JPH0477082A - Automatic cut-off control circuit - Google Patents

Abstract

PURPOSE:To make a cut-off point stable without deteriorating the frequency characteristic by not providing a cut-off adjustment circuit in a signal path, generating a DC recovery voltage in response to a cathode current detecting voltage and applying it to a signal after DC component cut-off. CONSTITUTION:The cut-off adjustment has been implemented in a conventional circuit such that the output of a sample-and-hold circuit 4 is fed to a Y signal by an adder 3 in a path of the Y signal, but in this configuration, after the output of the sample-and-hold circuit 4 is amplified by an amplifier circuit 10, the signal is fed to a signal component through a capacitor 8 in a DC recovery circuit 9 to apply DC component recovery. That is, the DC component is once cut off in the signal path and the DC recovery level is controlled by the DC recovery circuit 9 as to the cut-off adjustment. Since the signal component is fed directly to a CRT 6 via the capacitor 8, no fluctuation in the operating point of the video amplifier circuit nor fluctuation in the dynamic range takes place and then the frequency characteristic is not deteriorated.

Description

[Detailed Description of the Invention] [Object of the Invention] [Industrial Application Field] The present invention is directed to color cathode ray tube display devices (hereinafter referred to as color CRTs).
The present invention relates to an automatic cutoff control circuit for a display device (referred to as a display device), and particularly to an automatic cutoff control circuit that does not cause deterioration of frequency characteristics even when used in a high-definition color CRT display device.

[Prior Art] Conventionally, in a color CRT display device, R,
It is equipped with a cutoff adjustment circuit to correct variations in the cutoff voltage (cathode voltage at which the cathode current becomes zero) of the G and B three axes and to balance the point when the screen is darkened. Generally, products are shipped after this adjustment.

However, in CRTs, the mechanical gap between the first grid pole G1 and the cathode fluctuates over time, resulting in a problem in that the cut-in and off-points deviate from the factory-adjusted states.

Therefore, conventionally, as a means to improve such a shift in the cutoff point, automatic cutoff 1 as shown in FIG.
A control circuit was used. Although only one axis (R axis) is shown for simplicity, similar control circuits are configured for the B and G axes as well.

In FIG. 2, a luminance signal (referred to as a Y signal) is input to an input terminal 1. This Y signal is the third
As shown in Figure (a), the vertical blanking period (V,
This is a signal in which a reference pulse, which serves as a reference for cutoff adjustment, is inserted into a predetermined horizontal scanning period of BLK. Insertion of the reference pulse into the Y signal is performed by circuit means not shown. The Y signal into which the reference pulse has been inserted is applied to the base of the transistor Q1 in the video output circuit via the cutoff adjustment circuit (comprised of an adder) 3. Further, the RY signal is input to the input terminal 2, and the RY signal is applied to the base of the transistor Q2 of the video output circuit 5. The video output circuit 5 includes a matrix section (two NPN l-transistors Ql, Q2, a resistor R1) that inputs the Y signal and the RY signal and takes out the primary color signal (-] signal).
), an output section (including a PNP transistor Q3, an NPN transistor Q4) that amplifies the -R signal obtained from the collector of the transistor Q2 and supplies it to the R-axis cathode of the CRT6, a cathode current detection resistor R2, and It is composed of a resistor R3, a diode D1, and a DC power supply 1B.

The source current I is passed through a transistor Q3 and is connected to a resistor R2.
It is converted into a voltage V at , and is input to the ~ terminal of the error amplifier 7. A reference voltage E1 is applied to the terminal of the error amplifier 7, and the error amplifier 7 outputs error voltages between Vk and El. This error voltage is supplied to the sample hold circuit 4 and held during the period of the reference pulse, and the cutoff adjustment circuit F! Added to @3. The sample and hold circuit 4 is composed of a switch SW1 and a hold circuit HOL, and the switch SWI is supplied with a keying pulse (see FIG. 3(b)) synchronized with the reference pulse, and is turned on during the period of the reference pulse. The error voltage is bolded.

In the above configuration, when the cathode current I is large and the voltage ■ is higher than the reference voltage E1, the error output of the error 7 amplifier 7 becomes negative, and the cutoff adjustment circuit 3 operates to lower the DC level of the Y signal. do. Note that the output of the error amplifier 7 is applied to the adder 3 by the hold circuit HOL at times other than the reference pulse period. As a result, the base voltage of the transistor Q1 decreases, the base voltage of the transistor Q3 increases, and the cathode voltage also increases, so that the cathode current (2) decreases and the detection voltage (2) also decreases.

