JPH02301307A - Gain switching circuit - Google Patents

Abstract

PURPOSE:To attain the gain switching without changing a gain control input voltage by varying a current quantity of a current source circuit being a component of a gain control circuit depending on the gain switching input. CONSTITUTION:A collector of a transistor(TR) Q12 of a 4th current source comprising of the TR Q12, a resistor R6 and a reference voltage source VR1 being the same constitution as a 1st current source comprising a TR Q1, a resistor R1 and the reference voltage source VR1 connects to a collector of the TR Q1. A collector of a Tr Q13 of a 5th current source comprising of the TR Q13, a resistor R7 and the reference voltage source VR1 to a collector of a TR Q3. Moreover, collectors of TRs Q14, Q15 connect to a voltage Vcc and a bases connect to a gain switching voltage V3. Then the current of the current source circuit is varied with the gain switching input. Thus, the gain is changed without changing the gain control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gain switching circuit for a gain control circuit that performs gain control using a gain control input voltage.

(Conventional technology) A conventional gain control circuit is shown in FIG.

This circuit consists of a first current source consisting of an npnh transistor QU whose base voltage is determined by a reference voltage source Vat and a resistor R4 between its emitter and GND, a second current source consisting of Q□ and R3 having the same configuration as the current source, and Q3. There is a third current source consisting of R3, the collector of transistor Q1 is an npn transistor Q4 whose base is the signal input terminal.
and reference voltage power supply■. ■ Power the base and collector. . It is connected to the emitter of an npn transistor Q, which is Q.

Transistors Q and Q constitute a first operating circuit. The collector of transistor Q4 is based on the gain control voltage 1, and the collector is n
It is connected to the emitter of a pn transistor Q6 and an npn transistor Q7 based on a gain control voltage 2, transistors Q and Q7 forming a second operating circuit. Moreover, the collector of transistor Q2 is
Based on the gain control voltage 2, the collector is set to v
npn transistor Q with ccl as base, and npn transistor Q with gain control voltage l as its base.

is connected to the emitter of transistor Q.

and Q constitute a third operating circuit. The collectors of transistors Q7 and Q are common, and the emitters are connected to the resistor R.
4 and the collector and base of a pnp transistor Q1° connected to ycc through.

pn whose emitter is connected to vo through resistor R6
It is connected to the base of p-transistor Q4, and the transistor is connected to the base of transistor Q4. , Q, and □ constitute a first current mirror. The collector of transistor Q3 is connected to the collector and output terminal of transistor QU□.

Next, the operation of this circuit will be explained. The collector current of transistor Q1 determined by the first current source is the input signal V
l) The difference between l and vo is divided by the first actuating circuit into the collector current of transistor Q, which collector current is equal to the voltage V1. V
, is divided by the second operating circuit and becomes the collector current of transistor Q7.

On the other hand, the collector current of transistor Q, which is determined by the second current source, is divided by the third operating circuit due to the difference between the voltages V, , V, and becomes the collector current of transistor Q. The sum of the collector currents of transistors Q7 and Q is the sum of the collector currents of transistors Q1. .

The collector current of the transistor Q1x passes through the first current mirror consisting of Q41, and this current and the
The difference between the collector currents of transistor Q, which is determined by the current source of , is the output current I. ut yells.

(Problem to be solved by the invention) I for vllI. The gain of ut is determined by the voltage at gain control terminals 1 and 2■1. (2) Since the circuit configuration is determined by the potential difference of 2, there is a problem that the gain can only be set using the setting method described above.

The present invention solves these problems.

The purpose of this is to widen the set gain width by switching the gain determined by the potential difference between the voltages V□t and V2 using a gain switching circuit.

(Means for Solving Problem i) In order to solve this problem, the present invention provides a method for controlling the amount of current of a current source circuit constituting a gain control circuit that adjusts the gain using a gain control input voltage using a gain switching input. This makes it possible to switch the gain without changing the gain control input voltage.

(Function) This configuration makes it possible to switch the gain using the gain switching circuit without changing the gain control voltage, and solves the problem that the gain setting range is narrow because the gain is set only by the gain control voltage. Ru.

