JPS58161513A - Gain control amplifying circuit - Google Patents

Abstract

PURPOSE:To linearize the control voltage-gain characterisics, by inserting a transistor to a diode and supplying the input signal voltage given from an input signal source to the emitter of a current source transistor. CONSTITUTION:It is possible to set the DC voltage of a signal output terminal 11 at a fixed level owing to the function of a dummy circuit 22 despite variations of control voltage VC since diodes D an D' are inserted to the emitters of transistors TRQ2 and Q2' having a base common with each other. While input signal voltage ei is converted into a signal current I0 as shown by i0=ei/Ri if signal current i0 flowing to a constant current source 21 from an input signal source 14 via an input resistance Ri is much less than the current IO of a constant current source 21. Then the signal current i0 flows to TRQ1 and Q2 with a shunt ratio which is decided by the control voltage VC, and output signal voltage e0 is generated by a signal current i1 which flows to a load resistance RL. The gain control characteristics of this circuit depend approximately on a linear equation of the current I1 of the TRQ1 and becomes linear.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a transistor amplifier circuit, and particularly to a gain control amplifier circuit with a variable shunt ratio Wi.

[Technical background of the invention and its problems]

A conventional example of this type of variable shunt ratio gain control amplifier circuit is shown in FIG. That is, they are NPN type transistors forming a Qt and QsU differential pair, and their emitters are connected together.

The collector of one transistor Q1 is connected to the signal output terminal 11 and is also connected to the power supply element B via the load resistor RL, and the collector of the other transistor Q1 is directly connected to the power supply element B. There is. Further, a variable voltage wave control power source 1j is connected between the bases of the transistors Qs and Q3 of the differential pair.

On the other hand, QI is, for example, an NPN type transistor for a current source, and its collector is connected to the differential pair transistor/zoster Q>
The emitter of the transistor Q3 is connected to the dummy resistor R of aQz, and the emitter of the transistor Q3 is grounded through the dummy resistor R.

IJ is a bias power supply and is connected to the pace of the transistor Qs. 14 is an input signal source, 15 is its internal resistance, and 16 is a rounded coupling capacitor that supplies the input signal from the input signal source 14 to the pace of the transistor Qs.

Furthermore, 11 is a dummy circuit, which includes differential pair transistors Q, / and Q, /, current source transistor Q
I'% Dummy consists of a resistor R11 and a bias power supply 1s'. The differential pair transistor Q1'.

Each collector of Qs' is correspondingly connected to each collector of the differential pair transistor Ql=Q1, t*) The bases of transistors Q1 and Qt' are connected together, and the transistors Q3 and Q, 10 bases are connected together. Comrades are connected. Note that the voltage of the bias power supply 13 and the voltage of the bias power supply 13' are equal, and the dummy resistors RI and lj are selected to have equal values.

Therefore, the voltage of the bias power supply IJ causes the transistor Q to
The DC current I of s is determined, and this current l is the control power supply 1
The shunt ratio (11:I) determined by the control voltage VC from 2
s) to the differential pair transistors Q1 and Qs. Note that the dummy circuit 11 operates in the same manner as this operation, and the DC voltage at the signal output terminal 11 is kept constant even if the control voltage ■c changes.

Now, when an input signal voltage e (is input from the input signal source 14), this signal voltage e1 is converted to a signal voltage f by the transistor Qs.
Transistors Q1 and Q with a shunt ratio ('l;ds) determined by this signal current control voltage
! An output signal voltage eo is generated by the signal current i1 flowing through the load resistor RL of one transistor Q1,
The magnitude of this signal voltage eo is 5lXRL.

Therefore, the signal current (all of 0 is transistor Qxt
When flowing, 4 ea =<6xRL =-XRL,
-...+-(S) In order to control the gain G of the above circuit, the transistor Q
The signal current flowing through the transistor Q1 (1 can be changed by the control voltage ■).Here, consider the gain control characteristics.
v112, and these differential voltages are expressed as Δv and 12, as follows.

1, +Il ”I...
- Since (4) is satisfied, the change in the current 11 with respect to the change in the p1 control voltage VcO depends on 1h (Io-It).

On the other hand, the output signal voltage e・ and the input signal voltage e (as described above, are respectively ee −4s
This is because it is. Then, the gain G is obtained from the above formula and the cutting allowance (6). That is, as can be seen from the above equation aυ, the gain G is the change in the current I of the transistor Q1 with respect to the change in the control voltage VC.
There was a drawback that the gain control characteristic changed according to the square of l, and the gain control characteristic became nonlinear as shown by the dotted line in FIG.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and provides a gain control amplifier circuit with a variable shunt ratio that can linearize the control voltage vs. gain characteristic.

[Summary of the invention]

That is, the present invention relates to the emitter of the transistor that is not for signal output among the differential pair transistors.

