JPH0294791A - Video blanking circuit - Google Patents

Abstract

PURPOSE:To prevent a state with unstable white balance from being displayed by applying blanking to a video signal for a prescribed time after application of power and releasing the blanking for a period including a reference pulse applied to the cathode of a cathode ray tube. CONSTITUTION:A white balance control circuit 2 increases a DC potential of R.G.B video signal to increase the amplitude of the signal for a period till the heater is warmed sufficiently after the moment of application of power. A timer circuit 8 outputs a signal to operate a blanking circuit 7 for a prescribed time from the moment of application of power and the blanking circuit 7 cuts off a video amplifier circuit 3. Moreover, a pulse generating circuit 9 outputs a signal so that the blanking circuit 7 stops the blanking for a period including the reference pulse inserted to the R.G.B video signal. Thus, the automatic white balance adjustment is continued till the heater is sufficiently warmed from the moment of application of power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television receiver having an automatic white balance adjustment function and a video blanking circuit in a display.

[Conventional technology]

Conventionally, in television receivers and displays that have an automatic white balance adjustment function, when the receiver is turned off and then turned on, sufficient beam current does not flow until the cathode ray tube heater warms up. Since the balance adjustment circuit has already started its operation, it works to lower the DC potential of the cathode waveform and increase the voltage amplitude so as to increase the beam current. Then, as the heater gradually warms up and the beam current gradually begins to flow, the DC potential of the cathode waveform gradually increases and the voltage amplitude also decreases, but since sufficient beam current still does not flow, the video output circuit is amplified. Screen saturation appears due to the collector voltage of the transistor being too low. Furthermore, when the heater heats up sufficiently, a sufficient beam current flows, which increases the collector voltage of the transistor and eliminates screen saturation. That is, in the television receiver having the above-mentioned automatic white balance adjustment function, there is a problem in that the screen becomes saturated for a certain period of time starting from the moment the power is turned on, making it unsightly. Japanese Patent Laid-Open No. 55-67286 solves the above problem by cutting off the automatic white balance adjustment loop for a certain period of time starting from the moment the power is turned on.

[Problem to be solved by the invention]

The above conventional technology stops the automatic white balance adjustment operation for a certain period of time from the moment the television receiver is turned on, and when the cathode ray tube heater is sufficiently warmed up, the automatic white balance: J:I adjustment operation is performed. Start. Automatic white balance tone II inserts a reference pulse into the RGB signal,
The beam currents for RGB are controlled to be constant values, but since the convergence times for RGB do not necessarily match,
From the time the automatic white balance adjustment operation starts until it completes,
A problem arose in that an unstable white balance appeared on the screen.

An object of the present invention is to prevent a state in which the white balance is not constant from appearing on the screen.

[Means to solve the problem]

The above purpose is to provide a timer circuit that determines whether a certain period of time has elapsed from the moment the power is turned on, a blanking circuit that blanks the video signal using the output signal of the timer circuit, and a blanking circuit that blanks the video signal after the vertical blanking period. This is achieved by providing a circuit that stops blanking the video signal during a period that includes the inserted reference pulse for automatic white balance adjustment.

In addition, the control circuit that performs automatic white balance adjustment includes controllers 1 to 1.
Russ! The object is achieved by controlling the contrast 1- and the black level using the output signal of the timer circuit if the system has a control circuit (adjustment circuit) for the contrast 1- and the black level.

[Effect]

From the moment the power is turned on until the heater is sufficiently heated, automatic white balance adjustment operates to lower the DC potential of the cathode waveform and increase the voltage amplitude. Since ranking is applied, screen saturation does not appear on the screen. In addition, in order to stop blanking the video signal during the period including the automatic white balance adjustment (1) γ base t(]! pulse inserted outside the screen after the vertical retrace period, the power is turned on. Automatic mortar balance adjustment can be continued from moment to moment until the heater is sufficiently heated.

After canceling blanking, changes in white balance are no longer cursed on the screen.

In addition, if the control circuit that performs automatic white balance adjustment has a contrast 1 and black level control circuit (adjustment circuit), the output signal of the timer circuit can be used to minimize the contrast and black level. Screen saturation and white balance fluctuations can be prevented from being cursed on the screen.

〔Example〕

Hereinafter, five embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of a video blanking circuit according to the present invention. In the figure, 2 is a control circuit that performs automatic mill balance adjustment, 3 is a video amplification circuit that amplifies the video signal, and 4 to 6 are beam current detection circuits that detect beam current and convert it to voltage.6 Control circuit 2 Now, a reference pulse is inserted into the R-G-H video signal, and the video I! ! JllQ]
Output to circuit 3.

