JPH10224663A - S/n improving device for video equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the S/N by reducing the effect of switching noise even in the case of the video equipment using a switching power supply. SOLUTION: A lead phase gate signal generating circuit 1a generates lead phase gate signal S3 that is logical 1 for a prescribed period from a front edge of a horizontal synchronizing signal (negative polarity) S1, and a lagged phase gate signal generating circuit 1b generates a lagged phase gate signal S4 that is logical 1 for a prescribed period from the front edge of the horizontal synchronizing signal S1. AND circuits 2a, 2b AND the advanced phase gate signal S3 and a control pulse S2 of a switching power supply and the lagged phase gate signal S4 and the control pulse S2. As a result, a lead phase signal S5 and a lagged phase signal S6 are outputted. The lead phase signal S5 produces a positive power supply S7 and the lagged phase signal S6 produces a negative power supply S8 and an adder circuit 4 adds the positive and negative power supplies. An output of the adder circuit 4 is integrated by an integration circuit 5 and an output voltage S9 controls a voltage controlled oscillator VCO 6. An output S10 of the VCO 6 is made in phase to the control pulse S2 of the switching power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an S / N improvement device for video equipment, such as a CCD television camera, which reduces the influence of switching noise from a switching power supply.

[0002]

2. Description of the Related Art In video equipment such as a CCD television camera, a small, lightweight and efficient switching power supply is preferably used. However, since the switching frequency of the switching power supply is fixed, if the phase relation with the synchronization frequency of the video signal becomes constant, there is a possibility that a substantially fixed periodic noise is generated on the screen.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. Even in a video equipment using a switching power supply, the influence of switching noise is reduced by reducing the influence of switching noise.
It is intended to provide a technique for improving N.

[0004]

A phase difference detecting circuit for detecting a phase difference between a synchronous signal of a video signal handled by the video device and a switching frequency of a power supply, and a control voltage for changing the switching frequency when the phase difference is small. And a VCO (Voltage Controlled Oscillator) that changes the same frequency by the control voltage. When the phase difference is small, the switching frequency is changed so that the phase of the synchronization frequency matches the switching frequency. In this case, the effect of switching noise on the video signal is reduced.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a video equipment such as a CCD television camera using a switching application, a phase difference for detecting a phase difference between a synchronization signal of a video signal handled by the video equipment and a switching frequency of the power supply. A detection circuit, a control voltage generation circuit for generating a control voltage for changing the switching frequency when the phase difference is small, and a VCO for changing the same frequency by the control voltage are provided. To change.

When the phase difference becomes equal to or less than a predetermined value, the control voltage is generated.

[0007] A circuit is provided for discriminating and detecting when the phase difference is advanced or delayed with respect to the synchronization signal of the video signal. When the phase difference is advanced, the switching frequency is lowered. When the phase is late, control is performed to increase the value.

A leading gate signal generating circuit having a logic 1 for a certain period before the leading edge of the video signal synchronizing signal, a lagging gate signal generating circuit having a logic 1 for a certain period after the leading edge of the synchronizing signal, An AND circuit for each of the in-phase gate signal and the lag gate signal and the control pulse of the switching power supply,
A positive power supply circuit and a negative power supply circuit generated at the output of each AND circuit, an addition circuit of the same positive power supply and the negative power supply, and an integration circuit of an output voltage of the addition circuit are provided. Control the VCO.

In a video device such as a CCD television camera using a switching application, a frequency control unit for changing the switching frequency of the power supply is provided so that the switching frequency is constantly changed.

The change of the switching frequency is performed in the cycle of the AC power supply using the pulsation of the AC power supply.

[0011]

1 is a (A) schematic block diagram and (B) a timing chart of a main part of an embodiment of an S / N improving apparatus for video equipment according to the present invention. An advanced gate signal generating circuit 1a generates an advanced gate signal S3 which becomes a logical 1 for a certain period from a leading edge of a horizontal synchronizing signal (negative polarity) S1 of a video signal of a CCD television camera or the like. The phase advance gate signal generation circuit 1a is, for example, a monostable multivibrator (hereinafter referred to as MM).
Then, the output is delayed for a certain period from the horizontal synchronizing pulse one cycle before, and the output thereof produces another phase leading gate signal S3 which becomes logic 1 for the certain period. Similarly, the delayed gate signal S4 which becomes logic 1 for a certain period after the leading edge of the horizontal synchronizing signal S1,
It is created by the late gate signal generation circuit 1b. The delay gate signal generation circuit 1b can be constituted by a circuit that generates a pulse that becomes logic 1 for a certain period by MM triggered at the leading edge of the horizontal synchronization signal S1, for example. The control pulse S of the switching power supply for each of the advanced gate signal S3 and the delayed gate signal S4
Between the two, the logical product is obtained by the logical product circuits 2a and 2b. As a result, when the control pulse S2 of the switching power supply is advanced from the horizontal synchronizing signal and is within the above-mentioned predetermined period, the advanced signal S5 is output.
Is output. The positive power supply circuit 3a is controlled by the leading signal S5 to generate the positive power supply S7, and the negative power supply circuit 3b is controlled by the lagging signal S6 to obtain the negative power supply S8. The addition circuit 4 adds the positive power supply S7 and the negative power supply S8. The output is integrated by the integration circuit 5, and the VCO 6 is controlled by the output voltage S9. VCO6 is
For example, if the capacitance C, which is the time constant of the transmission circuit, is controlled by the voltage applied to the variable capacitance diode, if the voltage increases, C increases, the transmission frequency decreases, the phase of the switching frequency is delayed, and if the voltage increases, The transmission frequency increases and the phase of the switching frequency advances. Therefore,
Assuming that the output S10 of the VCO 6 has the same phase as the control pulse S2 of the switching power supply, if the phase of the switching frequency matches within the above-mentioned fixed period of the horizontal synchronizing signal,
The phase of the switching frequency is adjusted, and the two phases are shifted. The same operation and effect can be obtained even when the horizontal synchronization signal S1 is used as a vertical synchronization signal.

