JPH08294042A - Video camera equipment - Google Patents

Abstract

PURPOSE: To reduce dot disturbance in a video image by selecting a clock signal that is used for generating a vertical synchronizing signal and a horizontal synchronizing signal from clock signals of generating sources different from a vertical blanking period and a vertical scanning period in the monitor video camera of the power supply synchronization system. CONSTITUTION: A voltage controlled oscillator circuit 3 is controlled on the basis of phase comparison between a vertical synchronizing signal S2 and a power synchronization pulse S1 at a phase comparator section 2. The voltage controlled oscillator circuit 3 oscillates a clock signal of a required frequency based on the control concerned. The circuit is a 1st clock signal. A 2nd clock signal is obtained from a crystal oscillator circuit 4. A changeover circuit 5 switches the signal between the 1st clock signal and the 2nd clock signal. The 1st clock signal is selected for the vertical blanking period and the 2nd clock signal is selected for the vertical scanning period through the changeover as above. The changeover is controlled by a changeover control section 7 on the detection of the vertical blanking period by a vertical blanking period detection section 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera device, and more particularly to a power-synchronization type surveillance video camera, in which a clock signal used for generating a vertical synchronizing signal and a horizontal synchronizing signal is vertically retraced. The present invention relates to a video camera device capable of reducing dot interference in an image by switching to clock signals of different generation sources in a period and a vertical scanning period.

[0002]

2. Description of the Related Art It is well known that, in a camera monitoring apparatus having a plurality of video cameras, which are switched and displayed on a monitor, there is a power supply synchronization method as a method for preventing disturbance of vertical synchronization when the cameras are switched. On the street. In this system, the synchronization between the cameras is maintained by synchronizing the vertical synchronization of each camera with an AC power supply of a commercial frequency, which is the power supply of the monitoring device. Specifically, a vertical synchronization signal generated inside each camera is compared in phase with a power supply synchronization pulse signal generated based on the AC power supply, and a voltage-controlled oscillation that oscillates a clock signal based on this phase comparison. The phase of the circuit is controlled, and a clock signal generated under the control is used as a reference signal for generating the vertical synchronizing signal. This loop holds the synchronization between the vertical synchronizing signal and the power supply.

However, the above-mentioned oscillation method in the power supply synchronization system has a drawback that dot interference (interference due to color subcarrier) occurs on an image. This is because in the case of the voltage control type clock signal oscillation circuit, there is a certain limit in the phase (frequency) control, and it is difficult to perform the phase control to make dot interference inconspicuous. Therefore, in order to reduce this dot interference, a highly stable oscillation method is required, and a crystal oscillator is an oscillation method suitable for this. In view of this point,
Some cameras use the above-mentioned crystal oscillation method instead of the voltage-controlled oscillation method for clock signal generation, but in this case the above-mentioned power supply synchronization becomes impossible, and when switching between multiple cameras and monitoring. Causes vertical disturbance when switching. On the other hand, there are cameras equipped with both the voltage-controlled oscillation method and the crystal oscillation method, but in this camera as well, either one is selected and fixed, so that either vertical synchronization disturbance or dot interference remains. Becomes Conventional video cameras have such drawbacks.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to provide a video camera device which is capable of reducing dot interference while maintaining the power supply synchronization system. And

[0005]

SUMMARY OF THE INVENTION The present invention is controlled so as to be synchronized with an AC power source of a commercial frequency, and has a first frequency of a required frequency.
And a second clock signal generating means for generating a second clock signal having a frequency substantially the same as that of the clock signal asynchronously with the AC power supply, First clock signal and second
And a switching control signal for switching the switching circuit so as to select the first clock signal in the vertical blanking period and select the second clock signal in the vertical scanning period. The present invention provides a video camera device comprising switching control signal generating means for generating the vertical synchronizing signal and horizontal synchronizing signal based on the clock signal selected by the switching circuit.

