JP2877683B2 - External synchronization method of video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synchronizing a plurality of color television cameras.

[0002]

2. Description of the Related Art Today, images taken by a plurality of television cameras are often monitored by a single monitor television, and when images of a plurality of cameras are switched and viewed by a single monitor television as described above, Synchronization between the synchronization signals of the television cameras is performed so that the image on the monitor is not disturbed at the time of switching.

In a large-scale facility, the same synchronization signal is sent from a single synchronization signal generator to each television camera. However, in a surveillance camera device and the like, the frequency of a 60 Hz commercial power supply is reduced. The power supply synchronization method for controlling the reference frequency signal so that the frequency and timing of the vertical synchronization signal are adjusted to the commercial power supply as the reference frequency is often used because it is simple.

In the power supply synchronization method based on the commercial power supply, oscillation control by a PLL method is often used. As shown in FIG. 2, an oscillation circuit 15 in a television camera forms a reference frequency signal of, for example, about 14 MHz. Then, this reference frequency signal is frequency-divided by a frequency dividing circuit 17 to obtain a horizontal synchronizing signal or a horizontal synchronizing timing signal of about 15.7 kHz.
The reference frequency signal is divided by the frequency dividing circuit 18 to form a 60 Hz vertical synchronizing signal or a vertical synchronizing timing signal. The 60 Hz phase reference signal is supplied from the power supply line 11 of the commercial power supply by the zero cross detecting circuit 12. The phase difference is detected by comparing the phase reference signal with the vertical synchronizing signal by the phase comparison circuit 13, and the loop filter 14
The timing of the vertical synchronizing signal is adjusted to the commercial power supply by controlling the oscillation circuit 15 through the interface, and synchronization between the synchronizing signals of all the television cameras using the same commercial power supply is performed.

[0005]

As described above, the PLL
When the oscillation circuit is controlled so that the vertical synchronizing signal is 60 Hz by the method and the reference frequency signal is output from the transmitting circuit, the horizontal synchronizing signal becomes 15.75 kHz, and the frequencies of the vertical synchronizing signal and the horizontal synchronizing signal become is also the allowable range, 59.94 Hz vertical synchronization frequency is normalized by NT SC method, the horizontal synchronizing frequency 15.73
The reference is 4 kHz, and the color subcarrier of the color video signal is 3.579545 MHz.
The permissible error range of the chrominance subcarrier is 10 Hz.

As described above, the permissible range of the chrominance subcarrier is extremely strict with respect to the permissible range of the vertical synchronization and the horizontal synchronization, and the frequency of the reference frequency signal adjusted so that the vertical synchronization signal is 60 Hz is divided. When the color subcarrier is formed, 3.
Since it becomes 58,125 MHz and cannot be used because an error of 3580 Hz occurs, in a power-synchronous color television camera, only a color subcarrier is formed as an asynchronous type using another oscillation circuit, and the cycle of the color subcarrier is used. And the period of the horizontal synchronizing signal deviate from each other, a dot-shaped image defect may appear on the screen of the monitor TV, and when the TV camera is switched, the color displayed on the monitor TV changes and the color shift occurs. Sometimes it did.

[0007] This power cycle method can be used in an area where a commercial power supply of 60 Hz is used.
The system cannot be adopted in the commercial power region of Hertz, and a system for transmitting a synchronization reference signal to each television camera is required.

[0008]

According to the present invention, a 60 kHz sub-phase reference signal is formed by a PLL system based on a commercial power supply, and this sub-phase reference signal is counted 1001 times.
The signal divided by the data and the divided signal and the vertical synchronization signal
A reference frequency signal is formed by controlling the oscillation circuit using a PLL method for comparing the reference frequency signal with the reference signal, and the reference frequency signal is frequency-divided to form a color subcarrier, a horizontal synchronizing signal, and a vertical synchronizing signal.

[0009]

According to the present invention, since the sub-phase reference signal of 60 kHz is formed by the PLL method on the basis of the commercial power supply, the cycle of the sub-phase reference signal can be set to the timing corresponding to the cycle of the commercial power supply. Further, since the oscillation circuit is controlled by the PLL method using the sub-phase reference signal, the synchronization of the reference frequency signal output from the oscillation circuit can be set to the timing based on the synchronization of the commercial power supply. The frequency of the reference frequency signal can be easily changed depending on the frequency.

