JPH0628325B2 - Automatic gain control amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an automatic gain control amplifier of the present invention, and particularly to an automatic gain control amplifier (Auto Gain Control Amplifier) suitable for operation in a low voltage power supply.
Circuit: Hereinafter, A, G. (Abbreviated as C circuit).

[Conventional technology]

The conventional device has an analog integrated circuit (Modern Science Co., Ltd., Shuji Nakazawa, Gen Sasaki, Kiyotaka Murase, 1975), as described on pages 283 to 287, with a single constant current source and two transistors. They were stacked vertically, like steps and load resistance. Therefore, a power supply voltage that is one stage higher than that of a differential amplifier having a pair of transistors (differential amplifier) is required.

This will be described in detail with reference to FIG.

FIG. 3 is a circuit diagram showing an example of a conventional AGC circuit.

In the conventional AGC circuit, the differential pair 151 of the differential amplifier 15 and the transistor pair 161 of the shunt circuit 16 are connected in parallel, and the control circuit 17 includes the differential pair 151 of the differential amplifier 15 and the transistor pair of the shunt circuit 16. 161 and each of them are connected in series.

When the input signal is input between the bases of the differential pair 151, the differential amplifier 15 amplifies and outputs the amplified signal between the collectors of the differential pair 151. Further, the shunt circuit 16 equally draws currents from both the load resistors 9 and 10.

The control circuit 17 forms a differential pair with the transistors 21 and 22, and the constant current source 12 supplies currents Ie ₃ and Ie _{4 to} the differential pair 151 of the differential amplifier 15 and the transistor pair 161 of the shunt circuit 16.
The ratio of the currents Ie ₃ and Ie ₄ is controlled by the differential pair according to the AGC control signal while keeping the sum of the above constant. This allows
The gain of the differential amplifier 15 is controlled.

As described above, in the conventional AGC circuit, the control circuit 17 is directly connected to the differential amplifier 15 and the shunt circuit 16, and a high power supply voltage is required.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, in order to control the current flowing through the pair of differential amplifiers, the differential pairs are further connected in cascade. Therefore, it is necessary to increase the power supply voltage for one stage of the transistor as compared with the case of using only one pair of differential amplifiers. For this reason, as miniaturization of the LSI progresses, the withstand voltage of the element becomes low, so that the power supply voltage cannot be made high, so that there is a problem that a circuit requiring a high power supply voltage cannot be installed or the dynamic range cannot be obtained.

The object of the present invention is to solve the above-mentioned problems of the prior art,
An object of the present invention is to provide an automatic gain control amplifier with a low power supply voltage.

[Means for solving problems]

In order to achieve the above object, in the present invention, an automatic gain control amplifier is composed of a differential pair of a first transistor and a second transistor (hereinafter, simply referred to as a differential pair). The respective collectors of the transistors are connected to the first constant voltage source via the first and second resistors, respectively, and the emitters of the first and second transistors are connected to each other via the first constant current source. It comprises a differential amplifier configured by grounding, and a transistor pair of a third transistor and a fourth transistor (hereinafter, simply referred to as a transistor pair), and collectors of the third and fourth transistors are respectively connected to the first transistor. And connected to each collector of the second transistor,
Further, the emitters of the third and fourth transistors are connected to each other and are grounded via a second constant current source, and the bases of the third and fourth transistors are second to each other.
A shunt circuit configured by biasing with a constant voltage source, and a current is connected to the first constant voltage source and connected to the emitters of the differential pair and the emitters of the transistor pair. Are supplied to the differential pair and the transistor pair while keeping the sum of currents flowing from the first constant voltage source through the first and second resistors constant, respectively, according to a control signal. And a control circuit having a variable current source.

[Action]

The control circuit includes a emitter connected to a differential pair of the differential amplifier and an emitter connected to the transistor pair of the shunt circuit by a current source connected to a power supply which is a first constant voltage source provided in the control circuit. By supplying a current to the point according to the control signal, the sum of the currents flowing from the first constant voltage source through the first and second resistors respectively flows to the differential pair and the transistor pair while maintaining a constant sum. Change the current ratio.

Thus, the control circuit is not connected in series to the differential amplifier or the shunt circuit, and sufficient gain control can be performed, so that the AGC circuit does not require a high power supply voltage.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

The AGC circuit of FIG. 1 includes a differential amplifier 15 and a shunt circuit 16.
And a control circuit 17.

The control circuit 17 controls the differential amplifier 15 according to the AGC control signal.
Shunt circuit 16 that increases or decreases the current Ie ₃ flowing through the differential pair 151 and further partially carries the current flowing through the load resistors 9 and 10.
Control the current Ie ₄ to the transistor pair of.

That is, the currents Ie ₃ and Ie ₄ flowing through the differential pair 151 of the differential amplifier 15 and the transistor pair 161 of the shunt circuit 16 are controlled by keeping the currents Ie ₁ and Ie ₂ of the current sources 5 and 6 constant. By flowing the control currents Ic ₁ and Ic ₂ from the circuit 17 through the constant current sources 5 and 6, the currents Ie ₃ and Ie ₄ flowing through the differential pair 151 of the differential amplifier 15 and the transistor pair 161 of the shunt circuit 16 are increased or decreased. . The relationship of the above currents is shown below.

Ie ₃ = Ie ₁ −Ic ₁ Ie ₄ = Ie ₂ −Ic ₂ Here, Ie ₁ and Ie ₂ are constant. At this time, in order to prevent the DC level of the output signal from changing, the current flowing through the load resistors 9 and 10 It is necessary to change the current ratio of the differential amplifier 15 and the shunt circuit 16 while keeping the sum of the above constant. Therefore, the control circuit 17 controls the load resistances 9, 1
The current of the shunt circuit 16 is controlled so that the sum of the currents flowing to 0 is kept constant. That is, Ic ₁ + Ic ₂ = constant condition. As a result, the current I _RT flowing through the load resistors 9 and 10 becomes constant. This relationship is shown below.