On the other hand, when the cathode current IK is small and the voltage V is lower than the reference voltage E1, the error output of the error amplifier 7 becomes positive and operates to raise the DC level of the Y signal. As a result, the base voltage of the transistor Q1 increases, the base voltage of the transistor Q3 decreases, and the cathode voltage also decreases, so that the cathode current I increases and the detection voltage ■ also increases.

As a result of the above, during the period of the reference pulse, the circuit operates so that {circle around (2)} and El become equal, and the cathode current I becomes stable. At this time, it becomes stable at IK=E1/R2. This cathode current exists as a cutoff reference current even at times other than the reference pulse period.

If the above circuit is used not only for the R axis but also for the G axis and B axis, the cathode current detection resistor (R2
It is possible to correspond to various white balances by changing the ratio of (corresponding to). Therefore, the three-axis cathode current ratio can be set to white balance when the screen is dark. In other words, the cutoff points of the three axes can be aligned to achieve white balance.

However, in such an automatic cutoff control circuit, a feedback circuit is provided in the signal path to perform cutoff control, so it cannot be used for devices with a video band exceeding 100 MHz, such as high-definition CRT display devices. There was a problem in that the frequency characteristics deteriorated, making it difficult to obtain a predetermined basic performance.

(Problems to be Solved by the Invention) As mentioned above, in the conventional automatic cutoff control circuit,
Since a feedback circuit is provided in the signal path to perform cutoff adjustment, there is a drawback that frequency characteristics deteriorate, making it impossible to use in high-definition display devices.

Therefore, the present invention performs cutoff adjustment outside the signal path,
It is an object of the present invention to provide an automatic cutoff control circuit that can prevent deterioration of frequency characteristics.

[Structure of the Invention] (Means for Solving the Problems) The automatic cutoff control circuit of the present invention is characterized in that a reference pulse serving as a reference for cut I/off adjustment is inserted into a predetermined horizontal scanning period in a vertical blanking period. video output means for supplying the video signal to the cathode of the color cathode ray tube; cathode current detection means for detecting the cathode current of the color cathode ray tube; and comparison of the detected voltage from the cathode current detection means with a reference voltage. and an error detection means for extracting an error voltage, a sample hold means for sample-holding the error output from the error detection means in synchronization with the reference pulse, and each axial force of the video output means and the color cathode ray tube. A DC component cutting capacitor is disposed between the DC regeneration means and the DC regeneration means which applies a DC voltage to the signal passed through the capacitor, and the DC voltage is adjusted according to the error voltage output from the sample hold means. and means for controlling the DC voltage supplied to the regeneration means.

(Function) In the present invention, a feedback circuit for cutoff adjustment is not provided in the signal path, and the signal component is directly supplied to the cathode of the CRT via the DC component cutting capacitor. For cutoff adjustment, a DC reproduction voltage is created according to the cathode current detection voltage, and this reproduction voltage is applied to the signal after the DC component has been cut. Thereby, the cutoff point can be stabilized without deteriorating the frequency characteristics of a high-definition display device.

(Example) Examples will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an automatic cutoff control circuit according to an embodiment of the present invention.

In FIG. 1, the same components as in FIG. 2 will be described with the same reference numerals. For simplicity, only one axis (B axis) is shown, but it goes without saying that similar control circuits are configured for the B axis and the G axis. As in the case of FIG. 2, the Y signal with a reference pulse inserted is input to the input terminal 1, and the RY signal is input to the input terminal 2, and both signals are supplied to the video output circuit 5. The video output circuit 5 includes a transistor Q
1.

