JPH06152284A - Voltage control amplifier circuit - Google Patents

Abstract

PURPOSE:To enlarge the allowable range of an output potential compared with the conventional voltage control amplifier circuit by changing a gain by means of transistors which constitute a differential amplifier circuit amplifying an input signal and another differential amplipier circuit constituted of transistors of reverse junction. CONSTITUTION:The circuit is provided with a resistance RE connecting mutual emitters by impressing an input signal voltage vi to the base of transistors TRQ 1 and Q2 and a 1st differential amplifier circuit where constant current sources I1 and I2 are connected to the respective emitters. Then, a 2nd differential amplifier circuit is formed by connecting TRQ 3 and Q4 emitters and connecting them to a constant current source I3. A 3rd differential amplifier circuit is formed by connecting TRQ5 and Q6 emitters and connecting them to a constant current source I4. In this case, the collector of the TRQ2 is commonly connected to the emitters of TRQs 5 and 6. The bases of TRQ3 and Q6 are connected to a control terminal. The bases of the TRQ4 and Q5 are connected to the control terminal. The collectors of the TRQ4 and Q6 are outputted through a resistance RL.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled amplifier circuit, and more particularly to a voltage controlled amplifier circuit used in an AGC amplifier circuit or the like.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional voltage control amplifier circuit includes a transistor Q1 for amplifying an input signal source vi.
It is composed of a first differential amplifier circuit composed of Q2 and second and third differential amplifier circuits composed of transistors Q3, Q4 and transistors Q5, Q6 whose output current is variable by an external control terminal T1. To be done.

The first differential amplifier circuit has a resistor RE and constant current sources I1 and I2. A constant voltage source V1 is added to the input signal source vi. The second differential amplifier circuit is npn
A resistor RL is added to the collector of the transistor Q3. A constant current source I3 is added to the third differential amplifier circuit. As these power supplies, a constant voltage source V2 is prepared.

Next, the operation of the circuit shown in FIG. 3 will be described.
The signal vi input to the first differential amplifier circuit composed of the transistors Q1 and Q2, the emitter resistance RE, and the constant current sources I1 and I2 is expressed by the following equation as collector currents IC1 and IC2 of the transistors Q1 and Q2. Represented by. The current value of the constant current sources I1 and I2 is I0.

[0005]

The collector current IC of this transistor Q2
2 is connected to the common emitters of the transistors Q3 and Q4, and the base potentials of the transistors Q3 and Q4 are controlled by the external control terminal T1. Now, the difference between the base voltages of the transistors Q3 and Q4 (VB3-V
When B4) is VA, the collector current IC3 of the transistor Q3 is as shown in the following equation.

[0007]

By substituting the above equation into the above equation (3), the following equation (4) is obtained.

[0009]

Since the base voltage difference (VB6-VB5) between the transistors Q5 and Q6 is also VA, the collector current IC5 of the transistor Q5 is given by the following equation (5).

[0011]

Here, the current of the constant current source I3 is set to I0. The current flowing through the load resistance RL is (IC3 + IC5)
Therefore, the output voltage v0 is expressed by the following equation.

[0013]

Therefore, the output DC voltage is (I0 × R
In L), the gain can be changed by the control voltage VA only for the AC component with a constant voltage regardless of the control voltage VA.

Now, consider the output amplitude with VCC = 5V. The base potentials of the transistors Q1 and Q2 are at least 2 of the base-emitter voltage VBE of the transistors when the constant current sources I1 and I2 are transistors.
Since more than twice is necessary, V1 = 2V is set. Next, considering the base potentials of the transistors Q3 to Q6, this voltage requires at least (VBE + input) amplitude for V1, so the voltage of the terminal T1 is set to 3V. Therefore, the output amplitude can be maximized from VCC = 5V to 2VPP obtained by subtracting the voltage 3V of the control terminal T1.

[0016]

In this conventional voltage control amplifier circuit, a transistor pair forming a differential amplifier circuit to which a signal is input and a transistor pair forming a differential amplifier circuit for varying the gain are provided. However, there was a problem that the amplitude of the output voltage was limited due to the vertical stacking. For example, if the power supply voltage is 5V, the maximum output amplitude is 2V.
I could only take PP.

An object of the present invention is to solve the above-mentioned problems and to provide a voltage control amplifier circuit capable of taking a large output amplitude.

[0018]

The structure of the present invention comprises: a first and a second transistor to which an input signal is applied to a base;
A first emitter resistance connecting the emitters of the first and second transistors to each other, and a first and second constant current sources connected to the emitters of the first and second transistors, respectively Of the differential amplifier circuit, the second differential amplifier circuit in which the emitters of the third and fourth transistors are connected to each other and to the third constant current source, and the emitters of the fifth and sixth transistors are connected to each other. And a third differential amplifier circuit connected to a fourth constant current source, wherein the collector of the second transistor has the fifth and fifth differential amplifier circuits.
Connected to the common connection point of the emitter of the sixth transistor,
The bases of the third and sixth transistors are commonly connected to form a first control terminal, and the bases of the fourth and fifth transistors are commonly connected to form a second control terminal. The collector of the sixth transistor is connected to the load resistor and the output terminal.

[0019]

The present invention will be described below with reference to the drawings. 1 is a circuit diagram showing a voltage controlled amplifier circuit according to a first embodiment of the present invention.

