JPS581310A - Driving circuit for automatic gain adjusting circuit - Google Patents

Abstract

PURPOSE:To eliminate variance of response characteristics by allowing an AGC circuit which uses a thermistor to have a sufficiently great time constant. CONSTITUTION:A pilot signal extracted through a pilot filter 1 is converted by a rectifier 3 into a direct current. This DC component is inputted to a DC amplifying circuit 7, whose output is amplified by an amplifier IC to control a transistor TR. Consequently, the current flowing through a thermistor 5 is controlled to hold the level of the pilot signal constant. To the feedback path of the amplifier IC, a capacitor C is connected, and the DC amplifying circuit 7 constitutes an analog integrating circuit having a large time constant. Therefore, variance of the response characteristics of the thermistor 5 are made much less than the time constant of the whole circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for supplying current to a thermistor in an automatic gain g* circuit, particularly in an automatic gain control circuit (hereinafter referred to as AGC) using a thermostat. Integration function added to DC amplifier.

The present invention relates to an automatic gain adjustment circuit drive circuit that allows the time constant of the entire AGC including the thermistor to be set with less variation.

Conventionally, an AGC') has been inserted into a transmission system to adjust the gain to a predetermined level.

For example, in an i-wave transmission system, there are many instantaneous interruptions of microphone ρ waves, so a pilot signal is added to the i-wave transmission system, and the pilot signal activates the AGC and eliminates the disturbance in the mi-goo wave transmission system. Detection is being carried out.

In the above AGC, for example, the pilot signal is amplified to control the current flowing through the circuit, and the gain of the gain adjustment section provided in the transmission path is adjusted. Since the response time constant of the -mister□ itself is relatively large, the time constant of the entire AGC is determined by the time constant of the -mister itself, which is the large one in the buffer.

The present invention aims to solve the above points.
, To add an integral function to the DC amplifier in the AGC, so that it can be designed using a relatively small capacity to provide the necessary time constant, and to provide the DC amplifier function, integral function, and tube. It is said that For this reason, (1) the automatic gain control circuit driving circuit of the present invention extracts a part of the signal current to a gain adjustment section provided in a transmission line through which the signal current flows. In the automatic gain 5kis circuit that performs feedback corresponding to the signal level of , there is a DC amplifier that amplifies an input signal corresponding to a part of the extracted signal current, and a gain adjustment section tm driven by the output of the DC amplifier. The current amplifier is characterized in that it is provided with a capacitive feedback circuit and operates as an integrating circuit that controls the current f11 flowing through the thermistor and integrates the input signal. The explanation will be given below with reference to the drawings.

FIG. 1 shows a configuration of an embodiment of the present invention, and FIGS. 72 and 3 are explanatory diagrams for explaining the operation of the configuration shown in FIG. 1.

In Figure 1, l is a pilot filter.

2 is an AC amplifier, 3 is a rectifier, 4 is a comparator that detects not just a momentary interruption of the pilot signal but a long-term disconnection due to a fault in the transmission path, 5 is a thermistor, and 6 is a component on the transmission path, TR is a transistor, R1 to R9 are each a resistor, C is a capacitor, and I
C represents an amplifier. Incidentally, the resistor tC and the resistor R4 correspond to a capacitive feedback circuit according to the present invention, the resistor R3 constitutes an input resistor, and the resistors R1 and R2 constitute a voltage divider that provides an input reference voltage to the DC amplifier circuit 7. constitutes,
The resistors R6 and R7 constitute a so-called semi-fixed bias circuit for the transistor jllTR, and the resistor R9 corresponds to a current limiting resistor that limits the maximum current 1i flowing through the thermistor TR.

The above-mentioned pilot signal is extracted by the pilot filter l, amplified by the AC amplifier 2, and the first stream 11
3, it is converted to direct current. Then, the DC component is
It becomes an input signal to the DC amplifier circuit 7, is directly amplified by the amplifier IC, and is controlled by the transistor T''Rfl.As a result, the current flowing through the thermistor 5 is controlled by the signal level of the pilot signal, and the gain adjustment section 6 The gain is controlled, that is, the signal level of the Virat signal is maintained at a predetermined level.

Also, not some of the above, but due to a failure in the transmission line.

When the output of the amplifier IC drops below a predetermined threshold,
Comparison lI4 detects this and issues an alarm l11.

As described above, the current amplifying circuit 7 controls the current flowing to the servo amplifier 5, but this is because the feedback circuit including the circuit is connected to the amplifier IC.

The DC amplifier circuit 7 constitutes the Anag integral calculation li]-, p
I'm here. The time constant is mainly determined by the capacitor C and the resistors R3 and R4.
Even if the capacitance of Funden "V"C is relatively small, the values of resistors R3 and R4 can be set large.
- It becomes possible to provide the AGC circuit with a sufficiently larger time constant than the response time constant of the mister 5 itself.

Further, the illustrated DC amplifying circuit 7 can control the current flowing through the thermistor 5 with the characteristics shown in FIG. That is, the maximum value of the current ITH flowing through the thermistor 5 is determined by the resistor R9, and the minimum value of the current ITH is substantially determined by the base current for the transistor TR caused by the resistor R6. Further, the slope shown in FIG. 2 is determined by resistors R3 and R4, and the center of the slope shown in the direction of the arrow shown in the figure is determined by the reference voltage level of resistors R1 and R2. For this purpose, the DC amplifier circuit 7 shown in FIG.

Resistance R1, R3! , R3, R-4, R6, and R9 can be set independently and used as an ik body to impart the characteristics of the new line.

Needless to say, since the circuit section including the amplifier IC tube constitutes an integral calculation circuit as shown above, a state in which the input level A temporarily drops due to a so-called instantaneous interruption occurs as shown in Fig. 3. too.

The level input to the comparison 194 is as shown in level B,
This results in a relatively large time constant tube. For this reason, by providing the threshold level for comparison 1B4 as shown in C in the figure, it becomes possible to issue an alarm only when a failure occurs, without issuing an alarm every time a momentary power outage occurs.

As explained above, according to the present invention, the steady state characteristics necessary for AGC can be freely set, and the time constant of the entire AGC can be set in a manner that is basically not affected by the response time constant of the thermistor itself. It becomes possible to set.

ms explanation of the ttm plane, FIG. 1 shows an example configuration of the present invention, and FIGS. 2 and 3 show explanatory diagrams explaining the operation of the configuration shown in FIG. 1.

In the diagram, 4 is comparative theory, 5 is Mr., and 6 is interest 1llllI
Part I1, 7 is a DC amplifier circuit, and TR is a transistor.

IC represents an amplifier, and C and R4 represent a capacitive feedback circuit.

Patent applicant: Fujitsu Limited Representative Patent Attorney Mori 1) Hiroshi

Claims (1)

[Claims] an automatic gain that extracts a part of the signal current and feeds it back in accordance with the signal level of the part of the signal current to a gain adjustment section provided in a transmission path through which the signal current flows;
A DC amplifier 1Ill+ for amplifying an input signal corresponding to a part of the extracted signal current by controlling the adjustment circuit, and a 1V-1 star driven by the output of the experimental DC amplifier to control the gain adjustment section. In addition to providing the above-mentioned DC increase II
1. An automatic gain adjustment circuit driving circuit, characterized in that the device is provided with a combinant feedback circuit, and operates as an integrating circuit that controls the current flowing through the thermistor and integrates the input signal.