JPS597273B2 - Color picture tube cut-off adjustment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cutoff adjustment circuit for a color picture tube.

``In general, color television receivers require adjustment to align the cutoff points of the Kass 7 picture tube (7) and each electron gun, that is, cutoff adjustment.

This adjustment is to simultaneously cut off the video signal and vertical deflection so that horizontal bright lines of red R, green IG, and blue B are slightly visible on the surface of the color picture tube. Therefore, auxiliary means are required to perform the cutoff adjustment. 1st
The figure shows a picture tube circuit of a color television receiver provided with a conventional general cutoff adjustment circuit.

1 is an input terminal to which a detected video signal is applied; 2
3 is a video amplification circuit, 3 is a collector-grounded video amplification transistor, 100, 200, and 300 are video output circuits, 50 is a color picture tube, and terminals 10, 20, and 30 are color signal processing circuits (
(not shown) and demodulated each color difference signal G-
Input terminal to which Y, R--Y, B-Y are applied, terminal 11
, 21, and 31 are output terminals for the primary color signals G, R, and B, respectively; 400 is a circuit for adjusting the voltage applied to the G2 electrode (screen grid) of the color picture tube 50; and 51 is a signal obtained from a synchronous separation circuit (not shown). an input terminal for applying a vertical synchronization signal based on the received synchronization signal; 52 is a vertical oscillation circuit;
3 is a circuit that generates, amplifies and shapes a sawtooth wave voltage from the oscillated signal; 54 is a drive circuit that excites the output circuit; 60
SRPP (ShuntRe
A vertical output circuit consisting of a ?gulatedPushPull) circuit? 0 is a deflection coil.

Further, reference numeral 4 denotes an adjustment service switch which performs normal operation when it is on the ON side, and disables the vertical oscillation circuit 52 and cuts off the supply of video signals to each video output circuit when it is on the OFF side. The resistor 40 is a screen grid (
G2) A variable resistor provided within the voltage adjustment circuit 400. The variable resistor 12 provided in the video output circuit 100 is for matching the pedestal level of green G of the primary color signal with the cutoff level of the electron gun.
The variable resistor 22 provided in the video output circuit 2Q0 and the variable resistor 32 provided in the video output circuit 300 are also used in order to match the pedestal level of red 1R and blue B with the cutoff level of the electron gun. belongs to. The above circuit configuration is well known and its operation will be briefly described. The image signal applied to the terminal 1 is sent to the video amplification circuit 2, where it is amplified and processed by pedestal clamping, etc., and then impedance-converted by the common collector video amplification transistor 3, passed through the service switch 4, and sent to each video output circuit. 100, 200, 300 are supplied. Then, each color difference signal G-Y, R-Y applied to terminals 10, 20, 30
, B-Y and the video signal (luminance signal Y) are mixed (matrixed) to obtain primary color signals G, R, and B at output terminals 11, 21, and 31, respectively.

Each of the primary color signals energizes a respective cathode KG, KR, KB of the picture tube 50. To perform cutoff adjustment, first, receive a black and white broadcast with as wide a contrast range as possible.

And screen grid (G2) voltage adjustment circuit 40
0 variable resistor 40 is squeezed to darken the screen. Next, the service switch 4 is turned to the 0FF side to stop vertical deflection. At this time, since the video signal is cut off, a DC voltage is applied to each cathode KG, KR, and KB. Here, when the variable resistors 12, 22, 32 and the variable resistor 40 are adjusted, horizontal bright lines of the three colors G, R, and B appear at the center of the picture tube surface. Therefore, each variable resistor 12, 22,
32 independently and fixed at the point where the horizontal bright line of each color begins to be faintly visible. In this way, the cutoff points of each electron gun of the color picture tube can be adjusted to be the same, that is, the cutoff adjustment can be performed. Such a conventional cutoff adjustment method requires two service switches to cut off the video signal and stop the vertical deflection at the same time, which also poses a problem in terms of cost. Furthermore, since the video amplification circuit is completely disconnected during adjustment, there are drawbacks such as the cut-off point being shifted from that during actual operation, which also causes the white balance to collapse in dark images. Hence,
The main object of the present invention is to provide a cutoff adjustment circuit that can solve the above problems and drawbacks at the same time.

To summarize, the present invention provides a control terminal of a gain control circuit whose gain is controlled by a DC control voltage in a video amplifier circuit, and a vertical deflection circuit that has a voltage change lower than the DC control voltage and in a positive direction. Therefore, cutoff adjustment is performed by providing an appropriate bias terminal that stops the vertical deflection and shorting the control terminal and the bias terminal.