(Embodiment) An embodiment of the present invention will be described with reference to the circuit diagram shown in FIG. This circuit diagram shows a transistor Q1m and a resistor R, which have the same configuration as the first current source consisting of a transistor Q and a resistor R□ and a reference voltage source vlll in the conventional example shown in FIG.
The collector of a transistor Q□2 of a fourth current source consisting of a high reference voltage source v,1 is connected to the collector of a transistor Q, and a transistor Q□2 having the same configuration as the current source is connected. The transistor Q of the fifth current source consists of a resistor R2° and a reference voltage 1 [V m z. Connect the collector of the transistor Q3 to the collector of the npn transistor 014 j Q
The collector of IC is connected to V, the base of IC is connected to gain switching voltage V1, transistor Q1. The emitter of transistor Q
The emitter of the transistor Qhs is connected to the emitter of the transistor Qhs.

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

■□ is the base voltage. Transistor Q i IQ,
, Q3. Q□z, Qta and their respective emitters G
The gain switching voltage ■ is where the first to fifth current source currents consisting of the N-to-ND resistance are denoted by I and I, respectively.

voltage is low level (transistor Q, 4. Q, ,
is turned off, and the fourth transistor consisting of transistors Q x z + Q x a is turned off. current 11 and I4 when the fifth current source is on)
The sum is divided by a first differential circuit consisting of transistors Q and Q, producing a collector current of transistor Q. As a result of the division, if the sum of the current amount and I4 is A%, the collector current of the transistor Q is A(I
(0≦A≦100), then this current is divided by a second differential circuit consisting of transistors Q, , Q, and becomes the collector current of transistor Q7.

Gain control voltage V.

If the collector current of transistor Q becomes B% due to the difference ΔV between
), on the other hand, the collector current ■2 of transistor Q2 is divided by the third differential circuit consisting of transistors Q, , Q, and becomes the collector current of transistor Q. Since the zero division ratio is determined by ΔV, the collector current of transistor Q, The current is (1-B)I.

The sum of the collector currents of the transistor Q7 and the collector current of the transistor Q is the transistor Q.

, QU□, R4, and Rs, the collector current of transistor Q11 becomes A.
B(1,+I4)+(1-B)1. It is. (Assuming the mirror ratio is 1), the output current is the current obtained by subtracting the sum of I and I from this current. , Therefore, the output current when ■ is low level. u? lLl is expressed by the following formula.

Iouy+L+=AB(I,+I4)+(1-B)Iz
-(I3+L)...■ Next, when ■ is at a high level, the transistor Q14
y Q X S turns on, transistor Q□zeQ1
3 turns off, 1. =O11, =O, and the output current I. uf+. is the following formula.

Iouttll)=ABIx+(IB)I, -I3-
...The gain control voltage is v3 from the 0th order ■ and ■ formulas.
If the 0-level and V3 high level are equal, I
The gain with respect to the input voltage V0 of Out is determined by the following equations at (2), low level, and (3) high level, respectively, due to changes in the division ratio A of the first differential circuit.

From these two equations, the process for changing VIN. , the change in
You can see the difference between vlo-level and ■3 high level.

As described above, even when the gain control voltages are equal, the gain can be changed by switching the gain switching voltage V.

(Effects of the Invention) As described above, according to the present invention, since the gain switching circuit is used, it is possible to obtain the effect of changing the gain without changing the gain control voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. vcc...power supply voltage, Q1-Qzs...transistor, R1-R7...resistance, vllll, v1
! ...Reference voltage source, VIN...Input terminal. Engineering. 1... Output terminal, ■... Gain control voltage of gain control terminal 1. ■,...gain control voltage of gain control terminal 2, ■,...gain switching voltage of gain switching terminal. Fig. 1 VRl-VR2--Ant pressure source Key-in control electric voltage tvIN----person"1,000V3-
'f'<'/a'y t+f '4'AIW
ft10U? ---One output terminal

Claims (1)

[Claims] By changing the amount of current in the current source circuit that makes up the gain control circuit that adjusts the gain using the gain control input voltage using the gain switching input, it is possible to switch the gain without changing the gain control input voltage. gain switching circuit.