In this embodiment, in FIG. 1, an input signal vi biased with a constant voltage V1 is applied to a first differential amplifier circuit composed of transistors Q1 and Q2, emitter resistors RE, and constant current sources I1 and I2. The output of the first differential amplifier circuit, that is, the collector of the transistor Q2 is input, is connected to the common emitters of the fifth and sixth transistors that form the second differential amplifier circuit, and the constant current source I4.
Connected to. On the other hand, the input of the second differential amplifier circuit is connected to the control terminal T1 and also connected to the input of the third differential amplifier circuit to form a transistor Q3 that constitutes the third differential amplifier circuit. The common emitter of Q4 is a constant current source I
3 and the collector of the transistor Q4 and the collector of the sixth transistor are commonly connected to the load resistor RL and used as the output vo of the voltage control amplifier circuit. These circuits are biased by a constant voltage source V2.

Next, the operation will be described. The signal vi input to the first differential amplifier circuit composed of the transistors Q1 and Q2, the emitter resistance RE, and the constant current sources I1 and I2 is the collector current of the transistors Q1 and Q2, IC
1 and IC2 are represented by the following equation.

[0022]

However, the current value of the constant current sources I1 and I2 is I
Set to 0.

The collector of the transistor Q2 is connected to the common emitter of the transistors Q5 and Q6 and also to the constant current source I4. Now, assuming that the current value of the constant current source I4 is 2I0, the base potential difference of the transistors Q5 and Q6, that is, the potential difference of the external control terminal T1 is VA = VB5.
Assuming −VB6, the collector currents IC5 and IC6 of the transistors Q5 and Q6 are (13) and (1), respectively.
It is expressed as in equation 4).

[0025]

By substituting the equation (12) into the equation (14), the following equation (15) is obtained.

[0027]

On the other hand, the collector current IC of the transistors Q3 and Q4 is input by inputting the voltage of VA to the differential amplifier circuit including the transistors Q3 and Q4 and the constant current source I3.
3, IC4 is expressed by the following equations (16) and (17).

[0029]

However, the current value of the constant current source I3 is I0.

Next, the collectors of the transistors Q4 and Q6 are commonly connected to the load resistance RL, and the load resistance RL is connected.
When the output vo is taken out from both ends of the output vo, the output vo is expressed by the following equation.

[0032]

Therefore, the DC voltage of the output is I0 × RL,
It is a constant voltage regardless of the control voltage VA, and the gain can be varied by the control voltage VA only for the AC component.

Now, consider the output amplitude with VCC = 5V. The base potentials of the transistors Q1 and Q2 are at least 2 of the base-emitter voltage VBE of the transistors when the constant current sources I1 and I2 are transistors.
Since more than twice is necessary, V1 = 2V is set. Considering the base voltage of the transistors Q3 to Q6, that is, the control voltage of the control terminal T1, the constant current sources I3 and I4 are composed of transistors, so it is necessary to lower the power supply voltage by 2VBE or more. Therefore, the voltage of the terminal T1 can be set to 3V, and the output amplitude can be maximized up to 3VPP.

FIG. 2 is a circuit diagram showing a voltage controlled amplifier circuit according to the second embodiment of the present invention.

In FIG. 2, this embodiment is based on np in FIG.
By replacing the n-transistor and pnp-transistor with the reverse pnp-transistor and npn-transistor,
Along with this, other configurations are inevitably changed. The operation of this circuit is similar to that of the first embodiment.

In FIG. 2, the constant voltage source V1 may be connected not between the ground side but between the wiring of the constant voltage source V2 and the input signal source vi.

[0038]

As described above, according to the present invention, the gain is changed by the transistor that constitutes the differential amplifier circuit that amplifies the input signal, and especially by the differential amplifier circuit that is constituted by the reverse junction transistor. In comparison with the conventional voltage control amplifier circuit, the allowable range with the output potential can be widened.
That is, there is an effect that the output amplitude can be increased.

For example, if the power supply voltage is 5V, the potential of the control terminal T1 can be set to a high potential of 3V or more. Therefore, the output vo can be allowed up to 3V. This is 1.5 compared to the conventional voltage controlled amplifier circuit.
The effect is that the amplitude can be doubled.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a voltage controlled amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional voltage control amplifier circuit.

[Explanation of symbols]

 Q1 to Q6 transistors I1 to I4 constant current sources V1 and V2 constant voltage sources vi input signal source vo output T1 control terminal RL load resistance RE emitter resistance

Claims (2)

[Claims] 1. A first and second transistor to which an input signal is applied to a base, a first emitter resistor connecting emitters of the first and second transistors, and the first and second transistors. A first differential amplifier circuit having first and second constant current sources connected to the emitters of the transistors and emitters of the third and fourth transistors are connected to form a third constant current source. By connecting the connected second differential amplifier circuit and the emitters of the fifth and sixth transistors to each other,
And a third differential amplifier circuit connected to the constant current source of the third transistor, the collector of the second transistor is connected to a common connection point of the emitters of the fifth and sixth transistors. The bases of the third and sixth transistors are commonly connected to form a first control terminal, and the bases of the fourth and fifth transistors are commonly connected to form a second control terminal.
Voltage control amplifier circuit, wherein the collectors of the fourth and sixth transistors are connected to a load resistor and an output terminal. 2. The first and second transistors and the third to sixth transistors have opposite polarities to each other.
The voltage control amplifier circuit according to.