JPS5884513A - Gain controlling amplifier - Google Patents

Abstract

PURPOSE:To obtain a gain controlling amplifier with very little distortion, by inserting a distortion cancelling circuit consisting of a semiconductor rectifier in a path of an amplifier signal having a variable current source changing a common emitter current of transistors (TRs) depending on a control voltage. CONSTITUTION:In a distortion cancelling circuit 2, a DC blocking capacitor (C) 18a and a diode (D) 14a are inserted in series between a signal input terminal 15 and a resistor (R) 16 and in parallel with them, a DC blocking C18b and D14b are inserted in series. A connecting point between the C18a and the D14a is connected to a positive power supply 9 via an R19a and a variable R20a. Further, a connecting point between the C18b and the D14b is connected to a negative power supply terminal 6 via an R19b and a variable registor 20b. In a variable gain amplifier 1, the emitter of TRs 3, 4 is connected in common via Ds 21, 22 and to the terminal 6 via a TR23 and an R24. A part consisting of the TR23 and R24 and a part consisting of a TR25 and an R26 constitute a current mirror circuit. Thus, the distortion in the circuit 1 can be cancelled at the circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain control amplifier whose gain can vary linearly in response to a gain control signal such as a control voltage.

This type of gain control amplifier is generally used as a gain control amplifier because its purpose is to change the gain. For this reason, this type of gain control layer 11Il device generally has the disadvantage of extremely high distortion (for example, the total harmonic distortion is on the order of Q/A), and is therefore used in the audio field where high fidelity is required. etc., it was inappropriate to use - as a child volume, etc. This invention was made in view of the above circumstances, and its purpose is to create a non-feedback configuration with extremely low distortion. The present invention provides a gain control amplifier W which can also be used as an electronic plume for audio equipment. In order to achieve this object, the gain control amplifier according to the present invention comprises differentially tagged transistors, a variable current source that varies in accordance with a control voltage, and a common construction of these transistors. A distortion canceling circuit consisting of at least l pairs of semiconductor rectifiers connected in parallel and in the current direction is inserted in the input signal path of the gain amplifying section to eliminate distortion in the variable gain amplifying section. This is so that the distortion T is canceled out by the distortion T.

Hereinafter, a detailed explanation will be given with reference to an embodiment of the IWJ surface. IIIWJ is a circuit diagram illustrating the basic configuration of the gain control amplifier according to this explanation in the case where the ks input signal is positive. In this figure, reference numeral 1 indicates a variable gain amplifier, and reference numeral 2 indicates a distortion canceling circuit. In the variable gain amplification ILL, 8.4 is a differential transistor, both of which are NPN (NPN) transistors. Both emitters of these transistors 8.4 are common! I
At the same time, the negative power terminal 6 (
The power supply voltage is set to -Vcc) ・The current of this cute current source 5! , change T in proportion to the control voltage Vc (gain control signal) □ applied to the first control terminal 5m. The collector of the transistor 8 is connected to the inverting input terminal of the operational amplifier 7, and is also connected to the positive power supply terminal 1 (the power supply voltage is +Vcc) via a resistor 8t-. The pace of the transistor number is grounded through the resistor 1Ort, and the collector of the transistor is connected to the non-inverting input terminal &: of the operational amplifier 7, and is also connected to the positive power supply terminal 9 through the resistor 11t.◎Operation amplifier 7 The non-inverting input terminal of the operational amplifier 7 is grounded through the resistor 12t, and connected to the signal output terminal 1B of the operational amplifier 7 through the feedback resistor 14. 11 consecutive.

In addition, in the distortion canceling circuit 8, l- is a diode (semiconductor rectifying element), and the 7 nodes of this diode 14 are connected to the signal input terminal 16&:, and the cathode of the diode 16 is connected to the ground via a resistor 16.17 in sequence. has been done.

and resistance 16. l? The connection point of is connected to the pace of the transistor 8.

Next, the operation of this gain control amplifier having the above configuration will be explained.

First, we will explain the operation of a 1% variable gain amplification.

Resistance 16 in Distortion Cancellation Circuit School now. l? The voltage IVa of the signal supplied from the connection point to the base of the sill resistor 80
, the voltage of the output signal obtained at the signal output terminal 1B [v@ and T]. Here, if the control voltage Vc is a certain value, and therefore the control voltage is constant, then the rate of change of 111 voltage o with respect to voltage VJI is 1T, that is, variable gain amplification 11 - gain Gi (here The characteristic curve of Gt=h) is 1
It will look like ttinaa in Figure 11. In this case, the gain q1 of the variable gain amplifier 1111 is the same as that of the transistor 8.
．． - due to the action of the voltage between each pace emitter, the voltage Va
It is a nonlinear characteristic that T0 decreases as T increases.
If the control voltage Vc is changed, the current I will change T, so the gain G will be the same as that of the nonlinear characteristic tube.
, IIJtm, as shown by broken line b (when voltage Vc increases) or broken line 11c (when voltage Vc decreases),
T changes linearly in accordance with the control voltage Vc.

