JPS63196103A - Gain adjustment circuit for amplifier - Google Patents

Abstract

PURPOSE:To facilitate the gain adjustment and to attain remote control by using a pushbutton switch, an up-down counter operated in response to the operating mode and a semiconductor variable resistive element in response to the count. CONSTITUTION:In applying intermittent control to the pushbutton switch 12, a monostable multivibrator 13 is activated continuously, a logic '1' is given to an AND gate 10, the up-down counter 15 receives a pulse of a pulse generator 9 and its count is incremented. In releasing the switch 12, the counter stops at the count. When the count reaches 15, the count is stopped. A decoder 19 updates its decoding in response to the count and its signal is converted into a digital level signal by a resistance circuit network 20 and given to a semiconductor variable resistive element (FET) 8 through a voltage controlled circuit 21. The resistance of the FET 8 is increased gradually as the count is incremented and the gain of amplifiers 2A, 5A and the gain at that time is maintained by releasing the switch 12. In operating the switch 12 consecutively, an integration circuit 14 gives a level '1' to the AND gate 11, the count of the counter 15 is incremented and the gain is deceased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circuit for adjusting the gain of an amplifier.

(Prior Art) As a gain adjustment circuit for a conventional amplifier such as a telephone, there is a circuit as shown in FIG.

In the figure, 1 is a signal input terminal, 2 is an amplifier, 3 is a resistor, 4 is a variable resistor for gain adjustment, 5 is an amplifier, and 6
is the signal output terminal.

A signal input to the input terminal 1 is amplified by the amplifier 2, divided by the resistance value of the resistor 3 and the resistance value of the variable resistor 4, and then amplified by the amplifier 5 and output from the output terminal 6. . The gain of the signal at the output terminal 6 is then adjusted by the variable resistor 4.

As the variable resistor 4, a rotating type variable resistor or a sliding type variable resistor is used, and by moving the sliding piece 7 and changing its resistance value, the voltage division ratio with the resistance value of the resistor 3 can be adjusted. to adjust the gain of the signal at the output terminal 6.

(Problems to be Solved by the Invention) However, in the circuit with the above configuration, the operation of the variable resistor is cumbersome because it requires rotation or sliding. Since it is necessary to install the variable resistors in combination, there are problems in that the installation locations of the variable resistors are limited and remote control is not possible.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned problems, it is an object of the present invention to provide a circuit in which the gain of an amplifier can be adjusted by operating a push button switch.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a semiconductor variable resistance element which serves as a resistance element for gain adjustment of an amplifier and whose resistance value is set in accordance with a control signal thereof. , a pushbutton switch whose operation specifies adjustment of the gain of the amplifier; and a pushbutton switch that determines whether the pushbutton switch is operated intermittently or continuously with a cycle shorter than a predetermined cycle and sends corresponding operation signals over each operation period. an operation signal output circuit that outputs, a pulse generator that continuously generates pulses of a constant period, and an increasing direction starting from the counted value held over the output period of each operation signal according to each operation signal. an up/down counter that counts the pulses or counts them in a decreasing direction until the next operation signal is output; and a control that outputs the control signal in a predetermined correspondence with the count value of the up/down counter. It consists of a signal circuit.

(Function) According to the present invention, when the pushbutton switch is operated continuously or continuously, the up/down counter increases the pulse of the pulse generator based on the count value before the operation according to each operation mode. When the operation period is completed by counting in the direction or in the direction of decreasing, the counted value is held until the next operation. The resistance values of the semiconductor variable resistance elements are controlled by receiving control signals from the control circuit according to the count values of the up and down counters, and the gain of the amplifier is adjusted to a value based on these resistance values. .

(Embodiment) FIG. 1 is a gain adjustment circuit diagram showing an embodiment of the present invention.

In this figure, parts that have the same names and are equivalent to those in FIG. 2 are indicated by the same reference numerals with a suffix A added thereto, and hereinafter, the different parts will be mainly explained.

8 is a FET as a semiconductor variable resistance element, and an amplifier 5A
The amplifier 2A is connected between the input terminal of the amplifier 2A and the ground, basically forming a resistance element equivalent to the variable resistor 4 of FIG.

5A, and the drain D in the operating voltage range is adjusted according to the value of the gate terminal G.
The resistance value between the source S and the source S is determined.

