JPS5955647A - Agc system for optical communication - Google Patents

Abstract

PURPOSE:To reduce the error of an AGC operation and to improve the quality of a received picture, by superposing a pilot signal only to a synchronizing signal having a fixed level on DC. CONSTITUTION:When an output (a) is obtained from a TV camera 1, a synchronizing signal extracting part 2 extracts a synchronizing signal out of the output (a). A switching part 4 outputs a pilot signal (c) to a superposing part 5 on the basis of the detection signal (b) and the superposing part 5 superposes the output (c) to the output (a) and applies the superposed signal to an optical transmitter 6. The transmitter 6 feeds the received signal as an optical signal. A photodetector 8 receives the optical signal transmitted through an optical fiber 7, converts the received signal into an electric signal again, then outputs the electric signal to an AGC amplifier 11. The amplified signal is inputted to a pilot signal extracting part 9. The extracting part 9 extracts only the pilot signal component out of the transmission signal and applies the extracted signal to an AGC input generating part 10. The generating part 10 generates an AGC input and applies the input to the amplifier 11. On the basis of the control input, the amplifier 11 executes the gain control of a video signal, and supplies the controlled signal to a monitor device 12.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an AGC (automatic gain control) system for optical communication;
In particular, AGC using pilot signals In recent years, optical communications using optical fibers as transmission paths have been adopted in ITV systems and the like.

In such an ITV system, the video signal attenuates or fluctuates due to transmission loss or fluctuations in transmission loss, so if the received video signal is reproduced as a received image on a monitor device without gain, the received image will have a contrast difference. The ratio will deteriorate and become difficult to see.

Conventionally, in order to prevent such deterioration of the received image, an AGC method (hereinafter referred to as pilot AGC) using a pilot signal has been used.
It is called a method. ) has been adopted. This pilot AQ
In the C method, a pilot signal is always inserted in a frequency band different from that of the video signal on the transmitting side5, and gain control is performed on the received video signal on the receiving side based on the pilot signal of this side band. . However, if this pylon AGC method is adopted for optical communication, LE for optical communication
Since the linearity of optical communication elements such as D is poor, the pilot signal is modulated by the video signal, causing an error in the AGC operation and deteriorating the received image.

In short, the LED for optical communication has the characteristics as shown in FIG. 1, and the light emission output is approximately proportional to the complimentary current, but the linearity is not very good. In the figure, when a pilot signal of amplitude i' pil is uniformly inserted into the input signal as shown in A,
The amplitude of the pilot signal component at the light emission output differs in each part as shown by B in the figure. Therefore, the pilot signal component in the light emission output varies depending on the input signal, causing an error in the AGC operation as described above, and deteriorating the received image. In order to solve this problem, it is conceivable to provide a distortion correction circuit that corrects the non-linear distortion of the optical communication LED as described above. This distortion correction circuit is essentially a predistortion adding circuit, but since this non-direct a distortion varies depending on the frequency, it is possible to compensate for the distortion of the video signal, but it is not possible to compensate for the distortion of the pilot signal. It was impossible.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and is intended to reduce errors in AGC operation and improve the quality of received images.
The purpose is to provide a GC method.

[Summary of the invention]

Therefore, the present invention utilizes the fact that the synchronization signal is at a constant DC level, and uses the fact that the synchronization signal is a pilot signal only for this synchronization signal.
: The above objective was achieved by superimposing.

[Embodiments of the invention]

The present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing signal waveforms at each part thereof.

In Fig. 2, l is a television camera, 2 is a synchronization signal extraction section, 3 is a pilot signal generation section, 4 is a switch section, 5 is a superimposition section, 6 is an optical transmitter, 7 is an optical fiber, and 8 is an optical receiver. 9 is a pilot signal extraction section, 10 is an AGC control control input section generating section 1 is an AGC amplifier, and 12 is a monitor device.

The television camera 1 obtains a subject image as a video signal, and forms and transmits a signal train in which a synchronization signal T and a video signal P are alternately continuous.

