JPS62298209A - Automatic gain control amplifier - Google Patents

Abstract

PURPOSE:To attain the low power voltage by supplying a current to a connecting point of emitters of a differential pair and a connecting point of emitters of a transistor pair and varying the current ratio flowing thereto respectively according to a control signal. CONSTITUTION:Currents Ie3, Ie4 flowing to the differential pair 151 of a differential amplifier 15 and a transistor pair 161 of a current shunt circuit 16 are controlled by making currents Ie1, Ie2 of current sources 5, 6 constant and giving control currents Ic1, Ic2 from a control circuit 17 to constant current sources 5, 6 so as to increase/decrease the currents Ie3, Ie4 flowing to the differential pair 151 of the differential amplifier 15 and to the TR pair 161 of the circuit 16. It is required to change the current ratio of a current of the differential amplifier 15 to that of the circuit 16 in this case while keeping the current sum flowing to load resistors 9, 10 in order to prevent a DC level of an output signal from being changed. Thus, the control circuit 17 controls the current of the circuit 16 to keep the sum of the currents flowing to the load resistors 9, 10 constant.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an automatic gain control amplifier, and in particular to an automatic gain control amplifier (AuωGa1n) suitable for operation with a low voltage power supply.
This relates to the Control 1 circuit (hereinafter abbreviated as A, G, and C circuits).

[Prior Art] The conventional device is as described in Analog Integrated Circuits (Kinda Kagakusha, translated by Shuji Nakazawa, Hajime Sasaki, and Kiyotaka Murase, 1975), pages 283 to 287.

One stage of constant current sources, two stages of transistors, and a load resistor were stacked vertically.

For this reason, a differential amplifier with a pair of transistors (differential amplifier)
This required a power supply voltage that was one stage higher than that of the transistor.

This will be explained in detail using 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 connects the differential pair 151 of the differential amplifier 15 and the transistor pair of the shunt circuit 16 in parallel. 161 and are connected in series.

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

The control circuit 17 includes transistors 21 and 22 that form a differential pair, and a constant current source 12 that controls current 1e flowing through the differential pair 151 of the differential amplifier 15 and the transistor pair 161 of the shunt circuit 16.
The current 1 es in the differential pair according to the AGC control signal while keeping the sum of s and IO2 constant.

Control the ratio of E4. This controls the gain of the differential amplifier 15.

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.

[Problem that the invention seeks to solve]

In the above-mentioned prior art, one more stage of differential pairs is connected in cascade to control the current flowing through the pair of differential amplifiers. Therefore, it is necessary to increase the power supply voltage by one stage of transistors compared to the case where only one pair of differential amplifiers are used. For this reason, as LSI miniaturization progresses, the withstand voltage of the elements decreases, making it impossible to obtain a high power supply voltage), making it impossible to incorporate circuitry that requires a high power supply voltage, and causing problems such as not being able to maintain a dynamic range. Ta.

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide an automatic gain control amplifier that achieves low power supply voltage.

[Means for solving problems]

In order to achieve the above object, the present invention provides an automatic gain control amplifier that includes a differential pair of a first transistor and a second transistor (hereinafter simply referred to as a differential pair). Each collector of the transistor is connected to a first constant voltage source through a first and second resistor, and the emitters of the first and second transistors are connected to each other to connect a first constant current source. A differential amplifier constructed by grounding through the
It consists of a transistor pair of a third transistor and a fourth transistor (hereinafter simply referred to as a transistor pair), and the collectors of the third and fourth transistors are connected 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 grounded via a second constant current source, and the bases of the third and fourth transistors are connected to each other by a second constant current source.
a shunt circuit configured from a constant voltage source K, connected to the first constant voltage source, and connected to a connection point between the emitters of the differential pair and a connection point between the emitters of the transistor pair; and controlling the ratio of currents flowing through each of the differential pair and the transistor pair while keeping the sum of the currents flowing from the first constant voltage source through the first and second resistors constant. The control circuit includes a current source that can be varied according to a signal.

[Function] The control circuit uses a current source connected to a power source, which is a first constant voltage source, provided in the control circuit to connect the emitter connection point of the differential pair of the differential amplifier to the minute point. By supplying current to the emitter connection point of the pair of transistors according to the control signal, the difference between the currents is maintained constant while the sum of the currents flowing from the first constant voltage source through the first and second resistors is kept constant. The ratio of current flowing through the dynamic pair and the transistor pair is varied.

In this way, this control circuit is not connected in series with a differential amplifier or a shunt circuit and can perform sufficient gain control, so the AGC circuit does not require a high power supply voltage.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. 1. The AGC circuit shown in FIG.
and a control circuit 17.

The control circuit 17 controls the differential amplifier 15 according to the AGC control signal.
It increases or decreases the current e3 flowing through the differential pair 151, and further controls the current ea flowing to the transistor pair of the shunt circuit 16 that partially shares the current flowing through the load resistors 9 and 10.

That is, the currents Ie3 and IC4 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 tiIθ1 and Iez of the current sources 5 and 6 constant, and by controlling from the control circuit 17. By flowing the current ICI+IC2 to the constant current sources 5 and 6, the differential pair 15 of the differential amplifier 15
1 and the currents xes and b14 flowing through the transistor pair 161 of the shunt circuit 16 are increased or decreased. The relationship between the above currents is shown below.

