JPH05199536A - Video mute circuit - Google Patents

Abstract

PURPOSE:To provide a video mute circuit for automatically changing the mute time of video signals corresponding to the heated state of the heater of a cathode ray tube for a mute voltage to be supplied to the video mute circuit concerning the video mute circuit for preventing any abnormal white balance phenomenon when turning on the power source of an automatic white balance circuit to stably keep white balance. CONSTITUTION:A video mute circuit 6a can mute video signals except for a reference signal to control a beam current by amplifying the output signal of a circuit 4 to detect the beam current of a color cathode ray tube 5 and controlling the mute voltage supplied from a power source by delayed and DC converted signals, and there is an effect to automatically change the mute time corresponding to time until the beam current flows to the cathode ray tube 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance technique for maintaining a stable white balance of a cathode ray tube for several tens of minutes after the power switch is turned on in a color television receiver, or when used for many years. Although it has been introduced into products, the present invention relates to a video mute circuit technology for solving the problem of this circuit, that is, the phenomenon that the white balance is abnormally collapsed at the moment when the beam current flows into the CRT when the power switch is turned on.

[0002]

2. Description of the Related Art In recent years, color television receivers have been used for various purposes from home use to business use and are required to have high functionality, high performance and high reliability. Under these circumstances, the adoption of an automatic white balance circuit as a white balance stabilization technology for color CRTs has greatly improved the stability after the power switch is turned on and the change in white balance over time. However, against the phenomenon that the white balance that occurs when the power switch is turned on, which is a drawback of this automatic white balance circuit, is abnormally collapsed, the rise of the power supply is used to blank the video signal for a certain period of time and erase the video signal from the CRT. Measures are taken by using circuits.

A conventional video mute circuit will be described below. FIG. 4 shows a video mute circuit in a conventional automatic white balance circuit, and reference numeral 6 shows an output signal waveform thereof. In FIG. 4, reference numeral 1 denotes a video signal processing circuit which receives the composite video signal a (6a) and adjusts the demodulation of the color signal, the saturation of the color and the hue, and the contrast of the luminance signal and the black level. The output signal b (6b) is RG
It is output as a B primary color signal. An automatic white balance circuit 2 outputs a signal c (6c) in which a reference signal for controlling the beam current of the cathode ray tube is fitted immediately after the vertical blanking period. A video amplification output circuit 3 outputs a signal d (6d) obtained by amplifying a video signal to a specified amplitude according to the specifications of the cathode ray tube. Reference numeral 4 is a detection circuit of the beam current flowing through the cathode ray tube, and its output signal e (6
In e), the reference signal for controlling the beam current flowing in the cathode ray tube is converted into a voltage, and only this reference signal is output and fed back to the automatic white balance circuit 2. 5 is a cathode ray tube. A video signal mute voltage generation circuit 6 detects the rising of the power supply 8 with the capacitor 31 and the resistor 21 and detects the video output signal c for a certain time of the rising of the power supply.
Only the video signal excluding the beam current detection reference signal (6c) is muted. Reference numeral 7 is a white balance setting circuit for setting the cutoff voltage and output amplitude of the RGB electrodes of the cathode ray tube, the output of which is supplied to the automatic white balance circuit 2 to adjust the black level and amplitude of the RGB output signal c (6c). And adjust the white balance of low light and high light. Further, the output signal e (6e) of the beam current detection circuit 4 is constantly compared with the output voltage f of the white balance adjustment circuit 7 so that the output signal e (FIG. 3e) of the beam current detection circuit 4 becomes constant. The automatic white balance circuit 2 operates to automatically control the white balance so that the beam current of the reference signal flowing through the cathode ray tube is always constant.

