JPS58202615A - Gain control circuit - Google Patents

Abstract

PURPOSE:To realize an integrated semiconductor and at the same time to decrease the number of external connection terminals on the basis of such a design of circuit that decreases the number of component parts of an external circuit. CONSTITUTION:A voltage/current (V/I) converter 1 consists of 2 constant current circuits CS1 and CS2, 4 diodes D1-D4, and 4 transistors Q1-Q4. The voltage signal is applied to the V/I converter 1 as an input signal from an operational amplifier OP1, and this output signalis led out in the form of a current which flows to a variable resistor VR1. The resistor VR1 converts the output signal of the converter 1 into a voltage signal and supplies it to the 2nd operational amplifier OP2 which functions as a voltage amplifier. Therefore only are each of the external terminal No. 4 sufficies, and the number of external terminals is decreased compared with the conventional circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain allfi circuit suitable for use in various electronic detection equipment, such as audio amplifiers.

One of the gain adjustment circuits that have been controversial in the past has a circuit configuration as shown in the first factor.

In other words, a semiconductor integrated circuit (hereinafter referred to as an IO).

) are configured with two operational amplifier circuits OPI and op2. Then, the human power signal v1n is the first performance 11j
The output signal of the voltage amplified ζn1 by the width amplifier OPI flows to the ground line via the No. 1 terminal for external connection, the coupling capacitor C1, and the variable resistor VR,'i. Therefore, by adjusting the movable terminals of the variable resistor VR, the operational amplifier OP.

output signal or the desired voltage level coupling capacitor C2,
2nd terminal is fully closed and the 2nd operational amplifier circuit is opened.

will be supplied to. Therefore, from the output terminal of the second operational amplifier circuit op, there is an output signal system having a voltage level responsive to the adjustment of the variable resistor VR.

By the way, one of the technological trends in reducing the number of parts required for each multiple electronic circuit is to incorporate many functions into one part to increase the added value. In this way, it is multifunctional! In case of process C, the number of external connection terminals tends to increase due to human output signals, control signals, etc. The increase in external connection terminals
Semiconductor substrates become larger, and together with an increase in production man-hours and an increase in the number of parts to provide terminals, the production cost increases considerably3.Furthermore, the number of external connection terminals increases. For reducing labor costs to capacitors, coils, variable resistors, etc.〈1
This increases the possibility of using a large number of circuit components and makes wiring work more troublesome.

From the above-mentioned point of view regarding the IC, it is clear that the conventional variable gain adjustment circuit described above does not have a preferable circuit configuration.
Two external connection terminals, two coupling capacitors, and one variable resistor are used. Among these, external connection terminal t1
If the number can be reduced, it can be expected that the cost will be reduced accordingly. Furthermore, if it can be used for other circuit purposes, it becomes possible to increase other circuit functions. Furthermore, circuit parts such as coupling capacitors? It can also be reduced.

However, in the conventional O/U gain adjustment circuit as described above, the IC
It is impossible to follow the technological trends that accompany the change in technology.

Therefore, the main purpose of the present invention is to adjust the gain by reducing the external connection terminals when forming a conductor integrated circuit.
:・′:1 The purpose is to provide a circuit r.

Next, an embodiment of the gain a141 circuit using the kJIil of the present invention will be described with reference to FIG. Although the semiconductor integrated circuit IC has multiple functions, only the main parts are shown in FIG. 2 for the sake of explanation.

First, the circuit configuration will be described.

Inside the IC, there is a configuration ζn including a first operational amplifier OP, a voltage-current converter 1, and a second operational amplifier OP2. The non-inverting input terminal of the first operational amplifier OP is connected to a human input signal vi via the coupling capacitor 010% terminal. may be supplied from other circuits within the IC without being limited thereto.

Voltage-current converter (hereinafter referred to as ■-■ converter).

)1 is two constant current circuits O8,, as2.4 diodes DI%D! , Dl, Dl, four transistors Q
I% Consists of QB, Qj, and Q4. Then, the ■-operational converter IK is an operational amplifier o as a human input signal.
A voltage signal is supplied from the variable resistor VR, and its output signal is outputted as a current flowing through the variable resistor VR. Note that 1f: Resistor VR, is the output signal tW of the V-1 converter 1.
This is for converting it into an L voltage signal and supplying it to the second operational amplifier OP3 which operates as a voltage amplifier. Also, 2
The positive power supply voltage is 10 V at the terminal. 0 is supplied, and the negative power supply voltage -■ is supplied to the 3rd terminal. 0 is supplied.

Next, we will discuss the circuit operation when the human power voltage 1n is positive.

In this case, the voltage level at the output terminal of the operational amplifier op becomes positive. Therefore, the 7 node and cathode voltages of diode DI rise together, which causes transistor Q
Voltage VB], 1 or 1 is supplied to l.

