JPH01284076A - Synchronizing signal transmission system for television camera - Google Patents

Abstract

PURPOSE:To attain narrow band transmission and to facilitate file design by using a clock signal whose frequency is twice the frequency of a horizontal synchronizing signal and whose duty ratio is 50% and applying frequency multiplex to the synchronizing signal obtained from the said clock signal through phase modulation by a vertical synchronizing signal and transmitting the result. CONSTITUTION:In order to match the phase of a horizontal synchronizing signal (HD) at a camera control section (CCU) and the phase of the signal HD returned from a camera head section, a phase comparator 8 compares the phases of both the signals HD. An error caused as the result of comparison is inputted to a voltage controlled oscillation circuit 7 and the oscillated frequency is controlled to apply phase matching. In this case, the voltage controlled oscillator whose duty ratio is always 50% is used for the oscillated output. The output pulse is oscillated by a frequency being twice the frequency of the horizontal synchronizing signal HD and it is used as a clock and a vertical synchronizing signal (VD) is used to apply PSK by a phase modulation (PSK) circuit 2. The pulse subject to PSK is modulated by a modulation circuit 3 to apply frequency multiplex to plural other signals and the result is sent through a transmission line 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of transmitting a synchronization signal for a television camera.

[Conventional technology]

A television camera includes a camera head section and a camera control section (hereinafter abbreviated as CCU).

There are things that are separate. In this case, the camera head captures an image of the subject and converts the intermediate signal into an electrical signal. The signal converted to an electrical signal is called a video signal. This video signal is transmitted to the CCU side, passes through various process circuits, and is converted into a standard television signal. At this time, in large broadcast cameras, in addition to the three primary color signals of red, green, and blue, one other control signal is sent from the camera head to the CCU.
fart.

Alternatively, it is transmitted from the CCU to the camera head section.

For this reason, a thick multi-core camera cable is required.
A system has come to be used in which these signals are zero-frequency multiplexed and transmitted over a single coaxial cable. A characteristic of coaxial cables is that as the cable length increases, the amount of attenuation of high frequency component signals increases, so
A problem arises in that the transmission frequency band cannot be set high.

In addition, the video signal is based on a television system (for example, NTSC).
, PAL, SECAM), but generally requires a band of several MHz, so when modulated (
This is because the spread of the sidebands (same for both frequency modulation and amplitude modulation) is determined by this band.

It is impossible to narrow the band. , 1. Conventionally, a composite synchronization signal consisting of a horizontal synchronization signal and a vertical synchronization signal was transmitted as the synchronization signal. This synchronization signal is C
This is to synchronize the camera head from the CU side.
This is a pulse signal with a narrow pulse width so that it can be processed within the blanking period of the video signal.

As shown in Figure 2, the spread of one frequency spectrum is
Inversely proportional to pulse width. For this reason, the sideband after modulation also becomes wider, and the frequency allocation of the synchronization signal also increases from 2 to 2.
Conventionally, a band of 3 MHz was required.

As mentioned above, when the cable length is increased, the attenuation at high frequencies is large, so if the transmission frequency is set to a high frequency, the S/N will deteriorate. Also, the video signal band cannot be narrowed, so if you reduce the synchronization signal band,
Jitter between synchronization signals increases.

In addition, in order to keep the maximum usable frequency as low as possible, there was a problem that it became quite difficult to design a filter that separates two frequencies.

[Problem to be solved by the invention]

The above-mentioned conventional technology has the disadvantage that the occupied band becomes wide because the composite synchronization signal is directly modulated and transmitted.

The present invention aims to eliminate these drawbacks and enable narrowband transmission.

[Means to solve the problem]

In order to achieve the above object, the present invention sets the duty ratio of the synchronizing signal to 50%. Figure 1 is 0
FIG. 1 is a block diagram showing the overall configuration of the present invention. In the figure, the duty ratio of the horizontal synchronization signal (hereinafter abbreviated as HD) is 5.
0%, the HD is shaped through the waveform shaping circuit 1. The q-shaped waveform is used as a clock in the 1-phase modulation circuit, and this clock is phase modulated (hereinafter referred to as PSK) using a vertical synchronization signal (hereinafter referred to as VD). omitted)'-fru. In order to transmit the PSK signal from the CCU side to the camera head side, it is modulated by the modulation circuit 3. The modulated signal passes through a transmission path 4 and is demodulated by a demodulation circuit 4 on the camera head side.