[0006]

The phase comparator compares the phase of the vertical synchronizing signal and the power supply synchronizing pulse, and controls the voltage controlled oscillator circuit based on the phase comparison. Based on the control, the voltage controlled oscillator circuit oscillates a clock signal having a required frequency. This becomes the first clock signal. The second clock signal is obtained from the crystal oscillator circuit. A switching circuit switches between the first clock signal and the second clock signal. This switching is performed so as to be on the first clock signal side during the vertical blanking period and on the second clock signal side during the vertical scanning period. This switching is controlled by the switching control unit based on the vertical blanking period detection by the vertical blanking period detection unit. As a result, the first clock signal synchronized with the power supply is selected in the vertical blanking period,
The second clock signal having a high stable frequency is selected in the vertical scanning period. A vertical synchronizing signal and a horizontal synchronizing signal are generated based on the selected clock signal, power source synchronization is maintained, and dot interference is reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A video camera device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an essential part showing an embodiment of a video camera device according to the present invention, and FIG. 2 is a correlation diagram between a first clock signal and a second clock signal within one vertical period (1V). In FIG. 1, reference numeral 1 denotes a sync signal generating section including a vertical sync signal generating section 1a and a horizontal sync signal generating section 1b, and 2 denotes a power supply synchronizing pulse signal S1 generated from an AC power supply of a commercial frequency which is a power source of the present apparatus. Sync signal generator
The phase comparison unit 3 for performing a phase comparison with the vertical synchronization signal S2 from 1a is controlled by the phase comparison unit 2 and has a first frequency of a required frequency.
Voltage controlled oscillator circuit (VC
O), 4 is a crystal oscillation circuit that oscillates the second clock signal C2 having the same frequency as the first clock signal C1, and 5 is a switching circuit that switches between the first clock signal C1 and the second clock signal C2, 6 Is a vertical blanking period detection unit that detects a vertical blanking period from the vertical synchronization signal from the vertical synchronization signal generation unit 1a,
7 is a switch for controlling to switch to the first clock signal C1 side in the vertical blanking period and to switch to the second clock signal C2 side in the vertical scanning period based on the detection signal from the vertical blanking period detection unit 6. It is a control unit.

Next, the operation of the present invention will be described. In the synchronizing signal generator 1, the vertical synchronizing signal is generated by the vertical synchronizing signal generator 1a and the horizontal synchronizing signal is generated by the horizontal synchronizing signal generator 1b based on the input clock signal C3. Among them, the vertical synchronization signal S2 is sent to the phase comparison unit 2 and is compared in phase with the power supply synchronization pulse signal S1 in the same phase comparison unit 2. This power supply synchronization pulse signal S1 is generated based on an AC power supply of a commercial frequency which is a power supply of this device. The phase comparator 2 generates a voltage signal according to the phase difference between the two signals, and controls the voltage controlled oscillator circuit 3 with this voltage signal. According to this control, the voltage controlled oscillator circuit 3 oscillates the first clock signal C1 having the required frequency. The frequency is, for example, 28 MHz if the video signal is of the NTSC system. The voltage controlled oscillator circuit 3 may be an oscillator circuit having a general LC configuration. The second clock signal C2 with respect to the first clock signal C1 is obtained by the crystal oscillation circuit 4 having excellent frequency stability. The oscillation signal generated by the crystal oscillator circuit 4 is independent and independent of the power supply. The first clock signal C1 and the second clock signal C2 are sent to the switching circuit 5, respectively.

On the other hand, the vertical sync signal generated by the vertical sync signal generator 1a is also sent to the vertical blanking interval detector 6. The vertical blanking interval detection unit 6 detects a vertical blanking interval based on this vertical synchronization signal. The purpose of this detection is to set the switching timing in the switching circuit 5. The detection signal detected by the detection unit 6 is sent to the switching control unit 7, and the switching control unit 7 outputs a required switching control signal S3. The required switching control signal S3 is the first clock signal C1 during the vertical blanking period.
The second clock signal C2 during the vertical scanning period.
This is a signal for switching to the side. This switching control signal S3
As a result, the switching circuit 5, as shown in FIG.
Is set to the a side and the first clock signal C1 is selected, and during the vertical scanning period T2, the second clock signal C2 is selected by switching to the b side. The clock signal C3 switched and selected by the switching circuit 5 is sent to the vertical synchronizing signal generating section 1a and the horizontal synchronizing signal generating section 1b of the synchronizing signal generating section 1 and serves as reference clocks for synchronizing signal generation.