A matrix section consisting of Q2 and resistor R1, and a diode D
1 and a resistor R3, and an output section consisting of transistors Q3 and Q4 and a cathode current detection resistor R2. The R signal from the video output circuit 5 is supplied to the R-axis power sword of the CRT 6 through a DC regeneration circuit 9 consisting of a DC cut capacitor 8 and a diode D2. The voltage VK obtained at the cathode current detection resistor R2 is supplied to one terminal of the error amplifier 7, and the reference voltage E applied to its child terminal is
1. The error output of the error amplifier 7 is connected to the switch S.
The signal is amplified by an amplifier circuit 10 through a sample hold circuit 4 consisting of a WI and a bold circuit HOL, and is supplied to the cathode of a diode D2 of a DC reproduction circuit 9 as a DC reproduction signal. This diode D2 clamps the signal after the DC component is cut to the DC signal level of the amplifier circuit 10. In addition, the amplifier circuit 1° is
The output of the sample hold circuit 4 is input to the base of the transistor Q5, the emitter of Q5 is connected to the reference potential point via the resistor R4, and the collector is connected to the reference potential point via the resistor R4.
5 to the DC power supply 1B, its collector output is input to the base of the transistor Q6, the emitter of Q6 is connected to the DC power supply 1B through the resistor R6, and its collector is connected to the base 2I! ! It is connected to a potential point and has a configuration in which the emitter output of Q6 is supplied to the cathode of diode D2.

In the above configuration, when the cathode current I is large and the voltage VK is higher than the reference voltage E1, the error output of the error amplifier 7 becomes negative, and this error is input to the sample bold circuit P84 during the reference pulse period, and the bold The output decreases and is amplified by the amplifier circuit 10, thereby operating to increase the DC reproduction level of the DC reproduction circuit 9. As a result, the cathode current 1k is reduced and the detection voltage is also reduced to ■.

On the other hand, when the cathode current I becomes small and the voltage V is lower than the reference voltage E1, the error output of the error amplifier 7 becomes positive, and the DC regeneration circuit 9 operates to lower the DC regeneration level. As a result, the cathode current 1k is increased and the detection voltage VK is also increased.

As a result of the above, the circuit operates so that {circle around (2)} and El become equal, and the cathode current IK is stabilized. At this time, the cathode current Ik is stabilized at IK = E1 /R2. This cathode current exists as a cutoff reference current even at times other than the reference pulse period.

Conventionally, cutoff adjustment was performed by adding the output of the sample bold circuit 4 to the Y signal in the adder 3 in the Y signal path, but in this embodiment, the output of the sample bold circuit &184 is amplified. After being amplified by the circuit 10, the signal is added to the signal passed through the capacitor 8 of the DC regeneration circuit F#I9, thereby regenerating the DC component. That is, the DC component is once cut in the signal path, and the cutoff adjustment is performed by controlling the DC reproduction level in the DC reproduction circuit 89.The signal component is directly supplied to the CRT 6 via the capacitor 8, so that the image There are no operating point fluctuations or dynamic range fluctuations of the amplifier circuit, and therefore no deterioration of frequency characteristics.

[Effects of the Invention] As described above, according to the present invention, the cutoff adjustment is performed by controlling the DC reproduction level, so the cutoff adjustment is performed outside the signal path. As a result, even in a high-definition display device, its frequency characteristics do not deteriorate, and it is possible to stabilize not only cut-off performance but also white balance performance. Also in the manufacturing process, the white balance adjustment time can be reduced and the number of man-hours can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an automatic cut-off control circuit according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional automatic cut-off control circuit, and Fig. 3 is a circuit diagram showing a conventional automatic cut-off control circuit. FIG. 2 is a waveform diagram showing signal waveforms. 1... Y signal input terminal into which reference pulse is inserted, 2
... input terminal for color difference signal, 4 ... sample bold circuit, 5 ... video output circuit, 6 ... CRT, 7 ... error amplifier, 8 ... capacitor for DC component cut, 9. ...DC regeneration circuit, 10...amplifier circuit R2...
Cathode current detection circuit, El...Reference voltage, D2...Diode. Figure 2 (b) KiH) Kubals dimension 1-1 Figure 3

Claims (1)

[Scope of Claims] Video output means for supplying a video signal in which a reference pulse serving as a reference for cutoff adjustment is inserted in a predetermined horizontal scanning period in a vertical blanking period to a cathode of a color cathode ray tube; a cathode current detection means for detecting the cathode current of the color cathode ray tube; an error detection means for comparing the detected voltage from the cathode current detection means with a reference voltage and extracting an error voltage; and an error output from the error detection means. , a sample hold means for holding a sample in synchronization with the reference pulse; a DC component cutting capacitor disposed between the video output means and the cathode of the color cathode ray tube; An automatic cut characterized by comprising a DC regeneration means for adding a DC voltage to the sample and hold means, and a means for controlling the DC voltage supplied to the DC regeneration means according to the error voltage output from the sample hold means. Off control circuit.