JPS645774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control amplifier used in digital transmission interrupters, etc. In particular, the present invention relates to an automatic gain control amplifier used in a digital transmission interrupter, etc. In particular, a pulse train of a digital signal with a DC component cut is input, and the gain is changed by a control signal to maintain a constant amplitude. This invention relates to a waveform amplitude detection method for detecting the amplitude of the output waveform of an AGC amplifier in order to obtain a correct control signal for an automatic gain control (AGC) amplifier that outputs an output signal.

In digital transmission systems that transmit information using pulses, so-called regenerative relaying is performed in which pulses that have suffered transmission loss and waveform distortion through a transmission line are regenerated into regular pulses. Regenerative relay uses an equalizing amplifier that equalizes loss and waveform distortion, and the output of the amplifier is required to have a constant amplitude and waveform.

In general, transmission loss and waveform distortion in a transmission line change depending on the characteristics of the transmission medium and the transmission distance, so a pulse train of a digital signal is input to an equalizing amplifier, and the gain is changed using a control signal to output a signal with a constant amplitude. An automatic gain control amplifier (hereinafter referred to as AGC amplifier) that outputs .

Figure 1 shows a conceptual diagram of an equalization amplification system with AGC function. In the figure, the amplitude value of the output signal of AGC amplifier 1 is detected by waveform amplitude detector 2, and the detected output is amplified by DC amplifier 3 as necessary and used as a control signal.
Control the gain of AGC amplifier 1 and as a result
It operates so that the waveform amplitude of the AGC amplifier output is kept constant. The present invention relates to a waveform amplitude detection method for correctly detecting the amplitude of the output waveform of the AGC amplifier 1 in order to obtain a correct control signal for the AGC amplifier 1 used in such applications.

Now, the codes used for digital transmission are:
Bibolar signals that do not have a DC component are often used, but with the diversification of information transmission in recent years, code structures that have a DC component and have high transmission efficiency have begun to be used. For example, an NRZ code that has a DC component but is not constant. in this case,
If marks or spaces continue for a long time in the transmitted PCM signal, the average mark rate of the signal on the transmission line will not be constant, and the DC component of the PCM signal on the transmission line will fluctuate. It becomes difficult to generate. Furthermore, since the frequency components of the PCM signal span a wide band from direct current to high frequencies, the AGC amplifier is required to have wide band characteristics, making the configuration complex. For this reason, AC-coupled AGC amplifiers that cut out DC components and transmit only AC components are commonly used in digital signal transmission paths. Input and amplify the pulse train with this DC component cut out.
The waveform of the pulse train of the AGC amplifier output signal is
There is no rapid fluctuation in the envelope, but so-called wandering (fluctuation) occurs in which the envelope fluctuates slowly. In order to prevent the influence of this output wandering, as shown in Figure 2, a method is used in which a DC regeneration circuit is provided to regenerate the DC component of the output signal, and then the peak is detected to obtain the control signal for the AGC amplifier. . The output waveform of the AGC amplifier 4 is subjected to peak detection by the peak detector 7 after DC wandering is eliminated by the DC regeneration circuit 6 of the waveform amplitude detector 5.
Furthermore, the DC is amplified by the DC amplifier 8, and its output is
The gain of the AGC amplifier 4 is controlled to keep the output waveform amplitude of the AGC amplifier 4 constant.

This method requires a DC regeneration circuit in the AGC amplifier, making the circuit configuration complicated.

The present invention eliminates the above-mentioned drawbacks and provides a method for obtaining a correct control signal for an AGC amplifier for an input pulse train in which the DC component is cut but wandering is superimposed. The purpose of the present invention is to provide a waveform amplitude detection circuit capable of correctly detecting the amplitude of the output of an amplifier. means 16 for detecting the value g, means 17 for detecting the negative peak value h of the other branched signal f, and the two detected peak values g,
The apparatus is characterized in that it includes means 18 for taking and outputting a difference i between h and outputting the difference i, and uses the difference i as a control signal for controlling the gain of the AGC amplifier 13.

The present invention will be explained below based on the drawings.

FIG. 3 shows an embodiment of the present invention, in which 9 is a transmitting side amplifier that outputs a digital signal with DC components cut off, 10 is an output terminal, 11 is a transmission line, and 12
is an input terminal of the AGC amplifier board 21, 13 is an AGC amplifier, 14 is an output terminal, 15 is a branch circuit that branches the output signal into two, 16 is a peak detector for the positive side waveform (hereinafter referred to as a + side peak detector), 17 is a negative side waveform peak detector (hereinafter referred to as negative side peak detector), 18 is a differential circuit, and 19 is a DC amplifier (hereinafter referred to as a negative side peak detector).
20 is a control voltage input terminal of the AGC amplifier 13, and 21 is an AGC amplifier board.