Then, the base current xi flows from the constant current circuit O8 to the transistor Q1, and this transistor Q1 is turned on. As a result, the emitter voltages of transistors Q and l, that is, the voltage level at point A in Figure 2, rise, and the voltage generated by resistor R1 is applied to the inverting input terminal (-) of operational amplifier op.
will be returned to. 100% negative nulling is applied from the cutting point to the inverting input terminal (-) of the operational amplifier op, and the operational amplifier opl, diodes D, , D, ) transistor Q1
+ Q, resistance R, α Voltage follower operation with voltage gain 1. Therefore, in response to the human input signal voltage V, nVc, the collector-emitter path of the transistor QI or Q, the current L A n flowing through the resistance R1 at point A.
V t n/R1.

On the other hand, as the voltage level at the output end of the amplifier OF becomes positive, the base-emitter voltage vBll12 is no longer supplied to the transistor Q.

Therefore, transistor Q! is not in an off state, and transistor Q4 is also in an off state.

Then, by turning on the transistor Q2, the transistor Q2 turns off, and the voltage is 10V. o II
Source → Transistor Q3 → 4th terminal → Variable resistor VRt → Earth line +[Current IB flows through the flow path. The amount of current IB changes in response to the voltage level of human input signal 1n. Therefore, current mirror D3 * QB
If + D4 + Q4 is equal to reciprocal and Lfh characteristic is n, then F = F8, then the voltage level of terminal 94, in other words, the human power voltage of the second operational amplifier OF, tvX and Tn, is vX =vRIX1B=VR1·v1n/RI is determined. The human power voltage Vx is amplified by the operational amplifier OP2, and the degree of amplification is determined by the ratio of the resistors R1 and R3. Then, an output signal V of positive polarity is output from the output terminal of the operational amplifier op. ut is obtained.

Next, the circuit operation when the input signal V 1 n has negative polarity will be described.

In this case, the voltage level at the output terminal of operational amplifier OP becomes negative polarity. Therefore, the γ node and cathode voltages of diode D2 are lowered together, pace voltage vBE□ is supplied to transistor Q1, and transistor 0.2 is turned on. At the same time, the transistor Q1 turns off, so the earth line resistance R, → the emitter-collector path of the transistor Q, 2 → the diode D4 →
-V. owL source [stream flows]. As a result, the voltage level at point A decreases, and this voltage is generated across resistor R and fed back to the non-inverting input terminal of operational amplifier op.

- "mxmsiop" 0 output: By becoming positive polarity, transistor Q = 1% Q3 is turned off. However, since transistors Q and 4 are turned on, the ground Line → variable resistor VR, → 4-
? + terminal → collector-emitter path of transistor Q4 → -V. . wr, N, flows to the power supply. And Vx=
=VR,X As is clear from the IB formula, the voltage sending level of voltage vx becomes negative polarity. Therefore, an output signal V is generated from the output terminal of the operational amplifier OP2 in response to the negative voltage level of the human input signal V111. ut is obtained.

In the gain adjustment circuit operating as described above, it should be noted that the zero cross position of voltage Vg is equal to the voltage level of the ground line.

This is a power supply voltage of 10V. This is clear from the fact that the absolute values of 0% -voo are equal and the base voltages V□ when each transistor Q1'-Q4 operates in the on state are approximately equal. Furthermore, since the characteristics of each transistor QIXQ4 are the same, the absolute values of the variable resistors VR,'Q current and I[current are equal, and only the one changes. Therefore,
Sending pressure Vxn, zero position: 11111° position is +V. 0% "6o" is in the middle of the source, that is, at the same level as the ground line, and corresponds to the rolling level of the human power signal Vt.For this reason, the capacitor for cutting the DC component t becomes 0%. Furthermore, since a change in the resistance value of the resistor VR, which is connected to the ground line, directly results in a change in the voltage Vx, there is no need to derive a voltage signal from the movable terminal of the variable resistor VR. Only one external connection terminal is required for vRI, and the number of external connection terminals for connecting movable terminals can be reduced.

In the above-mentioned embodiment, the human input signal v1n is an audio signal, but is not limited to this, and may be a high frequency signal, and even a pulse signal may be used. As described above in the invention, when it is made into a semiconductor integrated circuit, the number of external connection terminals can be reduced, so the semiconductor substrate can be made smaller and the production cost can be reduced by a large amount. Furthermore, since the number of external circuit components can be limited, it is possible to reduce the number of man-hours required for pouring during assembly.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional gain adjustment circuit. FIG. 2 is a circuit diagram of a gain V@ adjustment circuit showing an embodiment of the present invention. Engineering 0...Semiconductor integrated circuit, OPl, O20...Operation amplifier, VR,...Variable resistor, Qi-Qi...Transistor, Dl to D4...Diode, l...
Voltage-to-current converter, vi. ...Human signal, Vout
...W force signal.

Claims (1)

[Claims] 1. A voltage-current converter that changes the current value of the output current in response to changes in the voltage level of the human input signal, and the voltage -1!
a load circuit that is connected to the output terminal of the current converter, changes the current direction in response to the polarity of the input signal, and obtains a voltage signal responsive to the change in current; and a voltage that amplifies the voltage signal. 1. A gain adjustment circuit comprising: an amplifier; and an output signal corresponding to the voltage level of the human input signal obtained from the voltage amplifier.