Reference numeral 9 denotes a pulse generator that continuously generates pulses with a period of approximately 1 second, and serves as an input to each of the AND gates 10 and 11. Reference numeral 12 denotes a push button switch, which is used to adjust and designate the gain A related to the amplifier 2.5 by pressing the switch, and outputs a logical value of "1" when pressed, and outputs a logical value of "O" when released. . 1
3 is a retriggerable monomulti, which serves as the other input of the AND gate 10, and outputs approximately 0,
If it receives "1" and "O" intermittently with a cycle of 5 seconds or less, it will output "1" continuously, and if it receives "1" continuously, it will output "1" once, but then becomes “O”. 14
is an integral circuit which serves as the other input of the AND gate 11, and outputs "1" when "1" is continuously received from the pushbutton switch 12; , remains "0". 15 is an up/down counter consisting of a 4-bit binary counter, and its up terminal U receives the output of the AND gate 10 via the OR gate 16, and during the period when the monomulti 13 is "1", The pulses from the pulse generator 9 are received and counted in the increasing direction. The down terminal receives the output of the AND gate 11 via the OR gate 17, and receives the pulses from the pulse generator 9 during the period when the integrating circuit 14 is "1" and counts in the decreasing direction. . 18 is a gate circuit, up/down counter 1
5, and when the count value is 1 to 14, each terminal U, D is "0", and when the count value is 15, "1" is given from the terminal U to the OR gate 16, and the mono multi 1
Up/down counter 15 when the output of 3 is “1”
When the count value is 0, "1" is given to the OR gate 17 from the terminal, and the counting of the up-down counter 15 is stopped when the output of the integrating circuit 14 is "1". A decoder 19 decodes the 4-bit code of the up/down counter 15 into 16 ways. 2
0 is a ladder-type resistor network that converts the signal from the decoder 19 into control signals of each digital level. ■ is the power supply for the conversion. The decoder 19 and the resistor network 20
forms a control signal circuit. Reference numeral 21 denotes a voltage control circuit which adjusts the offset voltage and working voltage range for the control signal of the resistor network 20 and applies it to the gate G of the FET 8. FE
At T8, as the count value of the up/down counter 15 increases, the resistance value between the drain D and the source S increases due to the signal from the gate G, thereby increasing the gain A in related to the amplifier 2.5.

Next, the operation of the circuit shown in FIG. 1 will be explained.

The pulse generator 9 continuously generates pulses. The pushbutton switches 12 each have a logic value of "0" when not operated, and therefore the monomulti 13. Integrating circuit 14
are both "θ", and the up/down counter 15 holds the count value of the previous state and stops.

When the pushbutton switch 12 is operated intermittently to increase the gain associated with the amplifier 2.5, the monomulti 13 operates continuously, giving a logical value of "1" to the AND gate 10, and increasing the up/down counter 15. is and gate 10. Through the OR gate 16, the pulse generator 9
A pulse is received at the up terminal U, and the count value increases each time it rises.

Then, when the push button switch 12 is released, the count value stops at that time. Further, by continuing to operate the push button switch 12 intermittently, when the count value of the up/down counter 15 reaches 15, "1 degree" is applied from the terminal U of the gate circuit 18 to the OR gate 16, and the operation similarly stops.

The decoder 19 updates the decode according to the code signal output as the count value of the up/down counter 15, and the signal of the decoder 19 is converted into a digital level signal by the resistor network 20, and the signal is converted to a digital level signal via the voltage control circuit 21. It is applied to the gate terminal G of FET8.

In the FET 8, the resistance value between the drain D and the source S increases sequentially as the count value of the up/down counter 15 increases, and the A gain related to the amplifier 2.5 increases. When the push button switch 12 is released and the up/down counter 15 stops counting, the gain at that time is maintained.

Next, in order to lower the gain, push button switch 12
When continuously operated, the integration circuit 14 gives "1" to the AND gate 11, and the up/down counter 15 outputs "1" to the AND gate 11. Through the OR gate 17, the pulse generator 9
When the down terminal receives a pulse, the count value decreases.

Then, when the push button switch 12 is released, the count value stops at that time. Also, when the push button switch 12 is kept pressed and the count value of the up/down counter 5 reaches O, "1" is transferred from the terminal of the gate circuit 18 to the OR gate 17.
and stop as well.

In the same way as above, a signal based on the count value of the up/down counter 5 is applied to the gate G of FET8,
In the ET8, the resistance value between the drain D and the source S sequentially decreases as the count value of the up/down counter 15 decreases, and the gain associated with the amplifiers 2 and 58A decreases. Then, when the pushbutton switch 12 is released, the gain at that time is maintained.

(Effects of the Invention) As explained above, according to the present invention, when the pushbutton switch is operated intermittently, the gain of the amplifier increases sequentially over the operation period, and when operated continuously, it decreases sequentially. The pushbutton switch has excellent operability, and the resistance element for gain adjustment is controlled by a control signal, and there is no need to provide a circuit related to the control signal near the resistance element. It can be installed anywhere and can be controlled remotely.

[Brief explanation of the drawing]

Figure 1 is a gain adjustment circuit diagram showing an embodiment of the present invention, Figure 2 is a gain adjustment circuit diagram showing an embodiment of the present invention.
The figure is a conventional gain adjustment circuit diagram. 2A, 5A...Amplifier 3A...Resistor 8...FET (semiconductor variable resistance element) 9...Pulse generator 12...Push button switch

Claims (1)

[Scope of Claims] A semiconductor variable resistance element that serves as a resistance element for adjusting the gain of an amplifier and whose resistance value is set in response to a control signal thereof; A pushbutton switch that specifies adjustment of the gain of the amplifier by operation; An operation signal output circuit that determines whether the pushbutton switch is operated intermittently or continuously at a cycle shorter than a predetermined cycle and outputs a corresponding operation signal over each operation period; a pulse generator that generates pulses; and a pulse generator that, depending on each of the operation signals, counts the pulses in an increasing direction or in a decreasing direction starting from the held count value over the output period of each of the operation signals, and performs the next operation. An amplifier gain adjustment circuit comprising: an up/down counter that holds a signal until it is output; and a control signal circuit that outputs the control signal in a predetermined correspondence with the counted value of the up/down counter.