Further, since the sub-phase reference signal is set to 60 kHz and the sub-phase reference signal is frequency-divided 1001 times by a counter and compared with the vertical synchronizing signal, if the frequency of the reference frequency signal is controlled, Frequency of 59.94
Hertz, and a vertical synchronization frequency based on the NTSC standard can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a periodic signal forming circuit of a color television camera according to the present invention includes a zero-cross detecting circuit 12 connected to a power line 11, a sub-phase reference signal generating circuit 20, a synchronizing signal generating circuit. The sub-phase reference signal generation circuit 20 includes one phase comparison circuit 23, a loop filter 24, a frequency divider circuit 27, and an oscillation circuit 25. The synchronization signal generation circuit 30 includes four synchronization signal generation circuits. Dividing circuit 3
1, 41, 43, and 45, and one phase comparison circuit 33, a loop filter 34, and an oscillation circuit 35.

The sub-phase reference signal generation circuit 20 outputs a 60-kHz sub-phase reference signal to the synchronization signal generation circuit 30 by using a 60-kHz oscillation circuit for the first oscillation circuit 25 as the oscillation circuit. This sub phase reference signal is converted into a first frequency divider 27 of the sub phase reference signal generation circuit 20.
Is also entered.

In this embodiment, the first frequency dividing circuit 27 has
000 times counter, and the first frequency dividing circuit 27
Divides the sub phase reference signal to form a signal of 60 Hz, and inputs the signal to the first phase comparison circuit 23 of the sub phase reference signal generation circuit 20. The phase reference signal from the detection circuit 12 is also input.

In the first phase comparison circuit 23, the phase reference signal from the zero-cross detection circuit 12 and the first oscillation circuit 2
5 outputs a signal based on the phase difference from the signal obtained by frequency-dividing the sub-phase reference signal from the first frequency divider 27 by the first frequency divider 27, and returns this output signal to the first oscillation circuit 25 via the first loop filter 24. As a result, the sub-phase reference signal generation circuit 20 generates a signal at a constant timing based on the 60 Hz phase reference signal.
It forms a kilohertz sub-phase reference signal.

Therefore, the sub-phase reference signal generating circuit 20
Is for forming a sub-phase reference signal of 60 kHz by a PLL method using a commercial power supply. Then, in the synchronizing signal generation circuit 30, 1
A reference frequency signal is output using an oscillation circuit of 4.31818 MHz, and this reference frequency signal is frequency-divided by a third frequency dividing circuit 41 to form a color subcarrier, and a fourth frequency dividing circuit 43 The horizontal synchronization signal or the horizontal synchronization timing signal is formed by dividing the frequency by 1/910 with
The frequency is divided by 238875 by 1/55 to form a vertical synchronizing signal or a vertical synchronizing timing signal. The color subcarrier, the horizontal synchronizing signal and the vertical synchronizing signal are output to the camera circuit, and the vertical synchronizing signal is converted into a synchronizing signal. The signal is input to a second phase comparison circuit 33 in the generation circuit 30. A 1001 times counter is used as the second frequency division circuit 31. The second frequency division circuit 31 converts the sub-phase reference signal to 1001 times.
The frequency-divided signal is also input to the second phase comparison circuit 33.

Accordingly, the second phase comparison circuit 33 receives the vertical synchronization phase reference signal of 59.940005994 Hz obtained by dividing the sub-phase reference signal from the second frequency division circuit 31, and outputs the vertical synchronization phase reference signal and the vertical synchronization phase reference signal. The phase difference from the vertical synchronization signal from the fifth frequency dividing circuit 45 is detected, and an output signal based on this detection is returned to the second oscillation circuit 35 via the second loop filter 34, and the oscillation frequency of the second oscillation circuit 35 To 14.
The frequency is controlled to 31818 megahertz, and the synchronization signal generating circuit 30 forms a reference frequency signal based on the sub-phase reference signal by a PLL method.

[0017] Thus, the vertical synchronizing signal is outputted from the fifth frequency divider 45 becomes 59.94 Hz, the horizontal synchronizing signal output from the fourth frequency divider 43 as 15.734265 kg hertz, color subcarrier Is output from the third frequency dividing circuit 41 as 3.579454 MHz, and all of the color subcarriers, the horizontal synchronization signal and the vertical synchronization signal satisfy the NTSC standard, and are formed in synchronization with the cycle of the commercial power supply. be able to.