The above objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings. FIG. 2 is a picture tube circuit diagram showing an embodiment of the present invention. The difference from FIG. 1 is that the service switch 4 shown in FIG. This is because a terminal T2 is provided which is drawn out from the DC control section of the gain control circuit.
Note that FIG. 2 shows in detail the video amplification circuit 2, vertical 1 drive circuit 54, and vertical output circuit 600 of FIG. 1. In the video amplifier circuit 2, transistors Trl and Tr
A gain control circuit is constituted by a differential amplifier consisting of 2 and Tr3. That is, if the DC voltage at the connection point p is controlled by adjusting the variable resistor RB, the transistors Tr2 and Tr
The current ratio of 3 changes and the gain changes. Now, if the variable resistor RB is changed to the +B1 power supply side and the DC control voltage at the connection point p is increased, the gain of the output signal output from the collector of the transistor Tr2 increases. Conversely, when the DC control voltage at the connection point p is lowered, the gain decreases. 3A and 3B are operation waveform diagrams of various parts of the circuit shown in FIG. 2.

Figure 3A shows the actual operation, a is a sawtooth voltage waveform applied to the base of the vertical 1 driving transistor Tr4, B, c
are transistors Tr6 constituting the SRPP circuit, respectively.
This is the collector voltage waveform of Tr6l. A in Figure 3B
, b, and c are voltage waveforms seen at portions corresponding to A, b, and c in FIG. 3A during cut-off adjustment, that is, when terminals T1 and T2 are short-circuited. To describe it specifically in accordance with FIG. 2, firstly, in the first half of the vertical scanning period, the transistor T
r6l is set to 0FF, and transistor Tr6O is set to +B3
The base voltage provided by the power supply and resistors R1, R2, and R3 makes it 0N.

In the second half of the vertical scanning period, the transistor Tr6l becomes 0N, and the base voltage of the transistor Tr6O decreases due to the voltage drop across the resistor R1, and this transistor Tr6O becomes 0FF.
becomes. During this time, the output current flows through the deflection coil 70 through the DC blocking capacitor 62. Here, terminal T1 and terminal T2 are short-circuited for cutoff adjustment.

Accordingly, the connection point p of the gain control circuit section in the video amplifier circuit 2
and the base of the vertical drive transistor Tr4 are short-circuited. In this way, the vertical drive transistor Tr4 reaches saturation and its base is grounded via the emitter resistor R4. This emitter resistor R4 is selected to be sufficiently small compared to the impedance when viewing the video amplifier circuit 2 from the terminal T2, so the voltage at the connection point p is almost at the ground level, and the transistors forming the differential amplifier of the video amplifier circuit 2 Tr2 becomes 0FF, and the gain of the video signal becomes O. In this way, substantially the video output circuit 1
Video signals to 00, 200, and 300 are blocked. Next, in the vertical deflection circuit section, the vertical drive transistor T
Since the base waveform of r4 becomes a DC level as shown in Figure 3B a, the transistor Tr6l is also saturated and its collector waveform is almost at O level as shown in Figure 3B. If the collector waveform of is at a constant level as shown in FIG. 3c, no deflection current flows through the deflection coil.

In this way, vertical scanning is essentially stopped.
As described above, according to the present invention, there is no need for a service switch that was conventionally provided to cut off the video signal and stop vertical oscillation, and the video amplification circuit remains connected to the video output circuit, so the cut-off circuit is not required. This also eliminates the drawback that the cutoff point of the electron gun differs during adjustment and during actual operation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a picture tube provided with a conventional cutoff adjustment means. FIG. 2 is a circuit diagram of a picture tube provided with cut-off adjusting means according to an embodiment of the present invention. FIG. 3A is a voltage waveform diagram of various parts of the circuit of FIG. 2 during actual operation. FIG. 3B is a diagram of voltage waveforms at various parts of the circuit shown in FIG. 2, which occur during cut-off adjustment. In the figure, the same reference numerals indicate the same or corresponding parts, 2 is a video amplification circuit, RB is a variable resistor for gain control, 100, 200, 300 are video output circuits, 12,
22 and 32 are cut-off adjustment variable resistors, 400 is a screen voltage adjustment circuit, 40 is a screen voltage adjustment variable resistor, 54 is a vertical drive circuit, Tr4 is a vertical drive transistor, 600 is a vertical output circuit, 70 is a deflection coil, T
1 and T2 indicate terminals.

Claims (1)

[Claims] 1. A television receiver having a video amplifier circuit including a gain control circuit whose gain is controlled by a DC control voltage, and a vertical deflection circuit including a vertical drive transistor and an SRPP circuit driven by the vertical drive transistor, a first connected to the base of the vertical drive transistor;
a second terminal connected to an output point of the DC control voltage applied to the gain control circuit, a means for short-circuiting the first terminal and the second terminal, the second terminal The voltage is selected to be higher than the first terminal voltage, and the emitter resistance of the vertical drive transistor is selected to be sufficiently lower than the impedance when the video amplification circuit is viewed from the second terminal. Picture tube cutoff adjustment circuit.