The operation of the video mute circuit 6 of the automatic white balance circuit configured as described above will be described below. FIG. 4 is a diagram for explaining the operation. The Y-axis a is voltage, the X-axis b is time, and the waveform c is mute voltage waveform. First, a capacitor 31 is connected to the power source 8 and is grounded by a resistor 21 through the capacitor 31, and the intersection of the capacitor 31 and the resistor 21 is connected to the mute terminal of the automatic white balance circuit 2. This mute circuit forms a differentiating circuit with the capacitor 31 and the resistor 21, detects the rising of the power supply 8, and supplies the voltage of the waveform chart 4c to the mute terminal. The video output signal is muted up to the point of time chart 4i, which is higher than the mute release voltage chart 4g, but at the point of time chart 4i, the mute voltage becomes the mute release voltage chart 4g and the mute is released and the video signal is output. .. At this time, at the time of FIG. 4i, the beam current starts to flow through the cathode ray tube, and the automatic white balance circuit needs to be operating stably, which requires a sufficient mute time. In such a case, when the CRT is cold enough, the mute time is long, but even when the power is off for a few seconds, the mute time is too long.
There is a drawback that the time until the image signal is output is too late.

[0005]

However, in such a conventional configuration, the mute time cannot be dealt with according to the state of the cathode ray tube, and the mute time is too long even when the power is turned on after the power is turned off for several seconds. However, there is a problem that the output of the video signal is delayed.

The present invention is to solve the above-mentioned problems. When the state of the cathode ray tube is detected and the power is turned on when the cathode ray tube is cold, the mute time is sufficiently long, and when the power is turned on after the power is turned off for several seconds, the mute is performed. It is an object of the present invention to provide a video mute circuit which solves the above problem by detecting that a beam current has flowed in a cathode ray tube such as shortening the time and canceling mute.

[0007]

To achieve this object, a video mute circuit of the present invention includes a reference signal generating circuit for controlling a beam current of a cathode ray tube using a color cathode ray tube and an image signal other than the reference signal. An image mute circuit comprising an automatic white balance circuit having a circuit for muting, a beam current detection circuit for a cathode ray tube, and a circuit for producing a mute voltage of a video signal by a beam current detection output signal.

[0008]

With the above-described structure, the present invention outputs the video signal and the reference signal for controlling the beam current of the cathode ray tube from the automatic white balance circuit after the power is turned on, but the beam current does not flow because the cathode ray tube cools and the beam current does not flow. Does not output a voltage, but a high voltage is output from the mute voltage generation circuit and the video mute circuit operates to output only the beam current control reference signal. When the CRT becomes warm and the beam current flows into the CRT with the beam current control reference signal, a voltage is output from the beam current detection circuit and the voltage stops after a certain time from the mute voltage generation circuit and the video mute circuit stops operating. And output a video signal. In this way, when the beam current does not flow to the cathode ray tube, the image mute circuit operates to stop the image output of the cathode ray tube, and when the beam current starts to flow, the operation of the image mute circuit is stopped after a certain period of time to output the image signal. It is possible to automatically change the mute time according to the state of the cathode-ray tube to prevent abnormal white balance when the power is turned on.
The mute time of the video signal can be automatically changed according to the heating state of the cathode ray tube heater.

[0009]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a video signal processing circuit, 2
Is an automatic white balance circuit, 3 is an image amplification output circuit,
Reference numeral 5 is a cathode ray tube, 6a is a video signal mute voltage generating circuit, and 7 is a white balance setting circuit. These configurations are the same as the conventional circuit example except for the video signal mute voltage generating circuit of 6a, and therefore omitted. The video signal mute voltage generation circuit 6a will be described. 22, 23
Is the base bias resistance of the transistor 51 for dividing the output voltage of the beam current detection circuit, 24 is the collector load resistance,
51 a transistor for switching and amplifying a beam current detection signal, 52 a transistor for impedance conversion of an output signal of the transistor 51, 25 a transistor 52
Is a load blocking resistor, 32 is a DC blocking capacitor for the switching amplified beam current detection output signal, 42 is a diode for clamping the DC blocked beam current detection output signal to ground, and 26 is a leak resistor. Reference numeral 27 is a resistor, and 33 is a capacitor, which is connected to the base of a transistor 53 which performs a switching operation by rectifying the average value of the beam current detection output signal by the resistor 27 and the capacitor 33 into a DC signal. Reference numeral 28 denotes a load resistance of the transistor 53, and the DC-converted beam current detection output signal is connected to the mute circuit of the automatic white balance circuit 2. 8a is a power supply for this circuit.

