JPS6022815A - Agc system - Google Patents

Abstract

PURPOSE:To receive a burst signal without error by storing an output of an AGC circuit while digitizing it during the presence of an input and converting a stored content into an analog signal at the interruption of the input signal so as to control a gain variable amplifier. CONSTITUTION:While a digital signal is inputted, a signal interruption detecting circuit 9 controls a switch circuit 5 and applies an output of the AGC circuit to the gain variable amplifier 2 as a control signal and also digitizes the signal by an A/D converter 7 and stores it to a memory 8. When no digital signal is inputted, the signal interruption detecting circuit 9 controls the switch circuit 5 so as to apply the signal converted into analog signal from the stored content of the memory 8 by a D/A converter 6 to the gain variable amplifier 2. Thus, in transmitting the burst signal, the signal is received without error from the bit of the first input signal.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to an optical receiving system for digital signals having a variable gain amplifier and an AGC circuit that keeps the output level of the variable gain amplifier constant. This invention relates to an AGC method that can improve transmission efficiency when the signal is a burst signal.

(b) Prior art and problems Figure 1 is a block diagram of the main parts of a conventional optical receiving system, and Figure 2 is a time chart of each part of Figure 1 when a burst signal is input. B) shows the output amplitude of the variable gain amplifier, and (C) shows the gain of the variable gain amplifier.

In the figure, 1 is a light receiving element, 2 is a variable gain amplifier, 3 is an AGC circuit, and 4 is a discriminator.

In FIG. 1, a light modulated digital signal is converted into an electrical signal by a light receiving element 1, passes through a variable gain amplifier 2, is discriminated and reproduced by a discriminator 3, and is output. At this time, the AGC circuit 3 controls the output (i) amplitude of the variable gain amplifier 2 to be constant.

Therefore, when no digital signal is input, the gain of the variable gain amplifier 2 is the maximum value, 0. In this state, as shown in Figure 2 (5).
When the burst signal shown in Figure 2 is input, the following problem occurs.

The response speed of the AGC circuit 3 is set to a speed considerably lower than the transmission speed of digital No. 43 for stability. Therefore, when the signal is cut off and input again, the gain of the variable gain tank 1 changes from the maximum gain to the stable state gain as shown in FIG. During this time a, the output of the variable gain amplifier 2 is input to the discriminator 4 as a signal with a large amplitude as shown in () in Fig. 2, which may cause a discrimination error due to superimposed noise, etc. There is. For this reason, it is necessary to send idle link pulses that may cause identification errors during the time a.

For this reason, conventional optical receiving systems have the disadvantage that transmission efficiency deteriorates when the input signal is a burst signal.

(c3 Purpose of the Invention In view of the above-mentioned drawbacks, the purpose of the present invention is to provide an AGC method that can improve transmission efficiency when the input signal is a burst signal.

(d) Structure of the Invention In order to achieve the above object, the present invention allows the AGC circuit to operate as before while a digital signal is being input, and also to digitize and store it, and when the signal is interrupted,
The above memorized content is converted into an analog signal, and the gain No. 1 is controlled to control the gain of the variable amplifier, so that the transient response is minimized, and when the next burst-like signal is received, it starts from the first bit. It is characterized by being able to receive data without errors.

(e) Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

Fig. 3 is a block diagram of the main parts of the optical receiving system according to the embodiment of the present invention, and Fig. 4 shows the switching state of the switch circuit and the signal flow while the signal is input and when the signal is cut off in Fig. 3. figure,
Figure 5 is a time chart of each part in Figure 3 when a burst signal is input, where (4) is the optical input signal, (B) is the output amplitude of the variable gain amplifier, and (0 is the output amplitude of the variable gain amplifier). Shows the gain.

Components with the same functions as those in Figure 1 are designated by the same symbols. 05 is a switch circuit, and 6 is a digital-to-analog converter (hereinafter referred to as D).
7 is an analog/digital converter (hereinafter referred to as an A/D converter), 8 is a memory, and 9 is a signal disconnection detection circuit.

While the digital signal is input, the signal disconnection detection circuit 9
Under the control of , the switch circuit 5 is connected as shown in FIG. 4 (5) so that the AGC circuit 3 operates as before, and the output of the AGC circuit 3 is converted into a digital signal by the converter 7 and stored in the memory. 81. Write the information. The information written in this memory 8 is updated one after another. When the signal is disconnected, the signal disconnection detection circuit 9 detects this, controls the switch circuit 5, and switches the connection as shown in FIG. 4). As a result, writing of the output of the AGC circuit 3 to the memory 8 is stopped, and the AGC circuit 3 written last to the memory 8 is stopped.
The gain of the variable gain amplifier 2 is controlled by the value obtained by converting the digital value of the output into analog by the D/A converter 6. Therefore, even if the burst signal shown in FIG. The gain of the amplifier 2 hardly changes as shown in Fig. 5 (O), and therefore the amplitude of the output of the variable gain amplifier 2 also changes
As shown in B), the discriminator 3 can identify without error from the first bit of the input digital signal without any change. Therefore, there is no need for idle link pulses, etc., and the transmission efficiency is improved.The signal disconnection detection circuit 9 may be provided at a location where a signal disconnection can be detected, such as at the output of a timing extraction circuit if there is one.

(f) Effects of the Invention As explained in detail above, according to the present invention, when a burst signal is transmitted, it can be identified from the bit of the first input signal in the optical receiving system, so the transmission efficiency can be improved. There is.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the main parts of a conventional optical receiving system, Fig. 2 is a time chart of each part of Fig. 1 when a burst signal is input, and Fig. 3 is a block diagram of the optical receiving system of an embodiment of the present invention. Figure 4 is a block diagram of the main part, and Figure 4 is a diagram showing the switching state of the switch circuit and the signal flow while the s signal is being input and when it is off. This is a time chart of each part of the circuit in Fig. 3 at the time of input.In the figure, 1 is a light receiving element, 2 is a variable gain amplifier, and 3 is an AGC.
circuit, 4 is a discriminator, 5 is a switch circuit, 6 is a digital-to-analog converter, 7 is an analog-to-digital converter,
8 indicates a memo 1c. 9 indicates a signal disconnection detection circuit. 1st drunkenness 2nd figure 4 ” ” 5 shi■ (Su

Claims (1)

[Claims] In an optical receiving system for digital signals having a variable gain amplifier and an AGC circuit that makes the amplitude of the output signal of the variable gain amplifier constant, a signal loss detection circuit that detects a signal loss, an analog-to-digital converter, and a digital - An analog converter, a memory, and a switch circuit are provided, and when a signal is being received, the gain of the variable gain amplifier is controlled by the AGC circuit, and the output of the AGC circuit is converted into a digital signal by the analog-to-digital converter. Converts it into a signal and writes it to the memory, and when the signal is cut off, the switch circuit switches,
The output of the AGC circuit is not input to the variable gain amplifier and the analog/digital converter, and the signal obtained by converting the contents of the memory into an analog signal by the digital/analog converter is input to the variable gain amplifier. An AGC method characterized by adding controllable gain to the filter.