Next, in the distortion canceling circuit 8, the forward resistance 1d of the diode 16 is equal to the diode t4 as shown in FIG.
When the forward voltage Vd of I increases T, it decreases T, so one voltage V
The rate of change of T with respect to the voltage Vi of the input signal of a, T, that is, the gain G of the distortion canceling circuit 8, t where electric == ' 7 >
The property of −m is ll! It will look like T shown in the bower diagram. T, that is, in this case, the gain G of the distortion canceling circuit 2! is diode 1
Due to the action of 4, a nonlinear characteristic is shown in which the voltage Vi increases as T increases, and this nonlinear characteristic has an inverse relationship to the nonlinear characteristic of the gain G1 in the variable gain amplification ml described above.

As the product of the above result 1 gain G and gain G! ! The overall gain q of this gain-controlled amplifier (where ""v'
The non-silver type 8 of the gain G and the non-silver type of the gain G of 1 cancel each other out, resulting in a linear form.Thus, according to the basic configuration of T shown in FIG. Although it is a feedback film, it is possible to realize a gain control amplifier tube with extremely low distortion.

Next, based on this basic configuration, a concrete circuit rtllllI&
The T shown in the figure corresponds to each part in Fig. 1 in this figure.
The same parts are given the same reference numerals.

In the distortion canceling circuit 2 shown in Fig. S1, a DC blocking capacitor 18m and a diode 14m are connected in series between the signal input terminal 15 and the resistor 16. Been! !
In parallel with this, there is a capacitor 18b for DC blocking and a diode 14b.
Resistor 16 @ is inserted in Tj [next 1 [column]. The connection point between the capacitor 18a and the diode 14m is connected to a resistor 1.
91% variable resistor Iaoat - positive power supply terminal 9 through sequential
The diode 1 is connected to the diodes 1 and 2 to provide an adjustable DC bias current. Furthermore, the connection point between the capacitor 18b and the diode 14b is connected to a resistor 19b.
, variable resistor 5 obt - are connected to the negative power supply terminal 6 in sequence, so that an adjustable DC bias current can be supplied to the diode 14b.

In this case, when the human power signal Vi is positive, the human power signal is given distortion characteristics by the diode 14a and is supplied to the base of the transistor 8 (at this time, the diode 14b becomes a non-conducting part), and the - universal power signal When v is negative, the power signal is applied to the diode 14b&: Therefore, the distortion characteristic is given by the diode 14m, 14b.
A DC bias current is supplied to these UJ diodes 1481 and 14b using a variable resistor mwoaa"aobrt.
It is possible to set the optimum state to cancel the distortion of the variable gain amplification Thl by changing the transistor 8.
Each emitter of 4 is connected to a common transistor 8B and a resistor 24 through diodes 21-1 to zl-, diodes 22-21 to 2z-, and 1 diode-Fl, respectively.
The part consisting of the NPN transistor 25 and the emitter resistor 26 of the transistor 85 constitutes a current circuit, and the transistor 25 in this current circuit has a variable resistance 1'! ? , resistors 28 to 80, and a PNPF transistor 81. Two constant currents I corresponding to one control voltage Vc are supplied from a variable constant current circuit including resistors 28 to 80 and a PNPF transistor 81.

According to this specific circuit, when the input signal supplied to the signal input terminal 16 is amplified with a gain corresponding to the control voltage VC applied to the II control input terminal 51 and outputted from the signal output terminal 18, The distortion generated in the distortion canceling circuit 2 can cancel out the distortion generated in the variable gain increaser 11i&l.

As is clear from the above description, the gain control amplifier according to the present invention includes differentially configured transistors and a differentially configured transistor whose common emitter current of these transistors is changed in accordance with a gain control signal. In the path of the input signal applied between both paces, the current direction [l
l&: Then at least ! inserted in parallel with #! A distortion canceling circuit having a pair of semiconductor rectifying elements is provided, and the output is taken out from the collector side of the differential II transistor, so that the distortion of the variable gain amplifier can be canceled. This is offset by the distortion of the circuit, making it possible to realize a gain control/control amplifier with extremely low distortion. !
The gain control amplifier according to this invention has a non-feedback S configuration and has a simple circuit configuration, so it has the advantage of being able to change the gain extremely efficiently and being inexpensive. It is suitable as an electronic volume for use.

[Brief explanation of the drawing]

7(2) Basic configuration of the gain control layer III device according to the present invention [Circuit diagram shown in FIG. FIG. 4c is a characteristic diagram showing the gain change of the distortion canceling circuit 2 in the basic configuration. 1... Variable gain amplifier, 8... Distortion canceling circuit, 8.4... Differentially configured transistor, 5... Variable current source.

Claims (1)

[Claims] Variable gain amplification comprising transistors with a differential structure and a variable current source that changes the common current of these transistors in accordance with a gain control signal: S
In the path of the input signal applied between the bases of the TT differential 11I transistor, there are at least l pairs of semiconductor rectifying elements inserted in parallel with current directions opposite to each other. A gain control amplifier comprising a distortion canceling circuit and configured to take out an output i from the collector of the transistor formed by the differential transistor.