JP2716560B2 - Semiconductor integrated circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, and more particularly to an improvement in a variable gain amplifier.

[Conventional technology]

FIG. 2 shows an example of a conventional semiconductor integrated circuit. In the figure, 1 is a power supply voltage terminal, 2a and 2b are input terminals, 3a and 3b are output terminals, Q3 to Q14 are transistors, R1 to R7, R9, and R10 are resistors, IB1 and IB2 are bias current sources, VB1 and VB2. Is a bias voltage source.

This circuit amplifies the signal applied to the differential input terminals 2a and 2b at the portion consisting of transistors Q3, Q4, Q5, Q6, Q7 and Q8 and resistors R1, R2, R3 and R4, and the output terminal It has a function to output to 3a and 3b. The feature of this circuit is that by changing the value of the gain setting resistors R9 and R10, the transistor Q
Transistors Q3, Q6 and Q4, which are equal to the emitter voltage of 9 and Q10,
By changing the base voltage of Q5 and changing the current flowing through the resistors R1 and R2, the gain can be selected to an appropriate value.

[Problems to be solved by the invention]

In the prior art, when the voltage applied to the power supply voltage terminal 1 becomes low, the voltage between the collector and the emitter of the transistors Q7 and Q8 cannot be made sufficiently large, and a signal having a large amplitude is inputted to the input terminals 2a and 2b. There was a problem that it became impossible to do.

An object of the present invention is to provide a semiconductor integrated circuit that can realize a variable gain amplifier that can obtain a large input dynamic range even with a low operating power supply voltage. .

[Means for solving the problem]

A semiconductor integrated circuit according to the present invention comprises first and second transistors, connects a base and a collector of the first transistor to a base of the second transistor, and supplies power to the emitters of the first and second transistors. The current mirror circuit connected to the voltage terminal and the collector thereof are connected to the first mirror.
Third and sixth transistors whose bases are connected to each other, a fourth transistor whose emitter is connected to the emitter of the third transistor, and whose emitter is connected to the sixth transistor. A fifth transistor having its base connected to the base of the fourth transistor, and first and second outputs respectively connected to the collectors of the fourth and fifth transistors. A seventh transistor having a terminal connected to the emitter of the third transistor, a base connected to the first input terminal, and a collector connected to the emitter of the fifth transistor; The base is connected to the second input terminal,
An eighth signal for amplifying a signal input to the first and second input terminals together with the third, fourth, fifth, sixth, and seventh transistors and outputting the amplified signal from the first and second output terminals. Transistors, the emitters are connected to different current sources, the eleventh and twelfth transistors whose bases are connected to the same constant voltage source, and the collectors of the eleventh and twelfth transistors,
The current values of the different current sources are connected to the respective emitters, the collectors are connected to each other, the bases are connected to each other, and the constant current source is connected between the constant current source and a grounded resistor. Together with the eleventh and twelfth transistors by means of a resistor that sets
A ninth and a tenth transistor for controlling a base voltage of the fourth, fifth and sixth transistors; a base of the ninth and tenth transistors; and a second transistor of the current mirror circuit. Connected to the collector.

[Action]

In the present invention, when the amplitude of the input signal is large and the gain is small, the third, fourth, fifth, and sixth base potentials are increased, and the voltage between the collector and the emitter of the transistor in the input stage is set to a sufficiently large value. I do.

〔Example〕

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

FIG. 1 is a circuit diagram showing a semiconductor integrated circuit according to one embodiment of the present invention.

In the figure, the same reference numerals as those in FIG.
8, R11 is a resistor, Q1 is a first transistor, and Q2 is a second transistor. A current mirror circuit is formed by the first transistor Q1, the second transistor Q2, the resistors R8 and R11, and the output current of the current mirror circuit, that is, the collector current of the first transistor Q1, is equal to the third transistor Q3. This is proportional to the sum of the collector currents of the sixth transistor Q6.

Now, let us consider a case where the circuit is operated as an amplifier having a small gain and handles an input signal having a large amplitude, that is, a case where the resistor R9 for gain setting is selected to a value larger than R10. In this case, the emitter potential of the transistor Q10,
The base potential of the transistor Q4 and the fifth transistor Q5 becomes lower than the base potential of the third transistor Q3 and the sixth transistor Q6, the collector current of the transistors Q4 and Q5 decreases, and the gain decreases. The collector currents of Q3 and Q6 increase, and the output current of the current mirror circuit increases. Bias current source IB1 and resistor R
7 is for determining the base potential of the transistors Q3, Q4, Q5 and Q6, and flows so that the output current of the current mirror circuit is added to the output current of the current source IB1. The other terminal potential rises and the base potential of the transistors Q3, Q4, Q5 and Q6 rises. As a result, the voltage between the collector and the emitter of the transistors Q7 and Q8 increases, and a signal having a large amplitude can be input.