The operation of the video mute circuit configured as described above will be described with reference to FIG. First, when the power is turned on while the cathode ray tube is cold, a signal is not output to the beam current detection circuit 4 because the beam current does not flow in the cathode ray tube, the transistor 51 is turned off, and the signal is transmitted to the capacitor 32. Without this, the transistor 53 is off. Since the power supply voltage (FIG. 3c) is supplied from the power supply 8a to the video mute circuit of the automatic white balance circuit 2 through the resistor 28, the output signal of the automatic white balance circuit 2 mutes the video signal and only the reference signal for beam current detection is used. Is output. When the heater of the cathode ray tube starts to warm, a current starts to flow in the cathode ray tube by the beam current detection reference signal, and the beam current gradually increases from point j in FIG. 3 and stabilizes (FIG. 3e). When the beam current begins to flow, a voltage signal similar to the reference signal is output from the beam current detection circuit 4, switching amplified by the transistor 51, and clamped to a higher potential than the ground by the capacitor 32 and the diode 42 with reference to the ground. Resistor 27 and capacitor 33
At the same time, the signal is converted into a direct current at the same time, and the signal is delayed, the transistor 53 is turned on at the point of FIG. 3i, the mute signal supplied from the power source through the resistor 28 is rapidly attenuated, and the mute is released at the point of FIG. The video signal is output. When the power of the cathode ray tube heater is turned on, the beam current flows immediately after the power is turned on by the beam current detection reference signal from the point of FIG. 3k, so that the transistor 53 operates at the point of FIG. 3h and the mute occurs at the point of FIG. 3f. Will be canceled.

As described above, according to this embodiment, by providing the mute voltage generating circuit for the video signal by using the output signal of the beam current detecting circuit, the abnormal white balance phenomenon after the power is turned on is prevented and the cathode ray tube The video mute time can be automatically changed according to the heating state of the heater.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1
Is a video signal processing circuit, 2 is an automatic white balance circuit,
3 is a video amplification output circuit, 5 is a cathode ray tube, 6b is a video signal mute voltage generation circuit, and 7 is a white balance setting circuit. These configurations are the same as the conventional circuit example and the functional operation except for the video signal mute voltage generation circuit 6b. Since they are the same, the description thereof will be omitted, and the video signal mute voltage generating circuit 6b will be described. 22 and 23 are base bias resistors of the transistor 51 for dividing the output voltage of the beam current detection circuit, and 24
Is a collector load resistance, 51 is a transistor for switching and amplifying the beam current detection signal, and 52 is a transistor 51.
Transistor for impedance conversion of output signal of 2
Reference numeral 5 is an emitter load resistance of the transistor 52, 32 is a DC blocking capacitor for the switching amplified beam current detection output signal, 42 is a diode for clamping the DC blocked beam current detection output signal to the ground, and 26 is its leakage. It is resistance. Reference numeral 27 is a resistor, and 33 is a capacitor, which is connected to the base of a transistor 53 which performs a switching operation by rectifying the average value of the beam current detection output signal by the resistor 27 and the capacitor 33 into a DC signal.
8b is a power source for this circuit, 31b is a capacitor, 21b is a resistor, and a capacitor 31b and a resistor 21b form a differentiating circuit, the power supply voltage passes through this differentiating circuit, and this output voltage is a mute of the automatic white balance circuit 2 Supplied to the circuit. Further, this differential circuit output signal is connected to the collector of the switching transistor 53, and is blocked by the beam current detection signal supplied from the base.