FIG. 2 is a schematic block diagram of another embodiment of the S / N improvement apparatus for video equipment according to the present invention. The AC power supply S21 is rectified by the rectifier 21 and the small-capacity capacitor 22 to obtain a pulsating voltage S22. The pulsation voltage S22 is adjusted to an appropriate voltage by the variable resistor 23, and the VCO 26 is controlled.
V which is a frequency that fluctuates periodically with the frequency of the power supply S21
The output S10 of the CO 26 is obtained. The output S10 is used as a control pulse for controlling a switching application of a video device such as a CCD television camera, so that the switching frequency is constantly changed.

[0013]

According to the present invention, a phase difference detection circuit for detecting a phase difference between a synchronization signal of a video signal handled by the video equipment and a switching frequency of the power supply, and a control voltage for changing the switching frequency when the phase difference is small. And a VCO that changes the same frequency by the same control voltage. When the same phase difference is small, the switching frequency is changed so that the phase of the synchronization frequency and the switching frequency can be avoided. Therefore, the influence of switching noise on the video signal can be reduced, and the effective S / N of the video signal is improved.

[Brief description of the drawings]

FIG. 1A is a schematic block diagram of an embodiment of an S / N improvement device for a video device according to the present invention, and FIG.

FIG. 2 is a schematic block diagram of another embodiment of the S / N improvement device for video equipment according to the present invention.

[Explanation of symbols]

 S1 Horizontal synchronization signal S2 Control pulse S3 Early phase gate signal S4 Late phase gate signal S5 Early phase signal S6 Late phase signal 1a Advance phase gate signal generation circuit 1b Slow gate signal generation circuit 2a, 2b AND circuit 3a Positive power supply circuit 3b Negative power supply circuit 4 Adder circuit 5 Integrator circuit 6 VCO (Voltage Controlled Oscillator) S21 AC power supply 21 Rectifier 22 Capacitor 23 Variable resistor 26 VCO

Claims (6)

[Claims] 1. A phase difference detection circuit for detecting a phase difference between a synchronization signal of a video signal handled by the video device and a switching frequency of the power supply in a video device such as a CCD television camera using a switching device. A control voltage generating circuit that generates a control voltage that changes the switching frequency when the phase difference is small; and a VCO (Voltage Controlled Oscillator) that changes the frequency by the control voltage.
and the switching frequency is changed when the phase difference is small.
N improvement device. 2. The apparatus according to claim 1, wherein the control voltage is generated when the phase difference becomes equal to or less than a predetermined value. 3. A circuit for discriminating and detecting a case where the phase difference is advanced from a synchronization signal of the video signal and a case where the phase difference is delayed, the switching frequency is determined when the phase difference is advanced. 3. The apparatus according to claim 2, wherein the S / N ratio is controlled so as to be lower and to be higher when the phase is late. 4. A leading gate signal generating circuit which becomes logic 1 for a certain period before the leading edge of the synchronizing signal of the video signal, and a lagging gate signal generating circuit which becomes logic 1 for a certain period after the leading edge of the synchronizing signal. And an AND circuit of the control pulse of the switching power supply and each of the synchronous phase gate signal and the late phase gate signal, a positive power supply circuit and a negative power supply circuit generated at an output of each AND circuit, A negative power addition circuit,
4. An apparatus according to claim 3, further comprising an integrating circuit for the output voltage of the adding circuit, wherein the output of the integrating circuit controls the VCO. 5. In a video equipment such as a CCD television camera using a switching application, a frequency control unit for changing a switching frequency of the power supply is provided so that the switching frequency is constantly changed. S / N improvement device for video equipment. 6. The change of the switching frequency is AC
7. The apparatus according to claim 6, wherein the pulsation of the power supply is used in the cycle of the AC power supply.