Also, when operating as an amplifier having a large gain, that is, when the gain setting resistor R10 is selected to be larger than the resistor R9, the collector currents of the transistors Q3 and Q6 decrease, and the terminal of the resistor R7 which is not on the ground side is reduced. Since the potential drops, the base potential of the transistors Q3, Q4, Q5 and Q6 drops,
The collector current of the transistors Q4 and Q5 increases and the resistance R1
Even if the voltage drop at R2 increases, the transistors Q4 and Q5 will not saturate. In addition, although the voltage between the collector and the emitter of the transistors Q7 and Q8 is reduced, it is not necessary to input a large-amplitude signal to the input because the transistors Q7 and Q8 operate as an amplifier having a large gain.

〔The invention's effect〕

As described above, according to the present invention, the first and second transistors are connected, the base and collector of the first transistor are connected to the base of the second transistor, and the emitters of the first and second transistors are connected. A current mirror circuit connected to a power supply voltage terminal, third and sixth transistors whose collectors are connected to the collector of the first transistor, bases are connected to each other, and whose emitter is the third transistor Fourth connected to the emitter of the transistor
And a fifth transistor whose emitter is connected to the emitter of the sixth transistor, and whose base is connected to the base of the fourth transistor; and the collectors of the fourth and fifth transistors, respectively. A connected first and second output terminal, a collector of which is connected to an emitter of the third transistor, a base of which is connected to a first input terminal of a seventh transistor, and a collector of which is connected to the third transistor. 5, the base of which is connected to the second input terminal,
An eighth signal for amplifying a signal input to the first and second input terminals together with the third, fourth, fifth, sixth, and seventh transistors and outputting the amplified signal from the first and second output terminals. Transistors, the emitters are connected to different current sources, the eleventh and twelfth transistors whose bases are connected to the same constant voltage source, and the collectors of the eleventh and twelfth transistors,
The current values of the different current sources are connected to the respective emitters, the collectors are connected to each other, the bases are connected to each other, and the constant current source is connected between the constant current source and a grounded resistor. Together with the eleventh and twelfth transistors by means of a resistor that sets
A ninth and a tenth transistor for controlling a base voltage of the fourth, fifth and sixth transistors; a base of the ninth and tenth transistors; and a second transistor of the current mirror circuit. When operating as an amplifier with a large input signal amplitude and a small gain, the third, fourth, fifth and sixth base potentials are raised to increase the potential between the collector and the emitter of the transistor in the input stage. The voltage can be made sufficiently high, and there is an effect that a variable gain amplifier that can obtain a large input dynamic range even with a low operating power supply voltage can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a semiconductor integrated circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional semiconductor integrated circuit. 1 is a power supply voltage terminal, 2a and 2b are input terminals, 3a and 3b are output terminals, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12, Q13 and
Q14 is a transistor, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10
And R11 are resistors, IB1 and IB2 are bias current sources, VB1, VB2,
And VB3 are bias voltage sources. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] A first transistor including a first transistor and a second transistor;
A current mirror circuit in which the base and collector of the second transistor are connected to the base of the second transistor, and the emitters of the first and second transistors are connected to the power supply voltage terminal; Third and sixth transistors having their bases connected to each other, connected to the collector, a fourth transistor having its emitter connected to the emitter of the third transistor, and having its emitter connected to the sixth transistor. A fifth transistor connected to the emitter, the base of which is connected to the base of the fourth transistor, first and second output terminals respectively connected to the collectors of the fourth and fifth transistors, A seventh transistor whose collector is connected to the emitter of the third transistor and whose base is connected to the first input terminal.
And a collector thereof is connected to the emitter of the fifth transistor, a base thereof is connected to the second input terminal, and the third transistor, the fourth, the fifth, the sixth, and the seventh transistor together with the third transistor. 1
And the signal input to the second input terminal is amplified to
An eighth transistor that outputs from the second output terminal; eleventh and twelfth transistors whose emitters are connected to different current sources and whose bases are connected to the same constant voltage source; The collector of the twelve transistors and their respective emitters are connected, the collectors are connected to each other, the bases are connected to each other, and the constant current source and one end thereof are connected to a grounded resistor. Together with the eleventh and twelfth transistors by means of resistors for setting the current values of different current sources, the third, fourth, fifth,
Ninth and tenth transistors for suppressing the base voltage of the sixth transistor, wherein the bases of the ninth and tenth transistors are connected to the collector of the second transistor of the current mirror circuit. Characteristic semiconductor integrated circuit.