Each of the synchronizing signal generators 1a and 1b divides the clock signal (for example, countdown by a counter) to generate a vertical synchronizing signal and a horizontal synchronizing signal. As a result, in one vertical cycle (1V), the vertical blanking period T1
Is a synchronization signal that maintains a synchronous relationship with the power supply synchronization pulse signal S1, and is a synchronization signal that follows a highly stable clock signal that is asynchronous with the power supply during the vertical scanning period T2. As a result, the synchronization with the power supply is maintained during the vertical blanking period, while the dot interference is reduced by the highly stable clock signal reference that is asynchronous with the power supply during the vertical scanning period. The VCO 3 when the second clock signal C2 is selected by the switching circuit 5 (b side) is the second
The oscillation control is performed based on the clock signal C2, but in this case, since it is not selected by the switching circuit 5, it has no effect.

[0011]

As described above, according to the present invention, in the surveillance video camera of the power supply synchronizing system, the clock signal necessary for generating the vertical synchronizing signal and the horizontal synchronizing signal is supplied with the power supply synchronizing signal in the vertical blanking period. It is possible to use a clock signal from the crystal oscillator circuit which is asynchronous with the power supply during the vertical scanning period. As a result,
Power supply synchronization is possible because the synchronization signal is generated based on the power supply synchronization clock signal, but it has the drawback that dot interference appears in the video during the video period.
In the present invention, the power supply synchronization similar to the conventional one is maintained in the vertical blanking period, while the dot interference is reduced in the vertical scanning period due to the highly stable clock signal reference which is asynchronous with the power supply. By reducing the image dot interference, it is possible to improve the image quality of the power supply synchronization type video camera.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts showing an embodiment of a video camera device according to the present invention.

FIG. 2 is a correlation diagram of a first clock signal and a second clock signal in one vertical cycle (1V).

[Explanation of symbols]

 1 sync signal generator 1a vertical sync signal generator 1b horizontal sync signal generator 2 phase comparator 3 voltage controlled oscillator circuit (VCO) 4 crystal oscillator circuit 5 switching circuit 6 vertical blanking period detection unit 7 switching control unit

Claims (5)

[Claims] 1. A first clock signal generating means for generating a first clock signal of a required frequency, which is controlled so as to be synchronized with an AC power supply of a commercial frequency, and a second clock signal of a frequency substantially the same as the clock signal. Second clock signal generating means for generating a clock signal asynchronously with the AC power source, a switching circuit for switching between the first clock signal and the second clock signal, and the first clock signal during the vertical blanking period. Based on the clock signal selected by the switching circuit, selecting a clock signal and generating a switching control signal for switching the switching circuit so as to select the second clock signal in the vertical scanning period. A video camera device comprising: a sync signal generating means for generating each of a vertical sync signal and a horizontal sync signal. 2. A phase comparison unit that compares the phase of a vertical synchronization signal with a power supply synchronization pulse signal generated based on the AC power supply, and outputs an oscillation control signal based on the comparison in the first clock signal generation means. And a voltage-controlled oscillation circuit that generates the first clock signal under the control of an oscillation control signal from the phase comparison unit.
The described video camera device. 3. The video camera device according to claim 1, wherein the second clock signal generating means is composed of a crystal oscillation circuit. 4. A vertical blanking period detection unit for detecting a vertical blanking period based on a vertical synchronization signal, and the switching control signal generating unit based on the detection by the vertical blanking period detection unit. 2. The video camera device according to claim 1, wherein the video camera device comprises a switching control unit that generates the switching signal and switches the switching circuit by the control signal. 5. The synchronizing signal generating means is composed of a vertical synchronizing signal generating section and a horizontal synchronizing signal generating section that generate a vertical synchronizing signal and a horizontal synchronizing signal by dividing the frequency of the clock signal from the switching circuit. The video camera device according to claim 1, wherein the video camera device is provided.