The operation of the video mute circuit configured as described above will be described with reference to FIG. First, when the power is turned on while the cathode ray tube is cold, a signal is not output to the beam current detection circuit 4 because the beam current does not flow in the cathode ray tube, the transistor 51 is turned off, and the signal is transmitted to the capacitor 32. Without this, the transistor 53 is off. Since the video mute circuit of the automatic white balance circuit 2 is supplied with the mute voltage FIG. 4c from the power supply 8b and the differentiation circuit of the capacitor 31b and the resistor 21b, the output signal of the automatic white balance circuit 2 mutes the video signal and detects the beam current. Output only the reference signal for use. When the heater of the cathode ray tube starts to warm up, the reference signal for beam current detection causes current to flow into the cathode ray tube.
From the point, the beam current gradually increases and stabilizes (FIG. 4e).
When the beam current begins to flow, a voltage signal similar to the reference signal is output from the beam current detection circuit 4 and switching-amplified by the transistor 51, and the capacitor 32 and the diode 4
At 2, it is clamped to a higher potential than earth with respect to earth. At the same time as the DC conversion is performed by the resistor 27 and the capacitor 33, the signal is delayed and the transistor 53 is turned on at the point of FIG. 4i, and the mute voltage supplied from the power source through the differentiating circuit of the capacitor 31b and the resistor 21b is rapidly attenuated and the signal is delayed.
At point g, the mute is released and the video signal is output from the automatic white balance circuit. In addition, when the power is turned on while the heater of the cathode ray tube is warmed up, after the power is turned on, FIG.
Since the beam current flows immediately from the point by the beam current detection reference signal, the transistor 53 operates at the point of FIG. 4h and the mute is released at the point of FIG. 4f. The mute voltage output from the differentiating circuit of the capacitor 21b and the resistor 31b is the capacitor 31 when the transistor 53 operates.
Since b rapidly charges and completes charging, no voltage is generated and the video mute circuit does not operate again unless the power is turned on again.

As described above, according to this embodiment, by providing the differentiating circuit for detecting the rise of the power supply voltage and the mute voltage generating circuit for the video signal using the output signal of the beam current detection circuit, an abnormal condition after the power is turned on is provided. In addition to preventing the white balance phenomenon, the video mute time can be automatically changed according to the warm state of the cathode ray tube heater. Further, once the video mute circuit is released, the mute circuit does not operate unless the power is turned on again, so that the normal operation state can be achieved regardless of the operation state of the mute voltage generation circuit.

In the second embodiment, the capacitor 31b and the resistor 21b are used to detect the rise of the power supply voltage.
However, a mute voltage generating circuit using a microcomputer and a transistor may be used.

[0017]

As is apparent from the above-described embodiments, according to the present invention, an automatic white circuit provided with a reference signal generating circuit for controlling the beam current of the cathode ray tube and a circuit for muting a video signal other than this reference signal. Balance circuit,
By providing a beam current detection circuit for the cathode ray tube and a circuit that creates the mute voltage of the video signal with the beam current detection output signal, an abnormal white balance phenomenon after the power is turned on can be prevented, and according to the heating state of the heater of the cathode ray tube. (EN) It is possible to provide an image mute circuit of an automatic white balance circuit that can automatically change the image mute time and can maintain a stable white balance during image output.

[Brief description of drawings]

FIG. 1 is a block diagram of a video mute circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a video mute circuit according to a second embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the video mute voltage generation circuit in the first embodiment.

FIG. 4 is a waveform diagram for explaining the operation of the video mute voltage generating circuit in the second embodiment.

FIG. 5 is a block diagram of a conventional video mute circuit.

FIG. 6 is a waveform diagram for explaining the operation of the video mute circuit in the conventional example.

FIG. 7 is a waveform diagram for explaining the operation of the video mute voltage generating circuit in the conventional example.

[Explanation of symbols]

 1 Video Signal Processing Circuit 2 Automatic White Balance Circuit 3 Video Amplification Output Circuit 4 Beam Current Detection Circuit 6 Mute Voltage Generation Circuit 7 White Balance Setting Circuit 21-28 Resistor 31-33 Capacitor 42 Diode 51-53 Transistor

Claims (2)

[Claims] 1. A reference signal generation circuit for controlling a beam current of a color cathode ray tube, an automatic white balance circuit having a circuit for muting a video signal other than the reference signal, and a beam current detection circuit for detecting a beam current of the cathode ray tube. And a video mute circuit that removes the video signal depending on the presence or absence of the beam current of the cathode ray tube, which is composed of a circuit that creates a mute voltage for the video signal with the beam current detection output signal. 2. A reference signal generation circuit for controlling a beam current of a color cathode ray tube, an automatic white balance circuit having a circuit for muting a video signal other than the reference signal, and a beam current detection circuit for detecting a beam current of the cathode ray tube. The beam current detection signal of the cathode ray tube is composed of a mute voltage generation circuit that generates a voltage for removing the video signal for a certain time when the power is turned on, and a circuit that removes the mute voltage according to the beam current detection output signal. A video mute circuit that cancels the removal of the video signal.