JPH07222024A - Image display device having vertical amplitude stabilizing circuit - Google Patents

Abstract

PURPOSE:To eliminate vertical size fluctuation due to noise or the like and to reduce a time till the vertical size at signal changeover is made stable. CONSTITUTION:The image display device is provided with a frequency /voltage conversion circuit 301 generating a voltage in response to a vertical synchronizing signal with a different frequency and a vertical amplitude stabilizing circuit 306 having plural integration circuits 302, 303 whose time constant is different to make the fluctuation of an output voltage of the circuit 301 stable, a buffer circuit 305 connecting outputs of the circuits 302, 303 to a vertical amplitude control circuit, a switching means 304 selecting either of the integration circuits, and a control circuit 308 controlling the operating time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical amplitude stabilizing circuit for a display device such as a multi-scan display which operates by inputting vertical synchronizing signals of different frequencies.

[0002]

2. Description of the Related Art FIG. 3 shows a block diagram of a multi-scan display, and FIG. 4 shows a block diagram around a vertical excitation circuit shown in FIG. FIG. 5 shows a conventional technique of the vertical amplitude stabilizing circuit in FIG.

In FIG. 5, the frequency / voltage conversion circuit 1 outputs a voltage according to the frequency of the input vertical synchronizing signal as shown in FIG. If this output voltage becomes unstable due to noise or the like, the vertical size changes.

In order to suppress the fluctuation, it is stabilized by an integrating circuit 11 composed of a resistor 3 and a capacitor 4.

When the capacity of the capacitor 4 is small, that is, when the time constant of the integrating circuit 11 is small (the time constant at this time is T1), the output 2 of the frequency / voltage converting circuit 1 is shown in FIG. When such noise is superimposed, the emitter output waveform 7 of the transistor 6 fluctuates as shown in FIG. Therefore, if the capacitance of the capacitor 4 is increased, that is, the time constant of the integrating circuit 11 is increased (the time constant at this time is T2), the capacitor becomes stable as shown in FIG. 8C. The time constants T1 and T2 are T1 <T2.

However, when the time constant of the integrating circuit 11 is T2 and the output 2 of the frequency / voltage converting circuit 1 changes as shown in FIG. 9A when the input signal is switched, the emitter output waveform 7 of the transistor 6 is As shown in (C) of 9, it takes time to stabilize. If the time constant of the integrating circuit 11 is T1, the time until it becomes stable becomes short as shown in FIG. 9B.

Alternatively, as in Japanese Patent Laid-Open No. 1-114165, an integrating circuit in the frequency / voltage converting circuit is used instead.

[0008]

In the above-mentioned prior art, there is no choice but to give priority to the speed of vertical screen response at the time of signal switching or to prevent vertical size fluctuation due to noise or the like. It was

An object of the present invention is to eliminate vertical size variation due to noise and the like, and to shorten the time until the vertical size stabilizes at the time of signal switching.

[0010]

The above object is to provide an integrating circuit having a large time constant for stabilizing the output voltage of the frequency / voltage conversion circuit and an integrating circuit having a small time constant for giving priority to the vertical size screen response speed. And a switching circuit for switching the integration circuit and a control circuit for switching the output of the switching device when switching the input signal.

The above object is also achieved by providing a circuit for automatically switching the switching means by the output of the integrating circuit when the signal is switched.

[0012]

The control circuit of the vertical amplitude stabilizing circuit of the present invention is shown in FIG.
As shown in, when switching the vertical synchronizing signal, the output voltage of the integrating circuit 303 is connected to the buffer circuit only for the time until the output voltage of the integrating circuit 302 stabilizes according to the change of the output voltage of the frequency / voltage converting circuit. Switching the switching means. After that, when the output voltage of the integrating circuit 302 becomes stable, the switching means is switched so that the output voltage of the integrating circuit 302 is connected to the buffer circuit. Here, the time constant of the integrating circuit 302 is set so that the output voltage can be stabilized against variations in the input voltage. The time constant of the integrating circuit 303 is made sufficiently smaller than that of the integrating circuit 302.

As a result, it is possible to reduce the vertical size variation at the time of signal switching, and to prevent the vertical size variation from being caused by external noise in the steady state.

FIG. 2 also shows a method in which the switching means itself has the same function as the above control circuit. When the vertical synchronizing signal is switched, the integration circuit 303 stabilizes quickly until the output voltage of the integration circuit 302 stabilizes in accordance with the change in the output voltage of the frequency / voltage conversion circuit. The output voltage of is connected to the buffer circuit. Then, the integrating circuit 302
The object can be achieved by switching the switching means so that the output voltage of the integrating circuit 302 is connected to the buffer circuit when the output voltage of 1 is sufficiently stabilized.

[0015]

FIG. 6 shows an embodiment of the present invention.

