JPS606138B2 - Common control automatic gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a common control automatic gain control circuit, and more particularly to a circuit that performs common automatic gain control by varying a power supply current that is multiplexed from a distance.

Generally, this type of automatic gain control circuit is used in carrier communication equipment to compensate for amplitude distortion caused by temperature fluctuations in the line. Since it can be easily constructed, it is advantageous for reducing the size and cost of the repeater, and is particularly effective for baseband transmission such as image transmission.

Conventionally, in this common control automatic gain control method, a pilot signal is sent through the transmission line, a deviation of the pilot signal level from the reference level is detected at the end station, and the signal is applied to the intervening line (a line installed separately from the transmission line). By changing the flowing current and controlling the variable equalizer by changing the resistance value of the thermistor, the gain of the repeater was changed and the distortion during vibration was equalized.

However, with such a conventional common control automatic gain control system, it is difficult to downsize the thermistor and reduce power consumption, and the reliability is also not very good.

In order to solve the above-mentioned conventional problems, an object of the present invention is to provide a common control automatic control system that performs automatic gain control by changing the current value supplied to the distant duplex power supply, thereby achieving miniaturization, lower power consumption, and improved reliability. An object of the present invention is to provide a gain control circuit.

Next, the present invention will be explained in detail with reference to the drawings.

First, a multiplex power supply system to which the present invention is applied will be explained. In this method, the transmission line is supplied with a signal, a feed current, and a pilot, and no intervening pair such as a slave is used. Therefore, in this method, when a deviation in the pilot signal level from the specified value due to temperature etc. is detected at the terminal station, the power supply current supplied to the transmission path is changed, and this power supply current change is detected by the repeater. Therefore, a circuit that changes the gain is required. FIG. 1 is a circuit diagram showing an embodiment of the present invention that detects such current changes and automatically changes the gain.

In FIG. 1, the output terminal of a main amplifier circuit 1 including a repeater variable equalizer having an input terminal la for the main signal is connected to a power supply separation circuit 2, a constant voltage detection circuit 3, and resistors R, to R6. Automatic gain control detection circuits 4 (hereinafter referred to as AGC detection circuits) are connected in parallel.

Further, a constant voltage circuit 5 is connected to the main booster circuit 1.
This constant voltage circuit 5 includes a power supply separation circuit 2 and a constant voltage circuit 6.
The constant voltage circuit 6 is connected to the constant voltage detection circuit 3. Reference numeral 7 denotes an automatic gain control comparison and increase circuit (hereinafter referred to as AGC comparison and increase circuit). ~R6, and is also connected to the main increase circuit 1.

Further, 8 and 9 indicate contact points, and 10 and 11 indicate output terminals. In addition, in this embodiment, a power supply current is supplied from terminals 10 and 11, and (-) which is not shown in FIG.
After being collected in a line, the signals are supplied to terminals 10 and 11 of the next stage repeater via terminal la. Therefore, this feeding current has no effect on the variable equalizer in the main amplifier circuit 1.
An example of such a power supply system is
Nippon Telegraph and Telephone Public Corporation technical research materials released in 1984
02, 09 “Videophone baseband transmission system”, Part 3
4, 5, and 1 on page 79 of the Section (Power Supply System), and in this figure, the aforementioned power supply separation circuit 2 is composed of two transistors TBI and TR2 ( Note that since the direction of the feeding current is opposite between FIG. 1 of the present application and the above-mentioned document, the two transistors TR1,
The emitter and collector of TR2 have been swapped). According to the common control automatic control circuit according to the first embodiment having the above-mentioned configuration, the electrical current supplied remotely is separated by the power supply separation circuit 2 and applied to the constant voltage circuit 5. The constant voltage circuit 5 converts the current into a constant voltage and supplies it to the main booster circuit 1. On the other hand, the constant voltage circuit (control circuit) 6 compares the voltage supplied from the constant voltage circuit 5 with the detected voltage of the constant voltage detector 3, and based on the comparison result, the voltage supplied from the power supply separation circuit 2 to the constant voltage circuit 5 is determined. Controls the current that flows. More specifically, if the output of the detector 3 becomes larger than the output of the constant voltage circuit 5, the current flowing from the separation circuit 2 to the circuit 5 is controlled to be small, and in the opposite case, the current is controlled to be large. As a result, the voltage between the connection points 8 and 9 is controlled to be constant by the auto-bias function of the transistor constituting the power supply separation circuit 2. This constant voltage between the connection points 8 and 9 is applied to the terminal 10 as described later.
, 11, the AGC detection circuit 4 detects the change in the power supply current supplied from the
It is used as a reference potential when detecting. The constant voltage circuit 6 includes a comparison amplification circuit that compares the outputs of the detector 3 and the constant voltage circuit 5, and a transistor that separates a part of the current supplied from the power supply separation circuit 2 to the constant voltage circuit 5 based on the comparison output. It consists of