Ies = I8N - Ic.

IC4=Iez-IC2 Here, I62 is constant At this time, in order to prevent the DC level of the output signal from changing, the differential amplifier 15 is It is necessary to change the current ratio of the shunt circuit 16 and the current ratio of the shunt circuit 16. Therefore, the control circuit 17 has a load resistance 9
．． The shunt circuit 1
6 current is controlled. That is, IC+ + IC2=C=has a certain condition. As a result, the current tut flowing through the load resistor 9.10 becomes constant. This relationship is shown below.

IR? = IC3+ IC4 =Ie+-Ic+ + IC2-IC2" Ie++I
ez-1c+ -C+ ICI= Ie+ + I82
- C=constant A specific example of the control circuit 17 in FIG. 1 will be explained with reference to FIG.

This circuit consists of PNP transistors 33-36, NPNI
- Ranjistaro 7 to 40, resistor 41 to 44, constant current source 6
1 and 62, a constant voltage source 46, and a voltage source 45,
The connections are made as shown in FIG.

Voltage source 45 is controlled by an ACC control signal), and transistors 66 and 54, 55 and 56 each constitute a differential pair, and the collector of each PNP transistor 56-56 is connected to the NPN transistor 37-40, respectively. transistors 63 and 34 as well as 35 and 6
The emitters of 6 are commonly connected to the power supply ■ through current sources 31 and 32, respectively. Connected to 0. Further, the bases of transistors 66 and 36 are connected in common to voltage source 45.
On the positive side of, and transis,! The paces 234 and 35 are connected in common and connected to the negative side of the voltage source 45, respectively. Then, a current difference l\Ie is generated in the differential pair (by the AGC control signal). Furthermore, the emitters of transistors 37 to 40 are grounded via resistors 41 to 44, and transistors 37.38 and resistors 41.42 form a current mirror circuit, so that currents L57 and Isa flowing through the emitters of transistors 38 and 37 are the same. is set to be. Similarly, transistor 39.38 and resistor 39
．． 40 constitutes a current mirror circuit, and the transistor 39
The t currents I39 flowing to the emitters of and 38 are set so that they are equal to 40.

Now, as the voltage of the voltage source 45 increases due to the AGC control signal, the collector current IS4 of the transistor 64 increases by △1.
If the collector current I of the transistor 53 changes
33 and emitter current l37 of transistor 37.38
1148 is Iss ``Ies/2 + Δ1゜Isy ''L, where the current of the current source 31 is es.
m = Ies/2-Δ1°. As a result, 1 based on the output of the control l path 17 is Ic+ = I33- h7
= 2 ・ΔI.

oSimilarly, if the current of the transistor 55.56 is 55* "54 and the emitter current of the transistor 39.40 is 11?l I4°, the change in Isa is 8I2, and the current of the constant current source 32 is IC4. I3A″work ao = I39 = Iθ6/2 +Δl
2bs=Iea/z-Δ12, and the output current IC2 of the control circuit 17 is Ic2=
bs-I3. = −2・ΔI2. Here I6
s ” If IC6, the current change due to the voltage change of the voltage source 45 ∆ 1 and 12 will be equal, so Ic+ + IC2 = 28 1.-2 to l2 = 0 In the circuit of Fig. 1, the output of the control circuit 17 Current Ic+ and IC2
Satisfies the condition Ic+ + IC2 = constant.

According to this embodiment, since the control circuit 17 of the AGC circuit is not connected in series with the differential amplifier 15 and the shunt circuit 16, the source voltage v0 can be lowered. According to the invention, since the low voltage of the AGC circuit can be made into a source voltage, it is possible to implement it even in LSI with low breakdown voltage.
Furthermore, it is possible to realize an AGC circuit that operates in the same manner as the conventional one even under a low power supply voltage and can obtain a sufficient dynamic range.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing a specific example of the control circuit shown in the figure, and FIG. 3 is a circuit diagram showing a conventional example of an AGC circuit. 1 to 4, 21, 22. 37 to 40...NPN transistor, 33 to 36...PNP transistor, 5,
6゜12.13.31.52... Constant current source, 7.8.
...Current source, It, 24.46... Constant voltage source, 23.
45...Voltage source, 9.10.37-44...Resistance.

Claims (1)

[Claims] 1. Consisting of a differential pair of a first transistor and a second transistor (hereinafter simply referred to as a differential pair);
The collectors of the transistors are connected to a first constant voltage source via first and second resistors, and the emitters of the first and second transistors are connected to each other to connect a first constant current source. It consists of a differential amplifier constructed by grounding through connected to each collector of the first and second transistors;
Further, the emitters of the third and fourth transistors are connected to each other and grounded via a second constant current source, and the bases of the third and fourth transistors are connected to each other by a second constant current source.
a shunt circuit configured by being biased by a constant voltage source; and controlling the ratio of currents flowing through the differential pair and the transistor pair in accordance with a control signal while keeping the sum of the currents flowing from the first constant voltage source through the first and second resistors constant. An automatic gain control amplifier comprising: a control circuit having a variable current source;