The frequency / voltage conversion circuit 1 outputs a voltage corresponding to the frequency of the input vertical synchronizing signal.

The output is stabilized by eliminating the voltage fluctuation due to noise etc. by an integrating circuit 11 composed of a resistor 3 and a capacitor 4. The time constant of the integrating circuit 11 is equal to the integrating circuit 1
It should be larger than the time constant of 6. The voltage stabilized by the integrating circuit 11 is input to the vertical amplitude control circuit 10 via the transistor 6.

When the input signal is switched from the low frequency to the high frequency and the output voltage of the frequency / voltage conversion circuit 1 changes as shown in FIG. 10A, the output of the integration circuit 11 has a large time constant, and therefore the output of FIG. The output voltage does not become constant instantaneously as in (B). During this period, the integrating circuit 16 having a small time constant rises as shown in FIG.
The transistor 12 is turned on for the period shown in FIG.
The voltage stabilized by the integrating circuit 16 as shown in (E) is input to the vertical amplitude control circuit.

On the contrary, when the signal is switched from the high frequency to the low frequency, the output voltage of the frequency / voltage conversion circuit 1 is lowered, so that the charge accumulated in the capacitor 4 through the diode 17 is integrated into the integration circuit 16 having a small time constant. The time during which the output of the integrator circuit 11 becomes constant by further discharging is shortened, and the stabilized voltage is input to the vertical amplitude control circuit as soon as possible.

According to the present invention, there is an effect that an inexpensive circuit eliminates vertical size variation due to noise and the like, and shortens the time until the vertical amplitude stabilizes at the time of signal switching.

[0021]

As described above, according to the present invention, the frequency
It is possible to stabilize the output of the voltage conversion circuit and shorten the time for the vertical amplitude to stabilize during signal switching.

[Brief description of drawings]

FIG. 1 is a diagram showing a vertical amplitude stabilization circuit 1.

FIG. 2 is a diagram showing a vertical amplitude stabilizing circuit 2;

FIG. 3 is a block diagram of a multi-scan display.

FIG. 4 is a block diagram around a vertical excitation circuit.

FIG. 5 is a diagram showing a conventional technique of a vertical amplitude stabilizing circuit.

FIG. 6 is a diagram showing an embodiment of a vertical amplitude stabilizing circuit of the present invention.

FIG. 7 is a characteristic diagram of input / output of the frequency / voltage conversion circuit 1.

FIG. 8 is a waveform diagram when noise is superimposed on the output of the frequency / voltage conversion circuit.

FIG. 9 is a waveform diagram when signals are switched.

FIG. 10 is a waveform chart of each part in the vertical amplitude stabilization circuit.

[Explanation of symbols]

 1 ... Frequency / voltage conversion circuit, 3 ... Resistor, 4 ... Capacitor, 6 ... Transistor, 8 ... Resistor, 9 ... Resistor, 10 ... Vertical amplitude control circuit, 11 ... Integrating circuit, 12 ... Transistor, 13 ... Resistor, 14 ... Resistor, 15 ... Capacitor, 16 ... Integrator circuit, 17 ... Diode, 103 ... External signal input circuit, 102 ... Signal switching circuit, 103 ... Video circuit / video output circuit, 104 ... Multi-frequency compatible sync signal control circuit, 105 ... CRT Drive circuit, 106 ... High-voltage rectification output circuit / focus circuit, 107 ... Vertical excitation / vertical output circuit, 108 ... Horizontal excitation / horizontal output circuit, 201 ... Vertical size adjustment circuit, 202 ... External input interface circuit, 203 ... Frequency / voltage Conversion circuit, 204 ... Vertical amplitude stabilization circuit, 205 ... Multi-frequency compatible synchronization signal system Circuits, 206 ... Vertical excitation circuit, 207 ... Vertical amplitude control circuit, 208 ... Vertical output, 209 ... Linearity control circuit, 210 ... Vertical position control circuit, 301 ... Frequency / voltage conversion circuit, 302 ... Integrating circuit, 303 ... Integral Circuit, 304 ... Switching means, 305 ... Buffer circuit, 306 ... Vertical amplitude stabilizing circuit, 307 ... Vertical amplitude control circuit.

Claims (2)

[Claims] 1. A frequency / voltage conversion circuit for generating a voltage corresponding to a vertical synchronizing signal having a different frequency, a plurality of integration circuits having different time constants for stabilizing fluctuations of its output voltage, and its output to a vertical amplitude control circuit. An image display device having a vertical amplitude stabilizing circuit, comprising a buffer circuit to be connected, switching means for switching the integrating circuit, and a control circuit for controlling the operation time thereof. 2. An image display device having a vertical amplitude stabilizing circuit according to claim 1, wherein the switching means is automatically switched by the output voltage of the integrating circuit.