JPS63234776A - External phase locked loop circuit for television camera - Google Patents

Abstract

PURPOSE:To prevent the flow of a picture reflected on a monitor equipment and so on even when plural TV cameras are switched by separately eliminating a horuzontal synchronous signal and an equivalent pulse and so on included in the video of the plural TV cameras and obtaining an internal synchronous signal which is stable and synchronized with an external signal. CONSTITUTION:When the external synchronous signal from the other TV camera is inputted, the horizontal synchronizing signal and the equivalent pulse from the isolation circuit 1 of a synchronous circuit is compared with the internal synchronous signal of the camera outputted from a synchronous signal generator 6 by a phase comparator 5. The horizontal synchronizing signal outputted by the comparator 5 is turned on by a switch circuit 7 based on a timing from the generator 6 and is subjected to sample-and-hold. By this sampling, the equivalent pulse recept the timing of the horizontal synchronous signal in the equivalent pulse separated by the circuit 1 is eliminated. Besides, the sampled signal is supplied to a VCO circuit 9 through an LPF circuit 8 and by this output, the generator 6 is controlled and the synchronous signal (b) synchronized with the external video signal (a) is outputted.

Description

[Detailed description of the invention] [Industrial field of application] This invention is applicable to CG TV (C1
The present invention relates to camera control, and more specifically to an external synchronization circuit for a television camera that synchronizes an internal synchronization signal with an external synchronization signal of a CCTV camera.

[Conventional Example] Conventionally, in a CCTV system, for example, a video signal received by a camera is recorded field by field using a time-lapse VTR. However, when video signals from a plurality of cameras are switched and displayed on the screen of a monitor device as appropriate, both sides of the monitor device are streamed. The same thing happens when you play back the recorded screen. This screen flow can be eliminated by matching the phases of the synchronization signals between the cameras. For this reason, this type of camera uses an externally synchronized type of camera, and this externally synchronized type of television camera uses, for example, as shown in Figure 3, a horizontal A synchronization separation circuit 1 separates the equivalent pulses of the synchronization signal and the blanking period, an equivalent pulse removal circuit 2 removes equivalent pulses other than the interval of the horizontal synchronization signal, and the equivalent pulse removal circuit 2 adjusts the shifted phase. a phase adjustment circuit 3, a phase comparator 5 that detects a phase shift between the phase-adjusted horizontal synchronization signal and equivalent pulse and a synchronization signal from a synchronization signal generator 4 of the television camera; Voltage controlled oscillator (V CO: Volt) whose frequency is controlled
age-Controlled 0scillator
) circuit 6, etc., and the synchronizing signal generator 4 outputs a synchronizing signal having the same phase as the external horizontal synchronizing signal. That is, as shown in FIG. 4(a), the horizontal synchronization signal and equivalent pulse of the video signal from another television camera are obtained by the synchronization separation circuit 1.

This horizontal synchronizing signal and the equivalent pulse are generated with a constant width τ
, is converted into a pulse of . At this time.

With this pulse width, by reducing the interval between the horizontal synchronizing signals to approximately three-fourths as shown in FIG.

The phase of the horizontal synchronizing signal and the signal corresponding to the equivalent pulse outputted from the equivalent pulse removal circuit 2 is changed into a pulse with a predetermined width τ2 by a mono multi-circuit or the like provided in the phase adjustment circuit 3, thereby performing phase adjustment. . The phase-adjusted horizontal synchronization signal and the signal synchronized with the equivalent pulse are detected by the phase comparator 5. A signal of a predetermined level voltage is output from the vCo circuit 6 according to the phase difference, and a synchronization signal is generated based on this signal. The generator 4 outputs an external synchronization signal.

[Problems to be Solved by the Invention] By the way, the equivalent pulse removal circuit 2 and the phase adjustment circuit 3 in the external synchronization circuit are constructed of monomulti circuits. The pulse width output by this monomulti circuit is determined by the values of the resistor and capacitor. The values of these resistors and capacitors change with changes in temperature and the like. In response to this change, the pulse width output from the mono multi-circuit changes, making it impossible to achieve the purpose of the single-phase adjustment circuit 3, and the external synchronization circuit may no longer output a synchronization signal whose phase has been accurately adjusted. Ta.

That is, in such an external synchronization circuit, when a plurality of cameras are switched as in a CCTV system, there is a problem that the initial phase adjustment setting is shifted due to temperature change.

This invention was made in view of the above problems, and its purpose is to obtain a synchronization signal that is unaffected by temperature changes, etc., and to prevent the shift of the video screen that occurs when switching between multiple cameras. The object of the present invention is to provide an external synchronization circuit that enables the following.

[Means for Solving the Problems] In order to achieve the above object, the present invention synchronizes a plurality of television cameras when they are appropriately switched and video signals from the television cameras are displayed on a monitor device. In the external synchronization circuit of a television camera, there is a synchronization separation circuit that separates the horizontal synchronization signal, equivalent pulse, etc. contained therein from the video signal of another television camera, and the horizontal synchronization signal, equivalent pulse, etc. and the television. a phase comparator that compares the phase with an internal synchronization signal of the camera; a sampling and hold circuit that samples and holds the signal output from the phase comparator at the timing of the horizontal synchronization signal; The device includes a voltage controlled oscillator that outputs a signal with a voltage level corresponding to the signal, and a synchronization signal generator that outputs a synchronization signal synchronized with the external video signal based on the voltage level.

