JPH0531463U - Screen erase circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Eliminates screen disturbance when switching any horizontal or vertical sync frequency of a multi-frequency compatible display. [Structure] A DC voltage 1 that changes in proportion to a horizontal or vertical synchronizing frequency is used as one input, the DC voltage 1 is passed through an integrating circuit consisting of a resistor 4 and a capacitor 5, and the integrated output voltage is used as the other input. A comparator 6 is provided, and a change in the DC voltage 1 is taken out as a pulse for a fixed period and output as an output of the comparator 6. This pulse controls the blanking circuit, the contrast or the bright of the video amplifier circuit. [Effect] Since the disturbance of the screen at the time of switching the arbitrary horizontal or vertical synchronizing frequency is eliminated, it is possible to protect the fluorescent film of the picture tube and eliminate the discomfort caused by the disturbance of the screen.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a multi-scan display capable of receiving signals of different horizontal or vertical sync frequencies, and more particularly to a circuit for eliminating screen disturbance when switching horizontal or vertical sync frequencies.

[0002]

[Prior Art]

 As described in Japanese Patent Application Laid-Open No. 62-76971, a conventional circuit stops horizontal deflection at the time of switching the horizontal synchronizing frequency and mutes the video signal to prevent a phenomenon in which a vertical bright line appears. Protects the fluorescent film of the picture tube.

[0003]

[Problems to be solved by the device]

 The above-mentioned conventional technique has a problem that no consideration is given to switching of the vertical frequency and switching of an arbitrary frequency.

An object of the present invention is to eliminate screen disturbances such as bright lines during vertical frequency switching and during arbitrary frequency switching.

[0005]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention uses a DC voltage (hereinafter referred to as fv voltage) that changes in proportion to a horizontal or vertical synchronizing frequency as one input, inputs the fv voltage into an integrating circuit, and outputs the output of the integrating circuit. A comparator with a voltage as the other input was provided, and the image output circuit was controlled by the signal output from this comparator to eliminate screen disturbance when switching the horizontal or vertical sync frequency.

[0006]

[Action]

 The fv voltage is applied to one input terminal of the comparator, and the fv voltage that has passed through the product circuit is input to the other input terminal. The fv voltage changes when the horizontal or vertical sync frequency is switched, and the voltage on the other terminal side that has passed through the integrator circuit changes more slowly than the voltage input directly to the comparator. The signal of can be taken out at the comparator output. By applying this pulse-shaped signal to a circuit such as contrast, bright or blanking in the image amplification circuit, the disturbance on the screen can be eliminated.

[0007]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. 1, 2 and 3.

Referring to FIG. 1, first, a case will be described in which the signal is switched to a signal having a higher horizontal or vertical synchronizing frequency than the signal being received. The horizontal or vertical fv voltage input from the terminal 1 is divided by the voltage dividing resistors 2 and 3 and applied to the non-inverting input terminal of the operational amplifier 6 used as a comparator. The fv voltage is applied to the inverting input terminal of the operational amplifier 6 via an integrating circuit composed of the resistor 4 and the capacitor 5. Therefore, when receiving a signal of a certain horizontal or vertical sync frequency, the voltage at the non-inverting input terminal is lower than the voltage at the inverting input terminal, so the voltage at the output terminal of the operational amplifier 6 is in the range of A in FIG. Then, it becomes the earth potential. Here, when the signal is switched to a signal whose horizontal or vertical synchronizing frequency is higher than the received signal, the fv voltage input to the non-inverting input terminal of the operational amplifier 6 becomes high. However, since the fv voltage applied to the inverting input terminal passes through the integrator circuit, it rises later than the voltage applied to the non-inverting input terminal. Therefore, at the time of signal switching, the voltage at the non-inverting input terminal of the operational amplifier 6 temporarily becomes higher than the voltage at the inverting input terminal, as shown by the range B in FIG. 2, and the voltage at the output terminal of the operational amplifier 6 is Vcc. It becomes a level. Then, after a certain period of time, the voltage applied to the inverting input terminal of the operational amplifier 6 becomes higher, as in the range C of FIG. 2, so that the voltage of the output terminal of the operational amplifier 6 becomes the original ground potential.

Next, a case will be described in which the signal is switched to a signal whose horizontal or vertical synchronizing frequency is lower than that of the signal being received. The horizontal or vertical fv voltage input from the terminal 1 is applied to the inverting input terminal of the operational amplifier 12 via the resistor 11. The voltage is divided by the resistors 8 and 9 and applied to the non-inverting input terminal of the operational amplifier 12 via the integrating circuit including the capacitor 10. Therefore, when receiving a signal of a certain horizontal or vertical synchronizing frequency, the voltage at the non-inverting input terminal of the operational amplifier 12 is lower than the voltage at the inverting input terminal, so the voltage at the output terminal of the operational amplifier 12 is as shown in FIG. As in the range of A, it becomes the ground potential. Here, when the signal is switched to a signal whose horizontal or vertical synchronizing frequency is lower than the received signal, the fv voltage applied to the inverting input terminal of the operational amplifier 12 becomes low. However, since the fv voltage applied to the non-inverting input terminal goes through the integrating circuit, the rising edge becomes slower than the fv voltage applied to the inverting input terminal. Therefore, at the time of signal switching, the voltage at the non-inverting input terminal of the operational amplifier 12 temporarily becomes higher than the voltage at the inverting input terminal, as shown by the range B in FIG. 3, so the voltage at the output terminal of the operational amplifier 12 is at the Vcc level. Becomes

The outputs of the operational amplifier 6 and the operational amplifier 12 are added via the backflow prevention diodes 7 and 13, respectively. The added signals are divided by resistors 14 and 15 and applied to the base of transistor 17. The resistor 16 is a current limiting resistor of the transistor 17. Here, when the Vcc level signal is output from the operational amplifier 6 or 12, the transistor 17 is turned on, and the video signal 19 is set to the ground potential via the backflow prevention diode 18. That is, when the horizontal or vertical synchronizing frequency is switched, the video signal becomes the ground potential for a certain period of time, and the image disturbance until the horizontal or vertical synchronizing is pulled in can be eliminated.

The above-described embodiment is a method in which the output of the operational amplifier is directly added to the video signal. Alternatively, it is controlled by a video circuit such as the G1 terminal of the CRT, blanking, bright and contrast. However, the same result can be obtained.

[0012]

[Effect of the device]

 According to the present invention, the disturbance of the screen can be eliminated by switching the horizontal or vertical sync frequency arbitrarily, so that the fluorescent film of the picture tube is protected and the discomfort caused by the disturbance of the screen at the time of switching is eliminated. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the circuit according to the embodiment of the present invention.

FIG. 3 is an operation waveform diagram of a circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1. fv voltage, 4. 4. resistance of integrating circuit, 5. Capacitor of integrating circuit, Comparator, 8. The resistance of the integrating circuit, 10. Capacitor of integrating circuit, 12. comparator.

Claims (1)

[Scope of utility model registration request] 1. A multi-scan display capable of receiving signals of different horizontal or vertical synchronizing frequencies, wherein one input is a DC voltage which changes in proportion to the horizontal or vertical synchronizing frequency, and the horizontal or vertical A direct current voltage that changes in proportion to the synchronization frequency is input to the integrating circuit, and a comparator that uses the output voltage of the integrating circuit as the other input is provided, and with the signal output from the comparator,
A screen erasing circuit for erasing a screen disturbance at the time of switching the horizontal or vertical synchronizing frequency by controlling an image amplification circuit.