The synchronization signal extracting section 2 extracts the synchronization signal T of the output a of the television camera 1, and the switch section 4&''i
It is closed based on the output (synchronization signal detection signal) b of the synchronization signal extraction section 2 and allows the pilot signal output from the pilot signal generation section 3 to pass only during the synchronization signal period.

The superimposing section 5 superimposes the signal C obtained from the switch section 4 on the output a of the television camera 1, and the optical transmitter 6 uses the output d of the superimposing section 5 as a transmission signal (electrical signal). This transmission signal is converted into an optical signal by an optical communication LED or the like, and is transmitted via the optical fiber 7. The optical receiver 8 converts the optical signal transmitted via the optical fiber 7 into a transmission signal (electrical signal) again, and the pilot signal extraction unit 9 converts the output of the optical receiver 8 via the AGC amplifier 11 (transmission signal) by using a bandpass filter to extract only the pilot signal component. AGC control control input unit 10 detects this extracted pilot signal component, compensates for the period (video signal period) in which no pilot signal is superimposed using a peak hold circuit, etc., and outputs the AGC signal to the AGC booster 11. It provides control input.

Next, the operation of this embodiment will be explained. First, when the output a is obtained from the television camera 1, the synchronization signal extraction section 2 extracts the synchronization signal T from this output a, and outputs the synchronization signal detection signal. Output. Based on this signal, the switch section 4 outputs a pilot signal to the superimposition section 5 only during the synchronization signal period,
The superimposing unit 5 combines this output C and the output a of the television camera 1.
and the transmission signal d is given to the optical transmitter 6. The optical transmitter 6 sends out this transmission signal as an optical signal suitable for the optical fiber 7. The optical signal transmitted through the optical fiber 7 is received by the optical receiver 8, converted back into a transmission signal (electrical signal), and then input to the AGC amplifier 11.

Thereafter, the amplified signal is input to the pilot signal extraction section 9. The pilot signal extraction unit 9 extracts only the pilot signal component within the synchronization signal period in this transmission signal,
The AGC control input generating section 10 generates an AGC control input based on the input of the AGC control input generating section 10 and supplies it to the AGC amplifier 11 . AGC amplifier 11
performs gain control of the input video signal based on this control input, and the video signal whose gain has been controlled in this manner is input to the monitor device 12 and is received.

Therefore, in this embodiment, the pilot signal is superimposed only on the synchronization signal, which is at a constant DC level, so that it is not modulated by the video signal, does not cause errors in AGC operation, and obtains a high-quality received image. be able to.

Incidentally, if the synchronization signal period of the AGC control control input generating section 10 is constant, a simple average YAGC control input of the detected output of the pilot signal component may be used.

〔Effect of the invention〕

As explained above, according to the present invention, by superimposing the pilot signal only on the synchronization signal, fluctuations in the pilot signal due to fluctuations in the video signal are prevented, errors in AGC operation are reduced, and high-quality received images are obtained. can be obtained.

[Brief explanation of drawings]

FIG. 1 is a current-emission output characteristic diagram of an LED for optical communication, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing signal waveforms of each part thereof. 1...Television camera, 2...Synchronization signal extraction section, 3...Pilot signal generation section, 4 e a
a an switch unit, 5... superimposing unit, 6... optical transmitter, 7... optical fiber, 8... optical receiver,
9...Fist/pilot signal extraction section% 10...@AG
C control input generation section, 11...-AGC amplifier, 12.
...Monitor device. yoke

Claims (1)

[Claims] A transmitter includes a signal forming means for forming a signal train consisting of a synchronization signal and a video signal that are alternately continuous, and a pilot signal for superimposing a pilot signal on the synchronization signal of the formed signal train and transmitting the resultant signal as a transmission signal. A superimposing means and a transmitting means for converting the transmitted transmission signal into an optical signal and transmitting it to the optical transmission line are provided, and the optical signal transmitted via the optical transmission line is sent to the receiving device again as the transmission signal. a pilot signal extracting means for extracting the pilot signal superimposed on the synchronization signal of the converted transmission signal; and a means for controlling the gain of the video signal based on the extracted pilot signal. An AGC system for optical communication characterized by the provision of.