The video signal is amplified by the video amplification circuit 3, passes through the beam current detection circuits 4 to 6, and is input to the cup 1 of the cathode ray tube 1. At this time, the beam current flowing from the cathode is converted into a voltage by beam current detection circuits 4 to 6 and input to the control circuit 2. The control circuit 2 controls the DC potential and signal amplitude of the R-G/B video signals so that the detected voltage becomes a constant value, and adjusts the white balance to: A! ! do. During the period from the moment the power is turned on until the heater is sufficiently heated, the beam 7B current does not flow sufficiently, so the control circuit 2
- Increase the DC potential of the H video signal and increase the signal amplitude. At this time, the video amplification circuit 3 is in a saturated state. Therefore, the timer circuit 8 outputs a signal to operate the blanking circuit 7 for a certain period of time starting from the moment the power is turned on, and the blanking circuit 7 operates so that the video amplification circuit 3 is in a cut-off state. to avoid saturation. Next, while the blanking circuit 7 is operating, the video amplifier circuit 3 is in a cutoff state, so the reference pulse inserted into the R-G/B video signal is not input to the cathode ray tube cathode, and the automatic white balance adjustment operation is also not performed. It becomes stopped.

Therefore, a pulse generation circuit 9 is provided that generates a signal to stop the blanking time and %57 during the period including the reference pulse inserted into the R-G-H video signal, so that the heater is fully activated from the moment the power is turned on. Allow automatic white balance adjustment operation to continue until the temperature is warmed up.

FIGS. 2 and 3 are block diagrams showing one embodiment of the present invention. In FIG. 2, the timer circuit 8 outputs a signal rHighJ for a certain period of time from the moment the power is turned on, and the transistor 13 is turned on. however,
During the period including the reference pulse for automatic white balance adjustment inserted into the video signal, the period including the reference pulse for automatic white balance adjustment is
h Outputs the J signal and turns transistor 16 “ON”
state, and the transistor 13 is brought into the rOFFJ state. When the transistor 13 is in the roNJ state, the transistors 11 and 21 are cut off, and the voltage at the cathode is increased to cut off the cathode ray tube.

In FIG. 3, by raising the potential of the base of transistor 14, transistors 11 and 12 are placed in a cut-off state.

FIG. 4 shows a specific example of the timer circuit 8.

In the figure, an appropriate power supply voltage is supplied to a terminal 71 from the power supply circuit of the television receiver. Therefore, no charge is accumulated in the capacitor 61 in the state of the power supply "l, lll". When the power is turned on, current is supplied to the capacitor 61 through the resistor 27, charge is accumulated, and the base voltage of the transistor 17 gradually increases. 1-The transistor 17 is in the rONJ state until the base voltage reaches the voltage (VCC-VBE) obtained by subtracting the base-emitter voltage from the electric g voltage, and the output terminal 72 is rHigh.
Outputs a voltage of hJ. By appropriately selecting the values of capacitor 61 and resistor 27, a desired timer time can be obtained.

Other possible ways to use the timer include counting the number of horizontal or vertical pulses or the frequency of the power supply.

FIG. 5 shows a specific example of the pulse generation circuit 9.

The vertical blanking pulse is integrated using the resistor 30 and capacitor 62 shown in FIG. 5 to obtain the waveform shown in FIG. 6(d). This waveform is fed through emitter follower 18 and resistor 32 to the base of transistor 16, 1-transistor 1
6 performs the 0N10FF operation at a time delayed from the vertical blanking pulse as shown in FIG. 6(e). The reference pulse for automatic white balance adjustment is inserted two horizontal periods after the vertical blanking pulse, as shown in FIG. 6 (α), so that the rONJ period of the transistor 16 includes the reference pulse. Then, the values of resistor 30 and capacitor 62 are selected. When the transistor 16 becomes roNJ, the output terminal 73 becomes rLOWJ, and blanking stops.

Another possible method is to count horizontal pulses and generate pulses synchronized with reference pulses for automatic white balance and g-alignment.

As a method of blanking the video signal, if the control circuit 2 for automatic white balance adjustment shown in Fig. 1 has a contrast and black level control circuit (circuit for !1m section), the contrast and black level minimize the level,
It is possible to obtain the same effect as applying blanking to a video signal.

〔Effect of the invention〕

According to the present invention, there is an effect that screen saturation and fluctuations in white balance that occur from the moment the power is turned on until the heater is sufficiently heated do not appear on the screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIGS. 2 and 3 are block diagrams showing an embodiment of the invention, and FIG. 4 is a circuit diagram showing a specific example of a timer circuit. , FIG. 5 is a circuit diagram showing a specific example of the pulse generation circuit, and FIG. 6 is a waveform diagram showing a timing chart of the pulse generation circuit. DESCRIPTION OF SYMBOLS 1... Braun tube, 2... Control circuit for automatic white balance adjustment, 3... Video amplification circuit, 4-6... Beam current detection circuit, 7... Blanking circuit, 8... Timer circuit , 9...Pulse generation circuit, 11-18...Transistor, 21-32...Resistor, 41-42...
Voltage source, 51... Diode, 61-62... Capacitor, 71... Power supply voltage supply terminal. 72-73... Output terminals. 3 countries

Claims (1)

[Claims] 1. In a video display device having an automatic white balance adjustment function that applies a reference pulse to the cathode ray tube cathode and keeps the beam current flowing during the pulse period constant to obtain white balance, from the moment the power is turned on. A video blanking circuit that applies blanking to a video signal for a certain period of time, and cancels the blanking during a period that includes a reference pulse applied to a cathode of a cathode ray tube. 2. The blanking circuit according to claim 1, wherein the blanking circuit is controlled so that the contrast and black level are minimized.