JPH066607Y2 - Gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a gain control circuit suitable for an electronic volume integrated into a semiconductor integrated circuit and capable of operating at a low voltage.

[Prior art]

The conventional gain control circuit is composed of two differential amplifier circuits as shown in FIG. 3, and includes a transistor differential pair including transistors 21 and 22 and a current source transistor 23.
And a differential amplifier circuit A ₁₀ and transistors 24, 2
The differential amplifier circuit A _{20 includes} a transistor differential pair of 5 and a current source circuit 26, and a variable voltage source 27 for gain control applied between the bases of the differential pair transistors. A signal source 28 superimposed on a bias voltage source 29 is connected to the base of the current source transistor 23, and the voltage between the bases of the transistor differential pair is controlled by adjusting the voltage of the variable voltage source 27. Adjusting the gain.

[Problems to be solved by the device]

In the conventional gain control circuit, as shown in FIG. 3, the signal source 28 is superimposed on the bias voltage source 29 and is supplied to the base of the current source transistor 23 of the differential amplifier circuit. Therefore, it is necessary to temporarily reduce the DC level and amplitude of the signal by using a normal level shift circuit and supply the signal to the base of the current source transistor 23 of the differential amplifier A ₁₀ . The output is obtained as the voltage across the terminals of the load resistance.
Therefore, as shown in FIG. 3, the conventional gain control circuit needs to make the power supply voltage Vcc relatively high, and there is a problem in operation at a low voltage of about 1V. Furthermore, since a signal is input via the current source transistor 23, there is a drawback that diode distortion is superimposed on the signal.

The present invention has been made to solve these problems, and its main purpose is to provide a gain control circuit suitable for low voltage with a small number of elements.

Another object of the present invention is to provide a gain control circuit in which diode distortion is not superimposed on an output signal.

[Means for solving the problem]

The gain control circuit of the present invention is made in order to solve the above problems, and the present invention is composed of two differential amplifier circuits, one of which is a base transistor of one transistor. Connection point (anode) where collectors are commonly connected
Signal current is supplied to the load, the signal current is supplied to the load as direct current, and these differential amplifier circuits are self-biased. The gain is adjusted by adjusting the current value.

[Action]

One transistor of the two differential amplifier circuits has a self-bias circuit with the base and collector of one transistor of the transistor differential pair connected in common, and a signal current is directly supplied to this common connection point to cause diode distortion in the output signal. Can be prevented, and the gain control defined by the current ratio can be performed by controlling the current source circuits of these differential amplifier circuits. Therefore, it is not necessary to supply a signal via the level shift circuit, the number of elements can be reduced, and operation at low voltage is possible.

〔Example〕

The gain control circuit of the present invention will be described based on the embodiment of FIG.

In FIG. 1, an active load circuit 2 composed of a mirror pair.
0 and a differential pair consisting of transistors 1 and 2 and a differential amplifier circuit A ₁ consisting of a current source circuit 5 connected to a commonly connected emitter thereof, and an active load circuit 2 formed of a mirror pair.
1 is connected to a common connection point of the bases of the transistors ₂ and 6 and a differential amplifier circuit A _{2 including} a current source circuit 10 connected to a commonly connected emitter of the differential pair 1 and transistors 6 and 7. The transistor 1 of the differential amplifier A ₁ is constituted by a bias voltage source 11 and its base and collector are connected to each other to form a self-bias circuit. The signal current i ₁ is supplied to the base / collector of the transistor 1 and the base of the transistor 7, and the gain is adjusted by controlling the current values I ₁ and I ₂ of at least one of the current source circuits 5 and 10.

Next, the operation of the gain control circuit of the present invention will be described with reference to FIG.

First, the differential amplifier circuit A ₁ will be described. The input current is i ₁ and the collector currents of the transistors ₁ and 2 are i
₃ and i _4, and the mirror current from the transistor 4 is i ₅
And Collector currents i ₃ and i _{4 of the} transistors 1 and 2
And the current I ₁ flowing through the current source circuit 5 is expressed by the following relational expression.

I ₁ = i ₃ + i ₄ (1) The signal current i ₁ is supplied to the base / collector of the transistor 1 and the base of the transistor 7. Further, since the base current flowing through the transistors 1 and 7 is so small that it can be ignored, the collector current i ₃ is expressed as follows.

i ₃ = i ₁ + i ₅ (2) The current I ₁ is expressed by the following equation by substituting the equation (2) into the equation (1).

I ₁ = (i ₁ + i ₅ ) + i _{4 Further} , since the mirror currents i ₄ and i ₅ are equal to each other, assuming that the current is i ₀ , the equation (1) is expressed as follows.

I ₁ = i ₁ + 2i ₀ Therefore, the collector current i ₃ is expressed as follows from the equations (2) and (3).

