JPS5844644Y2 - PCM regeneration repeater - Google Patents

Description

[Detailed description of the invention] The present invention relates to a circuit that realizes good characteristics of transmission equipment having an AGC function, and its purpose is to:
It has a simple circuit configuration and extremely stable identification characteristics.

An object of the present invention is to provide a PCM regenerative repeater that controls output restriction when there is no input signal.

In the first place, the purpose of the AGC circuit is to obtain a constant output amplitude or a constant output waveform with respect to input level fluctuations within a certain specified range.

Therefore, the gain of the AGC amplifier generally increases as the input signal level decreases, and the gain of the AGC amplifier is at its maximum when there is no input signal.

In other words, if noise arrives at the input under the condition that the normal input signal is no signal, there will be no problem if this noise does not exceed the predetermined discrimination level, but if it exceeds the discrimination level, If it were,
The noise behaves as if it were a regular input signal and becomes an output.

In other words, if there is a signal that exceeds the identification level, even if it is noise, a problem may occur in which a false output is generated.

Therefore, PCM that identifies and reproduces the input signal and outputs it.
In a regenerative repeater, the pseudo output due to the above-mentioned noise may be the same as a normal signal in terms of level, and its influence may become a hindrance in maintenance and monitoring of the transmission line.

As a countermeasure, it is necessary to design the AGC amplifier so as to suppress the surplus gain as much as possible.

Alternatively, countermeasures such as limiting the response range of the variable impedance element by adding a fixed resistor in series or parallel to the variable impedance element may be considered, but these measures minimize the so-called AGC output deviation within the required human power level range. This is inconsistent with trying to compress it.

In addition, no matter which method is used, the gain remains maximum when there is no input signal, and it is difficult to effectively solve the problem.

This problem can be solved by eliminating the output error signal when the normal input signal is no signal.

Therefore, a method can be considered in which the input signal is monitored, a no-signal state of the regular signal is detected, and the output is stopped in one of the devices based on the result.

The present invention solves this problem by connecting the DC amplifier output or the end voltage of the variable impedance element in the AGC closed loop to a comparator through a buffer, providing a clamp circuit after the AGC amplifier output, and using the comparator output to clamp the voltage. A circuit that controls the circuit and operates this clamp circuit when the AGC control voltage exceeds a specified level, that is, a circuit that directly applies the control voltage generated inside the AGC loop as a means of detecting the state of no input signal. By doing so, it is possible to provide a PCM regenerative repeater that has a simple circuit configuration, has a highly stable discrimination characteristic, and suppresses output when there is no input signal.

Generally, an AGC system has a feedback circuit configuration that detects the voltage peak or power of an output signal, converts it to a DC voltage, amplifies it, and drives a variable impedance element.

Therefore, the output of the DC amplifier that drives the variable impedance element, that is, the AGC control voltage, generates a DC voltage corresponding to the input signal level.

Diodes are widely used as variable impedance elements, and the driving direct current of the diode is controlled by the AGC control voltage, and a variable part is configured by changing the differential resistance or junction capacitance of the diode.

Due to the non-linear characteristics of the diode, A when there is no human input signal.
Since the GC control voltage or the diode end voltage appears as a sudden voltage change, these voltages can be used directly to control the clamp circuit.

This AGC control voltage or diode terminal voltage is given as a result of the peak value of the input signal voltage or power detection, and the detection system generally has a time constant circuit to prevent fluctuations due to instantaneous noise. , using this voltage for no-signal detection is essentially advantageous in terms of noise resistance, and has a significant effect compared to the method of suppressing the gain of the AGC amplifier as much as possible or the method of specifying the response width of the variable element. It gives rise to

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be explained in detail below with reference to an embodiment shown in the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a detailed circuit diagram that also partially shows blocks.