[Example] Hereinafter, an embodiment of the present invention will be described based on FIG. 1.

In addition, in the figure, the same parts as in FIG. 3 are given the same reference numerals, and redundant explanation will be omitted.

In the figure, a phase comparator 5 compares the horizontal synchronization signal and equivalent pulse output from the synchronization separation circuit 1 with the internal synchronization signal of the camera output from the synchronization signal generator 6. The signal resulting from this comparison is held by a switch circuit (for example, an analog switch) 7 being turned on at the timing of a horizontal synchronizing signal (HD) output from the synchronizing signal generator 6.

That is, the comparison result is sampled at the timing of the horizontal synchronization signal from the synchronization signal generator 6, so that among the equivalent pulses separated by the synchronization separation circuit 1, equivalent pulses other than the timing of the horizontal synchronization signal are removed. . Also,
The sampled signal is L P F (Low Pa
The signal is input to the 700 circuit 9 via the 5s filter circuit 8. Then, the 700 circuit 9 outputs a signal with a voltage level corresponding to the comparison result, and this signal is input to the synchronization signal generator 6. As a result, the synchronization signal generator 6 outputs a synchronization signal that is synchronized with the horizontal synchronization signal of the external video signal.

Next, the operation of the external synchronization circuit having the above configuration will be explained based on the time chart shown in FIG.

First, when a video signal from another television camera is input, the synchronization separation circuit 1 outputs the horizontal synchronization signal, equivalent pulse, etc. of the video signal shown in FIG. This horizontal synchronizing signal and equivalent pulse are the same as the conventional one. Then, the horizontal synchronization signal, equivalent pulse, and internal synchronization signal of the camera output from the synchronization signal generator 6 (see Fig.
(shown in b)) are compared by the phase comparator 5. Then, the phase comparator 5 outputs a signal of a predetermined voltage according to the phase difference of the input signals. For example, if the phase difference is large, this is a high level voltage signal, and if the phase difference is small, this is a low level voltage signal. This signal is the horizontal synchronization signal (
Sampling and holding are performed at the timing shown in (c) of the figure. The held predetermined level voltage signal is L
The PF circuit 8 removes noise and the like. As a result, the 700 circuit 9 outputs a voltage signal according to the phase difference. Then, the phase comparator 5, the synchronizing signal generator 6, and the VCO circuit 9 perform P L
ock Loop) is formed, and the synchronization signal generator 6 generates a synchronization signal (pulse width τ shown in FIG. ) is output.

Therefore, unlike the external synchronization circuit shown in FIG. 3, there is no need to use a mono-multi circuit, so a signal synchronized with the external synchronization signal can be obtained without being affected by temperature changes. Therefore, by using the synchronization circuit having the above-mentioned circuit configuration in the television cameras of the CCTV system, the screens of images received by those cameras will not shift when the cameras are switched.

[Effects of the Invention] As explained above, according to the present invention, in a CCTV system, etc., the horizontal synchronization signal and equivalent pulse of an external video signal from another television camera are output from the synchronization signal generation circuit of the television camera. A comparator that directly compares the internal synchronization signal of the camera, a circuit that samples and holds the phase difference detected by the comparator using an external horizontal synchronization signal, and a circuit that controls the level voltage according to the sampled phase difference. Since the circuit configuration is equivalent to a PLL with 700 circuits that output signals, equivalent pulses other than the horizontal synchronization signal interval are removed from the input equivalent pulses, and synchronization with external signals is performed without being affected by temperature changes. A stable internal synchronization signal can be obtained.

Therefore, even when switching between a plurality of television cameras, there is an effect that both sides displayed on a monitor device etc. do not change.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an external synchronization circuit for a television showing an embodiment of the present invention, FIG. 2 is a time chart diagram explaining the operation of the external synchronization circuit, and FIG. 3 is a conventional external synchronization circuit for a television. A block diagram of the circuit, FIG. 4 is a time chart diagram illustrating the operation of the conventional external synchronization [J path. In the figure, 1 is a synchronous separation circuit, 5 is a phase comparator, 6 is a synchronous signal generator, 7 is a switch circuit, 8 is an LPF circuit, and 9 is a V
This is a CO circuit.

Claims (1)

[Claims] When a plurality of television cameras are appropriately switched and the video signals of the television cameras are displayed on a monitor device, an external synchronization circuit of the television camera that synchronizes the video signals of the other television cameras is provided. A synchronization separation circuit that separates a horizontal synchronization signal, equivalent pulses, etc. contained therein from a video signal, and a phase comparator that compares the phase of the horizontal synchronization signal, equivalent pulses, etc. with an internal synchronization signal of the television camera. , a sampling and holding circuit that samples and holds the signal output from the phase comparator at the timing of the horizontal synchronization signal, and a voltage controlled oscillator that outputs a signal with a voltage level corresponding to the sampled and held signal. An external synchronization circuit for a television camera, comprising: a synchronization signal generator that outputs a synchronization signal synchronized with the external video signal based on the voltage level.