JPS6338315A - Gain control circuit - Google Patents

Abstract

PURPOSE:To secure the margin of the bias voltage by providing two current sources to give the differential control to the currents of both current sources according to a control signal and therefore increasing a dynamic range. CONSTITUTION:A pair of currents having the differential changes are supplied to a pair of diodes and converted into a pair of differential voltages. These voltages are supplied to a pair of input terminals T1 and T2 of a differential amplifier 1 set at the next stage. A pair of output terminals T3 and T4 of differential amplifiers 3 and 5 are connected in parallel to a pair of output terminals T3 and T4 of the amplifier 1. The constant current sources of those amplifiers 1, 3 and 5 are formed with output-side transistors Q7, Q8, Q13 and Q14 respectively. Then a pair of control currents having differential changes are supplied to a pair of current mirror circuits 12 and 13. Thus an output undergone the gain control is obtained from a differential amplifier. In such a way, a dynamic range is increased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a gain control circuit.

[4) Summary of the Invention] The present invention expands the dynamic range by reducing the number of transistors stacked in series in a gain control circuit by reducing the number of transistors stacked in series with respect to the source voltage 4). It is.

[Conventional technology]

A circuit like the one shown in FIG. 2 has been considered as a ÷11 control circuit.

That is, in the figure, Ql and Q2 are transistors (diodes') for current-to-electrical ratio conversion, and Q4.

Q4 is a differentially connected 1-transistor.

therefore, 1+ lx+1i 12-1x-1i 1]: Input terminal of terminal T1 ■2: Input terminal of terminal T2 1χ: DC component ]1; AC minute 13=Iy-T.

+4-1y 1-1゜ ■3: Output -diik of terminal "1"].

■4 Output current Iy of double-width single-child T4: Constant current source (1/2 (DC portion) of the constant current of Uy) Ii: If the total current is taken, the current gain Ai of this circuit is 81-To /1
i = Iy/lx (if buttocks) ... (i
), and this circuit becomes tilJ< as a current amplifier with a current gain Ai defined by the equation.

At this time, if we change the magnitude of the current 1y, we get
Since the current gain Ai changes from equation (i), as a result, this circuit functions as a gain control circuit.

Figure 3 shows an example of its application, with transistors Q1,
~Q13 constitutes a differential amplifier (1), and the terminal T1
．． The input signal of T2 is changed to a current If, +2 by the amplifier (1).
and (J( is supplied to the transistor (G+, Q*).

Further, the transistors Q3 to Q9 provide a constant +17. balance
r+l 1ffi t2+ is configured and a control voltage is supplied to terminal T5.

Therefore, currents 1+ and 12 flow through the transistors Q1 and Q2 due to the human input signal at the terminal T1+ 72, and as a result, a current of 13°■→ flows through the transistors Q3' and Q4, and the current 13+I4 flows through the resistors R3 and R4.
It is converted into a salt 17 and taken out to the terminal 'r3'r4. At this time, since the transistor Q7 corresponds to the constant current source Qy, the gain changes according to the control voltage of the terminal T5.

Also, at this time, transistor Q7 and transistor Q8
Since the collector current changes differentially, the DC component of the current flowing through the resistors R3+R4 is constant, and therefore the DC level of the terminals T3 and T is controlled by the control
remains constant regardless of

(Reference: Japanese Patent Publication No. 48-20932) [Problem to be solved by the invention] However, in the circuit shown in Fig. 3, the power supply +V
Between CC2 and ground, 1'l resistors R3 and R4, signal transistors Q3 to Q6, current control transistors Qv, (le, and constant current source transistor Q) are connected between CC2 and ground.
9 are connected in series, so if the power supply voltage +V CC2 is (1ζ), as in a battery-operated VTR with an integrated camera, the dynamic range of the output signal 1 - becomes small. Also, there is no margin for the bias of each transistor.

This invention attempts to solve these problems.

[Means for solving the problem] Therefore, in this invention, two current sources are provided,
Control the current of this current source (differentially control according to No. 8).

[Effect]

', f& The number of 1·-non transistors connected in series between the source and ground is reduced.

〔Example〕

In Figure 1, a common emitter transistor (, 11
3, (:l Transistor Qu with 14 as a constant current source.

A differential amplifier (11 is configured by Q+=, and the base of the transistor Q o + Q 12 is the input terminal T 1+
A diode-connected transistor Q1. Q2 is connected.

Further, a differential amplifier (3) is constituted by transistors Q3 + Q4 using a common emitter transistor Q7 as a constant current source, and transistors Q3. The base of Q4 is connected to the emitters of transistors Ql and Q2, and the base of transistors Q3. (The collector of L is connected to the output terminal T], T4, and is connected to the power supply terminal T12 through the resistor R3゜R4.
connected to.

Furthermore, the transistor Q5+Qe+08 similarly constitutes a differential amplifier (5), and the transistor Qs
, Q6 are supplied with a constant bias voltage VR to their bases, and their collectors are connected to resistors Rq, R, +.

Further, the voltage terminal TI3 is set as the reference voltage point A1), and the transistor Q21. A differential amplifier (+1) is constructed by using transistor 122 as a constant current source, Q24, and emitter 1 (old 1 (anti-z:) 1 x 1).
The base of transistor Q 231 Q 24 is the control vehicle j
It is connected to the input terminal 'l''6°T6 of L, and its 2l collector is connected to the collector of transistor Q26.Q2G.

In this case, a current mirror circuit (12) is constructed in which the transistor Q2 is used as the input terminal, the transistors Qe and Ql4 are used as the output side, the transistor 127 is used for bias, and the ground is used as the reference potential point,
Transistor Q26. Qv, Qll (Yu2
Similarly, a current mirror circuit is formed by 8.