A clock is regenerated by the PSK demodulation circuit 5, and VD is separated using the clock.

[Effect]

As a result, the frequency spectrum band of the synchronization signal? Narrow (
As a result, it has become possible to narrow the occupied band after modulating the synchronization signal.

〔Example〕

An embodiment of this invention will be described below.

In a television camera that performs interlaced scanning, the HD and VD cycles are as follows.

The second VD matches the phase with the HD. Therefore, in this interlaced scanning method.

HD cannot be used as is for PSK clock.

Therefore, a signal with twice the frequency of HD is used as a lock, and the frequency is divided by 172 on the camera head side.

Use as HD. Furthermore, as the length of the transmission cable becomes longer, a phase difference occurs between the CCU side and the camera head side, so generally phase leading HD is sent to the camera head side. Here, on the CCU side.

By comparing the phase of the synchronization signal sent back from the camera head side and the synchronization signal from the CCU side so that the phase of the signal sent from the camera head side matches, the circuit structure always matches the phase even if the cable length is different. It becomes. Here, as shown in FIG. 2, the relationship between the pulse width and the frequency spectrum is as follows, assuming that the repetition frequency is f+, the repetition period is il, and the pulse width is t2.

As can be seen from the figure, the pulse width 2 is small (9
The frequency f2 of the generated sideband becomes thicker.

In other words, it means expanding the frequency spectrum by one frequency.

The frequency spectrum sequence at that time becomes the repetition frequency. From the above, it follows that a pulse train with a duty ratio of 50%, that is, a pulse width τ2 that is half of the repetition periodic element 1, has the narrowest energy spectrum spread. An embodiment of the present invention will be described below with reference to FIG.

HD on the CCU side and H sent back from the camera head side
In order to match the phase of D, the phase of both HDs is determined by the two-phase comparator 6. compare. The error resulting from the comparison is input to the voltage controlled oscillation circuit 7, and the oscillation frequency is controlled to achieve phase matching.

At this time, a voltage controlled oscillator whose duty ratio is always 50% is used for one oscillation output. Here, for the reason mentioned above, this output pulse is oscillated at twice the frequency of the horizontal synchronizing signal HD, and as a lock, PSK is performed in the PSK circuit 2 using VD. The PSK pulse is modulated by a modulation circuit 3, and a plurality of other signals (not shown) are frequency-multiplexed.

Transmission is performed using one transmission line 11. On the camera head side,
After separating unnecessary frequency signals from the transmitted frequency multiplexed signal using a separation circuit (not shown).

A demodulation circuit 4 demodulates a clock signal having twice the frequency of HD, and a PSK demodulation circuit 5 demodulates VD. The PSK demodulation circuit 5 restores the clock signal with twice the HD frequency, and
The frequency is halved by the frequency dividing circuit 8 and HD is reproduced. The reproduced HD is modulated by the modulation circuit 9 on the camera head side, and the C
It is transmitted to the CU side, the demodulation circuit 10 on the CCU side restores the HD, and the phase comparator 6 compares it with the HD on the CCU side. Generally, the HD signal sent back is multiplexed with the video signal sent from the camera head side to the CCU side. Since a sufficiently wide transmission band is secured for the video signal, the synchronization signal can sufficiently pass through, making it easy to reproduce.

〔Effect of the invention〕

According to the present invention, since the band of the synchronization signal transmitted from the CCU side to the camera head section can be narrowed, the transmission band of other video signals can be used effectively.

Moreover, it becomes possible to provide some leeway in the design of the filter.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is a block diagram showing the configuration of the present invention.
FIG. 3 is a diagram illustrating pulse width and frequency spectrum distribution, and is a block diagram illustrating an embodiment of the present invention.

Claims (1)

[Claims] 1. In a frequency multiplex transmission system that performs frequency multiplex transmission of signals between the head section of a television camera and a television camera control section, the duty ratio is 50% at twice the frequency of the horizontal synchronization signal.
A synchronization signal transmission method for a television camera, characterized in that a synchronization signal obtained by phase modulating the clock signal with a vertical synchronization signal is frequency-multiplexed and transmitted using a clock signal.