As such a constant voltage circuit 6, for example, the
The circuits shown in Figures 34 and 67 on page 886 of the Solid State Handbook published by Maruzen Co., Ltd. on May 10th are applicable.
Correlating the circuit described in this document with the circuit in Figure 1, we get
The reference voltage side (10) described in the literature is the constant voltage circuit 5 in Fig. 1 of the present application.
The (1) side corresponds to the line connected to the constant voltage detection circuit 3. The line from the power supply separation circuit 2 to the constant voltage circuit 5 is connected from the unstable side (10) to the transistor Q. Corresponding to the line that reaches the reference side voltage (10) via the resistor R, the line that branches from the separation circuit 2 to the constant voltage circuit 5 and connects to the constant voltage circuit 6 is compared via the resistor R. Corresponds to a line leading to one terminal of a circuit. With this configuration, the current supplied from the power supply separation circuit 2 to the constant voltage circuit 5 is controlled by the output of the comparator in the constant voltage circuit 6. In addition, the first
In the figure, in order to make it easier to understand the current control from the power supply separation circuit 2, the current from the power supply separation circuit 2 is shown partially separated into the constant voltage circuit 6, but the specific circuit is , can be configured with a comparator and a transistor as described above. Therefore, in such a common control automatic gain control circuit, the voltage between the connection points 8 and 9 is constant as described above, but the output terminals 10, 1 1 of the resistors R 3 and R 4 forming the AGC detection circuit 4 Since the voltage between them changes depending on the change in the supply current, the voltage between the midpoint of resistors R5 and R6 and the connection point 8
The AGC comparison/amplification circuit 7 compares and intensifies the potential at the midpoint of the resistors R, .

This comparative amplification signal is sent to the variable impedance element (field-effect transistor (FET) or diode) of the variable equalizer, which changes the gain of the repeater by changing the amount of sieving of the variable equalizer. Equalization is carried out.In this case, the current change of the common control automatic gain control changes a part of the power supply current, so the potential between the connection points 8 and 9 is kept constant, and the AGC comparison increaser circuit Since the gain of 7 can be freely selected, by using relatively small resistances for the resistors R3 and R4 of the AGC detection circuit 4, the impedance change of the repeater at the output terminals 10 and 11 is kept small by 4, and the longitudinal current This is advantageous because it eliminates changes in the amount of attenuation.Also, generally, the input and output of the repeater is connected to the AGC with a snow protection resistor added.
If lightning protection resistors are used in the detection circuits R3 and R4, the configuration will be simplified. FIG. 2 is a block diagram of the second embodiment. In FIG. 2, the same parts as in FIG.

In Figure 2, 12 is the resistance R? ~R,. The AGC detection circuit 12 includes resistors R7 to R, . are connected to the power supply separation circuit 2 and also constitute the AGC detection circuit 12, including resistors R7 and R8.
The midpoint and the midpoint between resistors R9 and R,o are connected to the AGC comparison/amplification circuit 7, and 13 indicates an output terminal. In the common control automatic gain control circuit according to the second embodiment, the AGC detection circuit in the first embodiment is a balanced circuit, but as shown in FIG. 2, it is an unbalanced circuit.

Therefore, in the second embodiment of FIG. 2, the circuits corresponding to the constant voltage detection circuit 3 and constant voltage circuit 6 in FIG. 1, which are necessary when the AGC detection circuit is a balanced circuit, are not connected. In other words, the resistance R9 before the supply current changes
Assuming that the voltage at the connection point between and RIO is V13, and the voltage at the connection point between resistors R7 and R8 is V12, the voltage at each connection point after the supply current changes is V13' and V12' + RI1・△
1, the potential at the connection point between resistors R7 and R8 increases, and the equalization amount of the variable equalizer can be adjusted by this difference voltage. Therefore, in the unbalanced configuration shown in FIG.
A configuration for constant voltage as shown in the configuration shown in FIG. 1 becomes unnecessary.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and has various applications and modifications, and in the first embodiment, the connection points 8 and 9 are fixed with a constant voltage circuit for ease of explanation. However, it is not limited to making the connection points 8 and 9 a constant voltage, and instead of using a variable equalizer, the impedance of the feedback circuit of the main amplifier circuit can be changed by the output signal of the AGC comparison amplifier circuit. The gain may be changed by changing the gain. As explained above, the present invention is configured to detect a change in the value of a current supplied remotely, change the impedance of a field effect transistor, diode, etc., swing a variable equalizer, and perform automatic gain control. Miniaturization has the effect of reducing power consumption and improving reliability, as well as being relatively simple to configure.Brief explanation of the drawings The drawings show a common control automatic gain control circuit according to the present invention. 1 is a block diagram of the first embodiment, and FIG. 2 is a block diagram of the second embodiment.

1... Main amplifier circuit including variable equalizer of relay stand,
2...Power separation circuit, 4, 12...A
GC detection circuit, 5... Constant voltage circuit, 7...
・・AGC comparison increase circuit.

Figure 1 Figure 2

Claims (1)

[Claims] 1 A relay that detects a deviation in the pilot signal level from a specified value at a terminal station, changes the duplex feed current supplied on the transmission path, detects this current change at a repeater, and performs common control automatic gain control. In the amplifier circuit, an automatic gain control detection circuit connected to the main amplification circuit and the feed separation circuit and detecting changes in the feed current compares and amplifies the potential at the midpoint of the resistor constituting this automatic gain control detection circuit. A common control automatic gain control circuit comprising: an automatic gain control comparison amplification circuit that supplies a gain control signal to a variable equalizer forming a part of the main amplification circuit.