I _RT = Ie ₃ + Ie ₄ = Ie ₁ -Ic ₁ + Ie ₂ -Ic ₂ = Ie ₁ + Ie ₂ -Ic ₁ -C +
A specific example of _{Ic 1 = Ie 1 + Ie 2} -C = control at a constant first view circuit 17 will be described with reference to Figure 2.

This circuit includes PNP transistors 33 to 36, NPN transistors 37 to 40, resistors 41 to 44, constant current sources 31 and 32, a constant voltage source 46, and a voltage source 45.
Connected as shown.

The voltage source 45 is controlled by an AGC control signal, and the transistors 33 and 34, 35 and 36 form a differential pair, and the collectors of the PNP transistors 33 to 36 are connected to the collectors of the NPN transistors 37 to 40, respectively. Connected, transistors 33 and 34, and 35 and 3
The six emitters are commonly connected and are connected to the power supply V _CC through current sources 31 and 32, respectively. Further, the bases of the transistors 33 and 36 are commonly connected to the positive side of the voltage source 45, and the bases of the transistors 34 and 35 are commonly connected to the negative side of the voltage source 45. Then, a current difference ΔIe is generated in the differential pair by the AGC control signal. Further transistors 37-40
Has its emitter grounded through resistors 41 to 44, and transistors 37 and 38 and resistors 41 and 42 form a current mirror circuit so that currents I ₃₇ and I ₃₈ flowing through the emitters of transistors 38 and 37 become the same. Is set to. Similarly, transistors 39 and 38 and resistors 39 and 40 form a current mirror circuit, and currents I ₃₉ and I ₄₀ flowing through the emitters of the transistors 39 and 38 are set to be equal.

Now, assuming that the collector current I ₃₄ of the transistor 34 changes by ΔI ₁ due to the increase of the voltage of the voltage source 45 by the AGC control signal, the collector current I ₃₃ of the transistor ₃₃ and the emitter currents I _{37 of} the transistors 37 and 38, I ₃₈ is
The current of the constant current source 31 as Ie _5, the _{I 33 = Ie 5/2 +} △ I 1 I 37 = I 38 = Ie 5 / 2- △ I 1. As a result, the output current IC ₁ of the control circuit 17 is Ic ₁ = I ₃₃ −I ₃₇ = 2 · ΔI ₁ . Similarly, collector currents I ₃₅ and I ₃₆ of the transistors ₃₅ and ₃₆ and emitter currents I of the transistors 39 and 40
_39, I ₄₀ is a variation of the △ I ₂ of I _36, when the current of the constant current source 32 and _{Ie 6, I 36 = I 40} = I 39 = Ie 6/2 + △ I 2 I 35 = Ie 6 / ₂ −ΔI ₂ , and the output current Ic ₂ of the control circuit 17 becomes Ic ₂ = I ₃₅ −I ₃₉ = 2 · ΔI ₂ . If Ie ₅ = Ie ₆ , the current changes ΔI ₁ and ΔI ₂ due to the voltage change of the voltage source 45 become equal, so Ic ₁ + Ic ₂ = 2 ΔI ₁ -2 ΔI ₂ = 0 In the circuit, the conditions Ic ₁ + Ic ₂ = constant of the output currents Ic ₁ and Ic ₂ of the control circuit 17 are satisfied.

According to this embodiment, the control circuit 17 of the AGC circuit is not connected in series to the differential amplifier 15 and the shunt circuit 16, so that the power supply voltage V _CC can be lowered.

〔The invention's effect〕

According to the present invention, since the power supply voltage of the AGC circuit can be reduced, it is possible to mount the AGC circuit on an LSI having a low withstand voltage.
In addition, it is possible to realize an AGC circuit that performs the same operation as the conventional one even under a low power supply voltage and can obtain a sufficient dynamic range.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a circuit diagram showing a specific example of the control circuit in the figure, and FIG. 3 is a circuit diagram showing a conventional example of the AGC circuit. 1-4, 21, 22, 37-40 ... NPN transistor, 33-36 ... PNP transistor, 5, 6, 1
2, 13, 31, 32 ... constant current source, 7, 8 ... current source, 11, 24, 46 ... constant voltage source, 23, 45 ... voltage source, 9, 10, 37 to 44 ... resistance .

Claims (1)

[Claims] 1. A differential pair of a first transistor and a second transistor (hereinafter, simply referred to as a differential pair).
And each collector of the second transistor is connected to the first constant voltage source via the first and second resistors, respectively, and
A differential amplifier configured by connecting the emitters of the first and second transistors to each other and grounding them via a first constant current source, and a transistor pair of a third transistor and a fourth transistor (hereinafter, simply A pair of transistors), connecting the collectors of the third and fourth transistors to the collectors of the first and second transistors, respectively,
Further, the emitters of the third and fourth transistors are connected to each other and are grounded via a second constant current source, and the bases of the third and fourth transistors are second to each other.
A shunt circuit configured by biasing with a constant voltage source, and a current is connected to the first constant voltage source and connected to the emitters of the differential pair and the emitters of the transistor pair. Are supplied to the differential pair and the transistor pair while keeping the sum of currents flowing from the first constant voltage source through the first and second resistors constant, respectively, according to a control signal. An automatic gain control amplifier, comprising: a control circuit having a variable current source.