JPS5952873B2 - Video amplification circuit for color television receivers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video amplification circuit for a color television receiver, and particularly to a circuit for adjusting the cutoff voltage of a cathode ray tube.

As shown in FIG. 1, the primary color drive system of conventional color television receivers is comprised of a circuit that matrixes luminance signals and color difference signals at an output stage.

Therefore, when adjusting the cutoff of the cathode ray tube, switch SW
I was opened to stop the supply of the luminance signal, and at the same time, the vertical deflection was stopped to output one horizontal raster, and the cutoff adjustment volumes R10 to R12 and the screen volume (not shown) of the CRT were adjusted. At this time, the color difference output of the color difference signal processing circuit 1 is a fixed potential of DC, so if the cutoff adjustment volumes R10 to R12 are set to a certain fixed position, the collector voltage becomes a fixed voltage, and it is cut off. If you set it to voltage, you can easily adjust the screen volume by looking at the lighting effect of the raster. Here, R1 to R3 are drive adjustment volumes, but since they are well known, their explanation will be omitted. Recently, color television receivers have been made smaller and more sophisticated using IC technology, and color difference signal and luminance signal processing circuits 1,
2 is integrated into an IC and is designed to provide primary color output.

Therefore, the primary color output amplification circuit is composed of a simple amplifier. At this time, there were many problems in adjusting the cutoff of the primary color output amplifier circuit, such as eliminating the luminance signal and fixing the collector voltage, and there was no easy method. The present invention provides a video amplification circuit that solves the above problems, and one embodiment thereof will be described below with reference to the drawings. In FIG. 2, under normal conditions, switch 53 is ON and switch 52 is OFF.
FF and switch 51 are ON.

The composite video signal is transmitted through resistors R36 and R of the luminance signal processing circuit 11.
3l biased, transistor Q15, resistor R28
, R29 and appears at the emitter of transistor Q14. Since the color difference signals are applied from the color difference signal processing circuit 12 to the bases of the transistors Q7 to Q9, the primary color signals appear at the bases of the transistors Q4 to Q6, and are transmitted to the transistors Q1 to Q1 of the primary color output amplifier circuit 13 by emitter followers.
Q3 and resistors R1 to R15, and each collector output is applied to the cathode terminals 14, 15, and 16 of the three primary colors of the cathode ray tube. A blanking pulse is applied from terminal 17 to the bases of transistors Q11 to Q13 for blanking. The resistor R30 can be used in a brightness control polyurethane. When adjusting cutoff, switch S3 is 0FF, switch S2 is 0N, switch S
1 becomes 0FF.

Since the switch S3 is 0FF, the base voltage of the transistor Ql5 becomes O, the collector voltage becomes +B, and no video signal appears. Then, the matrix amplifier of transistors Q7 to Q9 becomes saturated, and the collector voltage becomes a high voltage determined by +B and the values of resistors R19 to R27. This voltage passes through the emitter follower and is applied to the bases of transistors Q1-Q3. Since the switch S1 is 0FF, the cut-off adjusting polyurethane RlO to Rl2 is set as in FIG.
Recut-off adjustment can be made by adjusting . Resistors R4 to R6 are used to set the collectors of transistors Q1 to Q3 to a fixed value, and in the case of Fig. 2, resistor R
It is also possible to replace it with 4. Switch S2 is used to eliminate blanking pulses during cutoff adjustment. Without this switch, transistors Q7 to Q9 would be unsaturated during the blanking pulse period and saturated during other periods, so transistors Q7 to Q9 would be Due to the hole storage effect, a whisker that exceeds the steady voltage is generated,
Makes a cathode ray tube emit light.

However, this is not always necessary depending on the selection of the resistors Rl9 to R27. In this way, first, in order to eliminate the video signal, the bias of the luminance signal processing circuit 11 is maximized or minimized, and the matrix amplifier is saturated at the upper limit of the circuit's dynamic range.

In this way, the video signal disappears and at the same time, the base of the primary color output amplifier circuit] 3 becomes a high DC voltage. Next, the drive adjustment polyurethanes R1 to R3 connected to the emitters of the primary color output amplification circuit 13 are opened to ground.
At this time, the resistors R4-R12 including the cut-off adjusting polyurethane connected between the emitter and the ground are sufficiently higher than the open drive adjusting polyurethane R1-R3, and set the collector voltage to a determined value. This makes it easy to adjust the cutoff. In addition, the part to the left of the dashed-dotted line in the figure is composed of an IC, and the polyurethane R3O
Only the switch S3, the switch S2, and the resistor R32 need to be externally connected. According to the present invention, the output voltage of the color difference signal processing circuit is brought to the upper limit of the dynamic range to eliminate the luminance signal, and Since the switch on the emitter side of the primary color amplification circuit is opened to fix the output voltage of the primary color amplification circuit, the primary color is fixed regardless of the brightness control circuit, contrast control circuit, and image quality control circuit normally included in the brightness signal processing circuit. The output voltage of the amplifier circuit can be fixed.

Furthermore, since the same adjustment method as the conventional method is possible, it is possible to improve the convenience of the user.

[Brief explanation of the drawing]

FIG. 1 is a conventional video amplification circuit diagram, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 11... Luminance signal processing circuit, 12...
Color difference signal processing circuit, 13... Primary color output amplification circuit, R1 to R3... Drive adjustment polyurethane, R
lO~Rl2...Cut-off adjustment polyurethane.

Claims (1)

[Claims] 1. In a color television receiver in which a primary color signal is applied to the base of a primary color signal amplification transistor, the amplified primary color signal is taken out from the collector, and applied to the electrode of a cathode ray tube, three primary color signals are used to extract the amplified primary color output. A cutoff adjustment volume is connected to each emitter of the transistor of the amplifier circuit, and a switch is provided in series between the drive adjustment volume connected to the emitter side and ground, and a primary color signal is supplied to the base of the primary color amplifier circuit. A video amplification circuit for a color television receiver, comprising a circuit that fixes the output voltage of a color difference signal processing circuit to an upper limit value of a dynamic range during cutoff adjustment.