A diode is inserted on the opposite side, a load resistor is also inserted on the collector side of the transistor, and a diode is inserted on the emitter and rear side of the transistor whose bases are connected to each other in the dummy circuit. A common base transistor is used in the transistor current source circuit,
An input signal is supplied to the emitter side of this transistor. Therefore, the forward voltage drop of the diode affects the control voltage, and the gain control characteristics are linearized.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. I! The variable shunt ratio gain control amplifier circuit shown in FIG. 2 is different from the gain control amplifier circuit described above with reference to FIG. The input signal voltage e from the input signal source 14 is
The difference is that , is supplied to the emitter of the current source transistor Q3 through the coupling capacitor 16 and the input resistor Ri in series, and other things are the same, so the same parts in FIG. 2 as in FIG. The explanation will be omitted.

The diode D has an anode connected to the transistor Q!
is connected to the emitter of the transistor Q, and its cathode is connected to the emitter of the transistor Q
It is connected to the emitter of L and the collector of current source transistor Q3.

t7'E, the other diode V has its anode connected to the emitter of the transistor Q', and its cathode connected to the emitter of the transistor Q, / and the collector of the current source transistor Qs'. The load resistor RL' is connected between the collector connection point of the transistors Q and Qm' and the power supply 1B. In addition,
The currents l and yI6' of the constant current sources 21° and 21' are made equal to each other.

In the above configuration, since the diodes D and D' are inserted into the emitters of the transistors QsIQ', which have a common base, even if the control voltage vc changes, the dummy circuit 22 remains unchanged. By the following operation similar to the operation in the conventional example, the effect of making the DC voltage at the signal output terminal 11 constant can be obtained as in the conventional example.

On the other hand, if the signal current flowing from the input signal source 14 to the constant current source 21 via the input resistor R is sufficiently small compared to the current of the constant current source 21, the input signal voltage e1 will be as shown in the following equation. It is converted into a signal current 46.

Then, the transistors Qt and Qx are controlled at the shunt ratio (jx; jx) determined by the signal current (・ is the control voltage
The signal current (1) flowing through the load resistor RL generates an output signal voltage e.

Next, the gain control characteristics of the above circuit will be considered.

When the forward voltage drop of diode D is expressed as VD, Vc
” Vmml −VD −Vmm2 =...(
131 is established. Here, the same current flows through the emitters of diode D and transistor Q3! Since the snow is flowing, ■ゎ＝V□２ ・・・・・・α荀(However, %
Il:) saturation voltage fi) of the transistor is established.

This is because II +I, =Io, , , , αe. On the other hand, the gain G is obtained according to the reduction 〇□, and is obtained from the above equation α Yu and the creation Qe. That is, as can be seen from the above equation, the gain control characteristic approximately depends on the linear equation of the current factor 1 of the transistor Q1, and becomes a KIII type as shown by the solid line in FIG.

It should be noted that the present invention is not limited to the above-mentioned embodiment, and it is sufficient to provide a current source circuit using pace-grounded current source transistors as the current source transistor Q3 and the constant current source 21. Also in the dummy circuit 22, a current source circuit may be provided as the current source transistor Qs' and the constant current source 21'.

〔Effect of the invention〕

As described above, according to the gain control amplifier circuit of the present invention, the control voltage vs. gain characteristic can be linearized, so by digitally varying the control voltage in a digital device, a digital control amplifier circuit with linear input/output characteristics can be created. It has the advantage of widening the scope of application, such as being able to realize the following.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional gain control amplifier circuit, Figure 2 is a circuit diagram showing an embodiment of the gain control amplifier circuit according to the present invention, and Figure 3 shows the control characteristics of Figures 2 and 1. FIG. Qs −Qs e Qx′〜Qs”=) Lanzosta,
DID'...Diode, RLIRL'...Load resistance, 11...Signal output terminal, 12...Control power supply, 1
3... Bias power supply, 14... Input signal source, 21.
21'... constant current source, 22... dummy circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (2)

[Claims] (1) A signal output transistor Qr and a transistor Q that forms a differential pair with this transistor Ql! A diode D is inserted and connected in the forward direction between the emitter of the transistor Q3 and the emitter of the transistor Q1, and a diode D is connected between the connection point between the diode D and the transistor Q1 and the ground terminal. A current source circuit using a grounded current source transistor Qs, load resistors R5 and RL' connected to a power supply corresponding to the respective collectors of the transistors Q1 and Q3, and An input signal is supplied to a variable voltage control power supply 12 inserted and connected between the paces, a dummy circuit 22 that stabilizes the DC voltage of the collector of the transistor Q1, and the emitter and rear sides of the transistor Q3 of the current source circuit. 1. A gain control amplifier circuit comprising means for. (2) The dummy circuit 22 forms a differential pair with a transistor Q,1 whose collector is connected to the collector of the transistor Q3 and whose pace is connected to the pace of the transistor Q1, and the transistor Qs. a transistor Q' whose collector is connected to the collector of and whose pace is connected to the pace of the transistor Qs;
and a diode V inserted and connected in the forward direction between the emitter of this transistor Q,'llD and the emitter of the transistor 91', and this diode is connected to the emitter of the transistor Q,1. 2. The gain control amplifier circuit according to claim 1, further comprising a current source circuit connected between the point and the ground terminal.