Furthermore, the transistor Q]1 is connected to the input terminal, and the transistor Q
21. A current mirror circuit (14) is constructed with Q22 on the output side, transistor Q (2) for bias, and power supply terminal TI3 as a reference potential point. A constant current I is supplied.

According to such a configuration, transistor Q3. .

Since Q2+ and Q22 form a current mirror circuit (14), transistors Q21 . The collector of Q22 has a current of 1. I flows. Since the transistors QH and Q22 are also constant current sources for the differential amplifier (II), the currents ■ and ■ are supplied to the terminals T5. According to the T'60 control voltage, the current is divided into 123+124 and flows through the ζtransistor Q211, (124).

However, 12] ++24-21 ... (i
i >.

And this current 1? q, l>4 is transistor Q 2
．． , 026 and 4), the transistor Q2
5°Qll and Q26. Ql3 is a Karen I/mirror circuit (12).

(''3), so the transistor Q13゜Q
l4 has a current of 124. I2i flows, and at this time, l-runsistor QI3. Since Ql4 is a constant current source of the operational amplifier (1), the constant current for transistors Qll and Ql2 is 11 + + 24, st (also, constant current 2), and the current flowing through transistors Q1 and Q2 is I1 and T2.
The DC component is 1x, 1xL11, l x -1... (iii).

In addition, the transistors Q2s, Cgo8 and Q2G,
Since Ql also constitutes the current mirror circuits (12) and (13), a current of 124° + 23 flows through the transistors (Yv, Qg).Then, ζ, the transistor Qv
Current 124 of transistor Q3. The current flowing through Q4 is divided into three equal parts +3. Since the DC component of +4 is +y, +y, ly = 124/2 ・=・(iv).

Therefore, the current gain ^1 due to the transistor (U1.Q2 and differential amplifier (3) is (i), (i
ii).

From formula (iv), ^1=Iy/lχ = 124/ (21) (iiη)...
...(V). And in this case, terminal T5
, according to the control voltage of ``l'e °C1tX current +24
Since the magnitude of changes 4-, the control car is set to 1)-.
, C, current interest 11! Every time ^i changes.

Also, if the value of the resistor connected to the emitter of transistor Qo + Q12 is shifted from R, the terminal Ts.

T2 and terminal T3. The voltage gain ^ν between T4 is +2
3 + I 24 R + R. In this case, terminal 'F5. Current 1 due to control voltage of 'I''e
24 changes, and ν changes to the voltage gain.

Furthermore, in the current mirror circuit (12), a current flows through the transistor QIT! 23 flows, but this current 12
3 is divided into three equal parts by transistor Qe + Q6, and current +21/2°12 is applied to transistors Q5 and QF.
3/2 flows, and this current further increases to 11 (resistor Rs.

Flows into the blue sky.

Therefore, °ζ, the currents flowing through resistors R11 and R4 are respectively ly ++ 23/2 to 124/2 + 12
3/2-■. In other words, a constant 11'1 current 1.1 determined by the (51 constant current source Q33) flows through the resistor R3, +?+.

Therefore, terminal T3. 'r4 DC level is terminal T
r7. regardless of the control weight of s + T6. is equal to and constant.

〔Effect of the invention〕

Thus, according to the present invention, it is possible to perform gain control, but in this case, especially according to the present invention, the power supply voltage +
Since VC (ζ resistor R for :2), R4, transistors 03 to Q, and transistors Q? and Qa are connected, compared to the circuit in Fig. 3, the number of transistors 11
In addition to being able to expand the dynamic range,
There is also room for pie-female weight.

Furthermore, the dynamic range of the differential amplifier (11) becomes the control range of the gain ^ν, and the control of VC-V+s j I 17Vr, , Vs: 1 r-'r, , , T,
It can be controlled over the range of 0.00000000000 0.0000000000 0.000000000 0.0000000000 0.0000000000
When R21<VC, the gain is 0 times.

Also, when I2x-124 due to the control voltage, 1
24-1, the voltage gain ^V is determined only by the resistance ratio. In other words, there is no variation in the reference voltage sum mAν.

Furthermore, each time a differential amplifier (11, (31, (51) corresponding to differential amplifier) is additionally connected to the differential amplifier (11) and current mirror circuits (12), (13), a common control voltage Multiple gain controls can be performed simultaneously and with equal characteristics.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of an example of the present invention, and FIGS. 2 and 13 are diagrams for explaining the same. fl, l, +31, (51, (1, 1) is a differential amplifier, (12) to (14) are current mirror circuits. Commissioner of the Patent Office Kuro 111 Akira J
218) Sony Corporation Representative Director Ohga; 311Aj1 4, Agent (1) In the statement, page 6, lines 2 and 9 (total 2 places)
Delete "grounded emitter". (2) Same, page 7, line 10 and 5 to 4 lines from the bottom (total 2
Part) Correct "bias" to "buffer". (3) Correct the numerator "R3" in the formula in lines 4 and 5 of page 10 (total of 2 locations) to rR3+RqJ. (4) Same, page 12, lines 5 to 9, ``Control voltage...further'' is deleted. that's all

Claims (1)

[Claims] A pair of differentially varying currents is supplied to a pair of diodes and converted into a pair of differential voltages, and this pair of differential voltages is applied to a differential amplifier in the next stage. one pair of input terminals, and one pair of output terminals of the above differential amplifier, one of the differential amplifiers.
A pair of output terminals are connected in parallel, and each constant current source of the differential amplifier and the other differential amplifier is configured by an output side transistor of a pair of current mirror circuits, and the pair of current mirror circuits is connected in parallel. 1 that changes differentially to
A gain control circuit configured to supply a pair of control currents to obtain a gain-controlled output from the differential amplifier.