Figure 4 is an explanatory diagram of Figure 3, where a to i correspond to a to i in Figure 3, a and b are the input and output PCM signals of the AGC amplifier board 21, and a is the input side PCM signal. Output waveform of the digital signal with the DC component cut, which is output from the amplifier 9 on the transmitting side to the transmission line 11, b
is the output of the AGC amplifier 13, and at the same time is the output waveform of the digital signal with the DC component cut, which is also output from the output terminal 14 of the AGC amplifier board 21.
c is received at the input terminal 12 of the AGC amplifier board 21.
Input waveform input to AGC amplifier 13, d is AGC
Output waveforms of the amplifier 13, e and f are waveforms obtained by branching waveform d in a branch circuit, g is a waveform obtained by peak detection of the positive side of waveform e, h is a waveform obtained by peak detection of the negative side of waveform f, and i is the difference. Shows the output waveform of the circuit. Note that d, e, and f indicate only the envelope of the pulse train.

In Figures 3 and 4, the DC-cut PCM signal a output from the amplifier 9 on the transmitting side passes through the output terminal 10 - the transmission line 11 - the input terminal 12, and then passes through the AGC amplifier that cuts off the DC component with a waveform as shown in c. 13, and its output waveform d becomes a waveform in which DC wandering is superimposed with a gently varying envelope. This waveform d is branched into waveforms e and f by a branch circuit 15, and e is detected by a + side peak detector 16 to output a detected waveform g. On the other hand, f is detected by the negative peak detector 17 and outputs a detected waveform h. These waveforms g and h are each input to a difference circuit 18, and differential processing is performed to take the difference between them, the influence of DC wandering is canceled out, and the amplitude value of the waveform itself is outputted as waveform i. This waveform i is input to the AGC control input terminal 20 via the DC amplifier 19 and is subjected to transmission loss and waveform distortion in the transmission line 23.
The loss and waveform distortion of the PCM received signal waveform c are equalized and amplified, and the PCM signal b with a constant amplitude is output from the output terminal 14.
is output.

Note that the fifth detector is used as a peak detector and a differential circuit.
Generally well-known circuits as shown in FIGS. 7 to 7 may be used. FIG. 5 is an example of a positive side peak detector, and FIG. 6 is an example of a negative side peak detector. Further, as the subtraction circuit, an addition circuit or an operational amplifier as shown in FIG. 7 may be used.

As explained above, according to the present invention, it is possible to accurately detect the waveform amplitude of the output of an AGC amplifier that AGC amplifies an input pulse example in which DC wandering is superimposed with the DC component cut, and to obtain a correct control signal. Since the conventional complicated DC regeneration circuit can be omitted, the control circuit that generates the control signal can be included.
The configuration of the AGC amplifier board can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of a conventional AGC amplifier, Fig. 2 is a conceptual diagram of an AGC amplifier using a conventional DC regeneration circuit, Fig. 3 is an embodiment of the present invention, and Fig. 4 is a conceptual diagram of an AGC amplifier using a conventional DC regeneration circuit.
An explanatory diagram of the figure, Fig. 5 is an example of a + side peak detector,
FIG. 6 shows an example of a negative peak detector, and FIG. 7 shows an example of a differential circuit. In the figure, 1 and 4 are AGC amplifiers, 2 and 5 are waveform amplitude detectors, 3 and 8 are DC amplifiers, 6 is a DC regeneration circuit, 7 is a peak detector, 9 is an amplifier, 10 and 14
is an output terminal, 11 is a transmission line, 12 is an input terminal, 1
3 is a variable gain amplifier, 15 is a branch circuit, 16, 1
7 is a peak detector, 18 is a subtraction circuit, 19 is DC
Amplifier, 20 is AGC control input terminal, 21 is AGC
Amplification board, D1 is diode, C1 is capacitor,
Tr ₁ and Tr ₂ indicate transistors. In addition, the symbols a and b in the figure are PCM signals, a is the output waveform of the amplifier 9 on the transmitting side, b is the output waveform output from the output terminal 14 of the AGC amplifier board 21, and c is the waveform received at the input terminal. Received input waveform, d is the output waveform of the AGC amplifier 13, e and f are waveforms where waveform d is branched by a branch circuit, g is the waveform that detected the positive side peak of waveform e, and h is the negative side peak detected of waveform f. waveform,
i indicates the output waveform of the differential circuit 18.

Claims (1)

[Scope of Claims] 1. An automatic gain control amplifier that inputs a pulse train c of a digital signal with a DC component cut out, changes the gain according to a control signal 20, and outputs an output signal b with a constant amplitude, comprising: means 15 for branching the signal b into two; means 16 for detecting the peak value g on the positive side of one of the branched signals e; and means 17 for detecting the peak value h on the negative side for the other signal f;
A waveform amplitude detection method, comprising means 18 for taking and outputting a difference i between the two detected peak values g and h, the difference i being used as a control signal 20 for the automatic gain control amplifier.