In this embodiment, a sub-phase reference signal of 60 kilohertz is formed by the sub-phase reference signal generating circuit 20 by the PLL method based on the commercial power supply as described above, and the sub-phase reference signal is divided and vertically synchronized. Since the phase reference signal is formed, an accurate vertical synchronization frequency of the NTSC standard can be obtained. Since the reference frequency signal is formed by the PLL method based on the vertical synchronization phase reference signal, the reference frequency signal is separated. The circulated color subcarrier can also meet the NTSC standard, the oscillation circuit for the vertical synchronization signal and the horizontal synchronization signal can be shared as the oscillation circuit for the color subcarrier, and the color subcarrier can be synchronized with the cycle of the horizontal synchronization signal. Because it can be an image signal that does not cause dot interference on the screen, and because vertical synchronization is synchronized with commercial power supply,
By performing the timing of resetting the second frequency divider circuit 31 using the phase reference signal in each TV camera, the vertical synchronization of all the TV cameras using the same power supply can be easily matched. is there.

In this embodiment, the first frequency dividing circuit 27 uses a counter 1000 times. However, if the sub-phase reference signal is frequency-divided using a 1200-times counter, the sub-phase reference signal is set to 60 kHz. Therefore, the first phase comparison circuit 2
The frequency of the signal input to 3 can be set to 50 Hz, so that it can be used even in an area where the commercial power supply frequency is 50 Hz.

In the above embodiment, the sub-phase reference signal is set to 60
The second frequency dividing circuit 31 uses a counter that can divide the frequency by a factor of 1001, and the first frequency dividing circuit 27 uses a counter that divides the frequency by a factor of 1/1000 or 1200. Although it is intended to be used in the 50 Hz region, the frequency of the sub-phase reference signal is made higher, and the division ratios of the first frequency divider 27 and the second frequency divider 31 are appropriately selected to provide a more accurate color subcarrier. And a synchronization signal, and it is also possible to form the frequency of the synchronization signal in accordance with not only the NTSC standard but also other standards.

[0021]

According to the present invention, a PLL based on a commercial power supply is used.
Form a 60 kHz sub-phase reference signal,
Since the oscillation circuit is controlled by dividing the sub-phase reference signal and using the PLL method again, the reference frequency signal output from the oscillation circuit can be synchronized with the commercial power supply.

Since a vertical synchronizing signal, a horizontal synchronizing signal, and a chrominance subcarrier are formed based on the reference frequency signal,
The phase of the horizontal synchronizing signal and the phase of the chrominance subcarrier can be matched to prevent an image disturbance due to the chrominance subcarrier. Further, since the synchronizing signal is formed based on the commercial power supply, synchronization between the television cameras using the same commercial power supply can be easily performed.

Further, since the method of dividing the sub-phase reference signal and detecting the phase difference from the commercial power is used, the frequency of the commercial power can be easily adjusted not only in the region of 60 Hz but also in the region of 50 Hz. It is a method that can be implemented .

[Brief description of the drawings]

FIG. 1 is a circuit block diagram for implementing a method according to the present invention.

FIG. 2 is a circuit block diagram showing a conventional PLL power supply synchronization method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Power supply line 12 Zero crossing detection circuit 13 Phase comparison circuit 14 Loop filter 15 Oscillation circuit 17, 18 frequency dividing circuit 20 Sub-phase reference signal generation circuit 23 1st phase comparison circuit 24 1st loop filter 25 1st oscillation circuit 27 1st division Frequency dividing circuit 30 Synchronous signal generating circuit 31 Second frequency dividing circuit 33 Second phase comparing circuit 34 Second loop filter 35 Second oscillating circuit 41 Third frequency dividing circuit 43 Fourth frequency dividing circuit 45 Fifth frequency dividing circuit

Claims (1)

(57) [Claims] 1. A PLL system based on a commercial power supply
Generate 60 kHz sub-phase reference signal as sub-phase reference signal
Circuit, and this sub-phase reference signal is used as a synchronization signal generation circuit.
And the signal divided by the counter 1001 times
14.318 by PLL method comparing with direct synchronization signal
A method of externally synchronizing a video camera, comprising: forming a megahertz reference frequency signal; and dividing the reference frequency signal to form a color subcarrier, a horizontal synchronization signal, and a vertical synchronization signal.