In the figure, 1 is an input terminal, A is an amplifier 2, and a signal detection section 3.
, a DC amplifier 4, and a variable impedance element 5, 6 is an AGC control voltage, 7 is a comparator, 8 is a signal processing circuit after the AGC output, and PCM
This is an identification and regeneration circuit in a regeneration repeater.

9 is an inhibit gate controlled by the output of comparator 7.

10 is an output terminal.

In the circuit configured as described above, when a normal signal level is applied to the input terminal 1, the AGC control voltage 6 shows a level within a certain regulation, and the output of the comparator 7 does not operate the inhibition gate 9, so the AGC control voltage Output is output to amplifier A.

On the other hand, when there is no input signal, the AGC control voltage 6 shows a special value, and the comparator 7 detects this and operates the inhibition gate 9. Even if there is, nothing will occur.

FIG. 2 shows a circuit diagram of a specific embodiment.

The feature of this embodiment is that an absolutely stable ground potential is used as the reference voltage of the comparator 7, and the difference between the AGC control voltage and this ground potential is level-shifted using diodes 11 and 12. diode 15.1
The point is that it compensates for temperature fluctuations caused by 6.

Furthermore, by connecting the AGC control voltage 6 to the comparator 7 via the emitter follower 13, a clamp control system is constructed without affecting the original AGC loop characteristics at all.

In addition, the output of the comparator 7 drives the transistor of the inhibition gate 9, and when the input signal is steady, this transistor is turned off.
When there is no signal, the final output 10 is clamped as conductive.

Incidentally, since the inhibition gate 9 only needs to control the final output 10, it is clear that the purpose can also be achieved by connecting it to various signal processing function stages after the signal processing circuit 8 after the AGC output. There is.

FIG. 3 is a control characteristic diagram based on an example of measured values in this embodiment, where the horizontal axis represents the relative level of the input signal to the input terminal 1, and the vertical axis represents the AGC control voltage 6.

This figure shows that the effective signal level region and the no-signal region can be easily distinguished by the AGC control voltage.

As explained above, according to the present invention, in an AGC system, the inconvenience that the gain of the AGC amplifier reaches its maximum when there is no input signal and pseudo output is generated due to noise input can be completely solved, and it can be This has a great effect on maintenance and monitoring of the AGC-equipped transmission equipment used.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a block diagram of the present invention, Fig. 2 is a partial block diagram and a partially detailed circuit diagram of an embodiment of the present invention, and Fig. 3 is a control characteristic diagram according to a one-sided regular example. It is. A: AGC control amplifier, 1: Input terminal, 2: Amplifier, 3: Signal level detection circuit, 4: DC Amplifier, 5...
- Variable impedance element, 6... AGC control voltage, 7... Comparator, 8... Discrimination regeneration circuit, 9... Inhibition gate, 10... ...Output terminal, 11.12, 15.16...Diode, 13.14...Emitter follower.

Claims (1)

[Claims for Utility Model Registration] An amplifier 2, a rectifying element connected to the output of the amplifier, which generates a DC control voltage proportional to the input signal, and a rectifying element that is sufficiently large for the repetition of the normal signal and that produces instantaneous peak noise. A signal detection circuit 3 including a time constant circuit having a sufficiently small time constant for peak repetition, a DC amplifier 4 connected to the signal detection circuit, and a non-circuit amplifier connected to the DC amplifier and driven by its output. An AGC amplifier A includes a series circuit of an impedance conversion element 14 having a linear characteristic and a variable impedance element 5, and a closed loop is formed by connecting the variable impedance element of the series circuit to the amplifier. The voltage at the end of the impedance element 5 is connected via the emitter follower 13 or the level shift diode 11.12 to a comparator 7 using the ground potential as a reference voltage and compared with the reference voltage of the comparator. A PCM regeneration device configured such that a clamp circuit 9 activated by the output of the comparator is connected to the output side of the discrimination regeneration circuit 8 connected to the output of the amplifier, and an output can be taken out depending on the presence or absence of a regular signal to the AGC amplifier. Repeater.