JPS62196910A - Automatic gain amplification control circuit - Google Patents

Abstract

PURPOSE:To avoid damages of a telephone receiver even in case the switch of a device is turned on while a setting volume for sound level is kept at the maximum value for a handset, etc., by reducing the gain of an amplifier circuit immediately after the device switch is applied and then increasing automatically said gain in some steps and for each fixed period of time. CONSTITUTION:The switch of a handset is turned on for a circuit test and at the same time a switch 14 is turned on. Then an analog switch control circuit 13 starts a counting action by the pulse supplied from a pulse generator 15 to control both analog switches 10-12 respectively every fixed period of time. These switches 10-12 are all turned off immediately after the switch 14 is applied. Then the switch 10 is first turned on and the output value is increased compared with the original state when a fixed time (counted time of the circuit 13) passed. Then the switch 11 is turned on after a fixed time with the switch 10 kept on. Thus the amplification degree of an amplifier circuit 3 is gradually increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an amplifier circuit that balances and outputs audio signals, etc., and in particular, adjusts the volume output level of a handset for a meeting on a microwave communication line by turning on the operation switch. rear,
The present invention relates to an automatic gain amplification control circuit that can automatically vary the gain.

[Conventional technology]

Conventionally, in a handset for a meeting on a microwave communication line, input signals V, , V are input to one input terminal of two output level setting amplifiers 1 and 2, as shown in FIG.
, and amplifies the difference between these input signals Vt+v2 and outputs each as an output voltage VOIJT. However, the amplification degree of this amplifier circuit 3 is always a constant value. Ta. Note that each of the amplifiers 1 and 2
A variable resistor 4 for gain setting and fixed resistors 8 and 9 are connected between the output terminals of
is inserted to adjust the volume level of each output.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional handset, the amplification degree of the amplifier circuit 3 is always constant, so when the handset is turned on during a line test, a high volume is output at the same time, and the handset such as a speaker is The disadvantage is that it can cause damage.

The present invention has been made to eliminate these drawbacks, and it is an object of the present invention to provide an automatic gain amplification control circuit that can automatically vary the audio output level of a handset after turning on the switch. be.

[Means for solving problems]

That is, the automatic gain amplification control circuit of the present invention is an amplifier configured to apply an input signal to one input terminal of two output level setting amplifiers, respectively, and amplify and output the difference between the two input signals. In the circuit, a plurality of gain setting resistors are connected in parallel between both ends of the gain setting resistor of the amplifier circuit, analog switches are provided for each of the gain setting resistors, and these analog switches are connected to the amplifier circuit. The present invention is characterized in that the gain of the amplifier circuit is automatically varied over time by sequentially operating the circuit at regular intervals at the same time as the circuit is operating.

[Effect]

Therefore, according to the present invention, by automatically varying the gain of an amplifier circuit over time, the gain is reduced immediately after the switch associated with the amplifier circuit is turned on, and the gain is reduced at regular intervals. The gain can be increased progressively over the stages.

〔Example〕

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

FIG. 1 is a circuit diagram showing an embodiment of an automatic gain amplification control circuit according to the present invention. In the circuit of this embodiment, an input signal v1. v2, and these two input signals vl, v2
The differential amplifier circuit 3 is configured to amplify the difference between the two and output them as the output voltage VOUT, which is similar to the conventional example shown in FIG. A plurality of gain setting fixed resistors 5, 6.7 are connected in parallel between both ends of the gain setting variable resistor 4, and an analog Insert switches 10, 11 and 12.

Further, an analog switch control circuit 13 consisting of a counter or the like is provided to control each of the analog switches 10, 11 and 12 to turn on and off at regular time intervals,
By sending pulses generated from a pulse generator 15, which is driven when an operation switch 14 interlocked with a switch (not shown) of a meeting handset is turned on, to the control circuit 13 as a time signal, the amplifier circuit The gain of 3 is automatically varied over time.

Therefore, in the circuit configuration of the above embodiment, when the switch of the handset is turned on during a line test, the switch 14 is turned on at the same time, and the pulses sent from the pulse generator 15 cause the analog switch control circuit 13 to
starts counting and controls each analog switch 10, 11 and 12 so that the timing as shown in FIG. 2 is obtained at regular intervals. At this time, when the amplifier circuit 3 starts operating, that is, immediately after the switch 14 is turned on, the analog switches 10, 11, and 12 are all in the off state, and the input signal vl is input.

The output voltage VOtlT due to v2 is determined by the resistance value of the variable resistor 4 being RAN, and the resistance value of the fixed resistors 8 and 9 being R and I, respectively.
Letting Rv, it becomes. Then, after a certain period of time (count time of the analog switch circuit 13) has elapsed, the analog switch 10 is first turned on (FIG. 2 (1)), and the output value becomes larger than the initial state. After a certain period of time has elapsed from this state, the analog switch 11 is turned on until the analog switch 10 is turned on (Fig. 2 (b)), and an output value that is further amplified than in the previous state is output. . In this way, the amplification degree t, b gain of the amplifier circuit 3 gradually increases, and the final value at which all the analog switches 10 to 12 are in the on state is determined by the gain setting fixed resistors 5 and 6.
If the resistance values of 7 degrees are respectively RB, Rc, and RD, then the temperature will stabilize. This prevents a high volume from being output at the same time as the handset is switched on, unlike in the prior art.

〔Effect of the invention〕

As explained above, the automatic gain amplification control circuit of the present invention has the following features:
Reduce the gain of the amplifier circuit immediately after turning on the device,
The gain can be automatically increased in several steps at regular intervals, so even if you turn on the switch with the volume level setting of the handset etc. set to maximum (MAX), the output sound l will change over time. At the same time, there is an effect that the large size does not damage the receiver such as the speaker.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a time sequence of an analog switch used in the operation of the above embodiment, and FIG. 3 is a circuit diagram showing a conventional example. . 1.2...Amplifier for output level setting, 3...Amplification circuit, 4...Variable resistor for gain setting, 5-9...
-Fixed resistor for gain setting, 10-12Φ...Analog switch, 13...Analog switch control circuit, 14...Switch, 15.Fist--Pulse generator.

Claims (1)

[Claims] In an amplifier circuit configured to apply an input signal to one input terminal of two output level setting amplifiers, and amplify and output the difference between the two input signals, the gain setting resistor of the amplifier circuit is A plurality of gain setting resistors are connected in parallel between both ends, and analog switches are provided for each of the gain setting resistors, and these analog switches are connected at a certain time interval at the same time as the amplifier circuit operates. An automatic gain amplification control circuit characterized in that the gain of the amplification circuit is automatically varied over time by sequential operation.