistors 1 and 2.3 is compressed as shown in FIG. In this Figure 2, a
b is the case where the composite luminance signal is below the voltage C, and b is the case where the composite luminance signal exceeds the voltage C.

Such circuits can compare the luminance signal with a temperature-compensated set voltage, which improves their temperature response, and they do not operate with signals with high color saturation at low luminance levels as in the past, and they also use DC There is also no shift in the operating points of the three colors due to offset.

In the above embodiment, the set voltage C is set by the transistor 25.
Although it is said that there is one by one, R, G.

Three transistors may be used for the three B colors for comparison.

In addition, in the above embodiment, a case has been described in which the three colors R, G, and B are compressed at the same amplification factor, but in order to change the color tone during high-brightness signals, a circuit configuration that does not compress only the - color may be used. It is also possible to have a circuit configuration in which the values of the resistors 26, 27, and 28 are independently set for the three colors R, G, and B to change the compression ratio.

FIG. 3 is a diagram showing a video signal circuit according to another embodiment of the invention. In this figure, 33°, 34.35 is a capacitor, and 30.31.32 is a resistor, which determines the high frequency compression amplification factor.

The operation of this circuit is almost the same as the circuit according to the above embodiment, but when operating in the direction of darkening the R, G, and B signal levels, the control amplification factor of the entire frequency band depends on the value of the resistors 26, 27, and 28. However, the control amplification factor in the high frequency range can be set by capacitors 33, 34.35 and resistors 30, 31.32. As a result, when the luminance signal level exceeds the set voltage, the white outline of the signal after passing through resistors 1, 2, and 3 as shown in Figure 4 is in the middle and low frequency range, as shown by the broken line. It is more compressed than before. Such a selection operation can prevent the conventional overcompression of the white level of the outline portion, and improve the image quality.

In addition, in the above embodiment, the contour part of the video signal is RoG, B
It is assumed that the compression is balanced, but in order to change the color tone of the outline, capacitors 33, 34, 35,
The values of the resistors 30, 31, and 32 may be set differently for each of R, G, and B.

Furthermore, although the resistors 30, 31, and 32 are connected to ground, they may also be connected to the emitter of the transistor 25.

〔Effect of the invention〕

As described above, according to the video signal circuit according to the present invention,
Since the luminance signal is synthesized from the R, G, and B signals and compared with the set level using a complementary circuit, it is possible to prevent operation with signals with high color saturation at low luminance levels, and compression control is performed using current Since it is a drive type, it is not affected by the DC offset of the R, G, and B signals, has good balance, can simultaneously compress the R, G, and B signals with high precision, and has good temperature characteristics.

Furthermore, since an impedance element for determining the high frequency compression amplification factor is connected to the transistor that performs the above control, the compression ratio for the high frequency region and other frequencies can be freely set, which has the effect of improving image quality. be.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing a video signal circuit according to an embodiment of the present invention, FIG. 2 is a diagram for explaining its operation, and FIG.
4 is a circuit diagram showing a video signal circuit according to another embodiment of the present invention, FIG. 4 is a diagram for explaining its operation, FIG. 5 is a circuit diagram showing a conventional video signal circuit, and FIG. Figure, 7th
Each figure is a diagram for explaining the operation. 1 to 3, 26 to 32 are resistors, 22 is a first transistor, 23 is a second transistor, 24 is a third transistor, 25 is a fourth transistor, 33, 34 .
35 is a capacitor, B is a power supply, and C is a set voltage. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In the video signal circuit of a primary color drive television receiver, there is a circuit that synthesizes a luminance signal from the R, G, and B signal outputs, and each collector has a resistor for each of the R, G, and B signals. first, second, and third transistors whose bases are connected to the luminance signal, and whose emitters are connected to the emitters of the first, second, and third transistors through resistors, respectively. and a fourth transistor connected to a circuit through which an operating current flows, whose collector is connected to a power supply, and whose base is applied with a signal suppression level setting voltage. . (2) In the video signal circuit of a primary color drive type television receiver, there is a circuit that synthesizes a luminance signal from the R, G, and B signal outputs, and each collector has a resistor for the R, G, and B signals, respectively. the base of each of which is connected to the luminance signal, and the emitter of each of which is connected to an impedance element for determining a high frequency compression amplification factor.
, a third transistor, whose emitter is connected to the emitters of the first, second, and third transistors via resistors, respectively, and is connected to a circuit that flows an operating current, and whose collector is connected to a power supply, A video signal circuit comprising: a fourth transistor to which a signal suppression level setting voltage is applied to the base thereof.