On the other hand, in the differential amplifier circuit A ₂ , if the current of i ₂ flows from the output terminal OUT as the output current, i ₆ and i ₇ flow as the collector currents of the transistors 6 and 7. The collector currents i ₆ and i ₇ and the current I ₂ are represented by the following relational expressions.

I ₂ = i ₆ + i ₇ (5) Also, the mirror current i ₈ from the transistor 9 and the output current i
₂ is represented by the following relational expression with the output current i ₂ .

i ₇ = i ₂ + i ₈ (6) Since the currents i ₆ and i ₈ are equal to each other, assuming that the current is i ₀ , the equation (6) is expressed as follows.

I ₂ = i ₆ + (i ₈ + i ₂ ) I ₂ = i ₂ + 2i ₀ Therefore, the current i ₇ is expressed as follows.

Next, the relationship between the input / output currents i ₁ and i ₂ and the currents I ₁ and I ₂ flowing in the current source circuits 5 and 10 will be described. The base-emitter voltage V _BE1 of the transistor ₁ and the base-emitter voltage V _BE2 of the transistor 2 are expressed as follows.

[However, V _T is a thermal voltage and I ₀ is a reverse saturation current] Therefore, when the difference voltage between the input voltage and the reference voltage 11 is ΔV _BE , it is expressed as follows.

ΔV _BE = V _BE1 −V _BE2 = V _T 1n [(I ₁ + i ₁ ) / (I ₁ −i ₁ )] ……………………
(11) Further, the differential amplifier circuit A ₂ will be described. Base-emitter voltage V _{BE3 of} transistor 6 and transistor 7
The base-emitter voltage V _{BE4 of} is expressed as follows.

Therefore, when the difference voltage between the input voltage and the reference voltage 11 is ΔV _BE , the following relationships are established.

ΔV _BE = V _BE3 −V _BE4 = V _T 1n [(I ₂ + i ₂ ) / (I ₂ −i ₂ )] ……………………
(14) Therefore, the input / output currents i ₁ and i ₂ and the currents I ₁ and I ₂ are represented by the following relationships from the expressions (11) and (14).

Therefore, the relationship between the input currents i ₁ and i ₂ and the currents I ₁ and I ₂ is expressed by the following equation.

That is, the gain control circuit of FIG. ₁ can control the gain by changing the ratio of the currents I ₁ and I ₂ .
Further, as is clear from the equation (15), the component of the output current i ₂ does not include the factor due to the diode distortion.

The gain control circuit of FIG. 2 is an embodiment for obtaining an inverted output with respect to an input signal, and the differential amplifier circuit A ₁ has the same connection as that of the embodiment of FIG. The connection of the circuit A ₂ is different. The differential amplifier circuit A ₂ includes a transistor differential pair including transistors 6 and 7, an active load circuit 21 including a transistor 8 and a diode-connected transistor 9, and a current source circuit 10. An output current inverted with respect to the input current i ₁ without using an inverting circuit is derived from the commonly connected collectors of the transistors 6 and 8.

The gain control is performed by the current source circuit 5 on the side of the differential amplifier circuit A _{1. The} current source circuit 5 is configured by a current mirror circuit including a transistor 14 and a diode-connected transistor 15, which is a diode-connected transistor. The gain is controlled by supplying the current I ₁ to 15.

A constant current is passed through the other current source circuit 10.
An output signal current inverted with respect to the input signal is obtained from the output terminal OUT.

[Effect of device]

The gain control circuit of the present invention requires a very small number of elements, and can be operated even with a low voltage source having a power supply voltage Vcc of about 1 V. Moreover, the dynamic range of the output signal is the current source. Currents I ₁ and I flowing in the circuits 5 and 10
It is possible to take up to the limit of ₂ , which is extremely effective.

Further, the output signal i ₂ is supplied from the collector of the differential pair transistor, the diode distortion component is not included in the output unlike the conventional gain control circuit shown in FIG. According to the above gain control circuit, an inverted output can be easily obtained, and an effective gain control circuit can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a variable gain control circuit according to the present invention, and FIG. 2 is a circuit diagram showing another embodiment of a variable gain control circuit according to the present invention. FIG. 3 is a circuit diagram showing a conventional gain control circuit. A ₁ , A ₂ : Differential amplifier circuit IN: Input terminal OUT: Output terminal 1 to 4, 6 to 9: Transistor 5, 10: Current source circuit 11: Bias voltage source 20, 21: Active load circuit

Claims (1)

[Scope of utility model registration request] 1. A first differential amplifier circuit comprising a differential pair comprising first and second transistors having a first active load circuit and a first current source circuit, and a second active load. A second differential amplifier circuit including a differential pair including a third and fourth transistor and a second current source circuit including a circuit, and a base connected to the second and third transistors. An input signal is supplied to a connection point of a bias voltage source, the base / collector of the first transistor and the base of the fourth transistor being connected, and the input signal of the first and second current source circuits is supplied. A gain control circuit, wherein an output is obtained from the second differential amplifier circuit by controlling at least one current value to vary a gain.