JPS6324707A - Current mirror type amplifier circuit with gain control means - Google Patents

Abstract

PURPOSE:To prevent a gain from fluctuating by preventing the fluctuation of a bias voltage, by negating a signal component by inputting a signal whose phase is inverted from that of an input signal, to a current source circuit. CONSTITUTION:From an input terminal 1, an input signal current is inputted, and from an input terminal 2, the input signal current whose phase is inverted, and synchronized, is inputted. meanwhile, to diodeconnected transistors Q2 and Q9, a mirror current limited by a resistance R1, is supplied respectively through a current mirror circuit 11, and current mirror circuits 10 and 12. The input signals supplied from the input terminals 1 and 2, are overlapped on the above mirror currents, and are supplied as forward bias currents of the transistors Q2 and Q9. In this way, when a gain control current from a variable current source circuit 6 is supplied to a point P, the voltage between the terminals fluctuates, and the gain of a current mirror circuit 8 is set, and the signal component is offset, thereby, it is possible to prevent the bias voltage from fluctuating.

Description

[Detailed Description of the Invention] [Industrial Application Field of the Invention] The present invention is an amplifier circuit using a conventional current mirror circuit, and is a current mirror type amplifier circuit equipped with gain control means suitable for semiconductor integrated circuits. It is related to.

[Technical background of the invention]

FIG. 2 shows a current mirror circuit consisting of a diode-connected transistor Q20 and a transistor Q21, an input signal source 22, and a variable resistor R. 3 is an output terminal, 21
is a power supply terminal, and 2o is a variable current source. By supplying the variable current I from the variable current source 2o to the resistor R connected to the emitter side of the transistor Q20, the voltage V between the terminals of the resistor R is varied, and the base voltage of the transistor Q21 is varied, thereby increasing the current. The gain of the mirror circuit changes to vary the output current (2).

As shown in Fig. 2, the signal current and output current are It,
If Iz, I+=I3 ・A, ......(1)1,
=r, ・A2 ......(2) is expressed.

However, A I and A 2 are A + = e ・Vsi
+/VT.

There is a relationship of Az = e-Vstz / VT, and “I
IEl + VIIE2 are each transferred! , evening Q20.
Q21 (7) is the base-emitter voltage. Note that VT is a thermal voltage expressed as kT/q (k is Boltzmann's constant, q is electron charge, and T is absolute temperature), and 2 is a reverse saturation current.

Also, diode-connected transistor Q20゜Q21
Let the base and emitter voltages of VBE I + V be respectively
8 E2 and the voltage between the terminals of the resistor R is expressed as follows.

■1□=VB! +10■ ......(3) Also, the relationship between the signal current 11 and the output current ■2 is (11(2) (3
From equation 1, it is expressed as follows.

Iz"It ・A ......(4) However, A
is A=e·Vgz/Vt. Note that the transistor Q20. The base-emitter voltages of Q21 are considered to be approximately equal when formed on the same semiconductor substrate, and are expressed as {circle around (2)}.

Therefore, the output current I2 is set to be A times the input current 11. That is, by varying the voltage (2) between the terminals of the resistor R, the voltage (2) between the terminals is adjusted and set to a predetermined gain.

However, the current mirror type amplifier circuit shown in FIG. There was room for improvement because the circuit gain fluctuated and the output was distorted.

Furthermore, it is difficult to stably operate a current amplifying circuit equipped with a gain control means with a low voltage source of 1 V or less to obtain a predetermined amplification factor.

[Purpose of the invention]

The present invention was made to solve the above-mentioned problems, and its purpose is to provide a current mirror type amplifier circuit whose gain can be easily controlled.

Another object of the present invention is to provide a current mirror type amplifier circuit with gain control means that operates at low voltage.

[Summary of the invention]

A current mirror type amplifier circuit equipped with gain control means of the present invention includes a current mirror circuit 8 consisting of a transistor Q1 and a diode-connected transistor Q2;
transistor Q3 for the current source. Q4, a resistor R1 connected to the emitter of the transistor Q2, a variable current source circuit 6 for gain control connected to the connection point between the emitter of the transistor Q2 and the resistor R1, and a connection between the transistor Q2 and the transistor Q4. The current source circuit includes an input terminal 1 to which an input signal is input, a connection point between transistors Ql and Q3 is connected to an output terminal 3, and a current source circuit is connected to a resistor R1, and an input terminal 2 is provided to the current source circuit. By inputting to input terminal 2 an input signal whose phase is inverted from that of the input signal supplied from input terminal 1 and canceling the signal component, fluctuations in the bias voltage and gain are prevented. This is what I did.

[Embodiments of the invention]

The current mirror type amplifier circuit of the present invention will be explained based on the embodiment shown in FIG.

In FIG. 1, reference numerals 1 and 2 are input terminals to which input signals whose phases are inverted to each other are applied, 3 is an output terminal, 4 is a power supply terminal, and 5 is a ground terminal. 6 is a variable current source circuit for controlling the gain 41H, 7 is a constant current source circuit, and 8 to 12 are current mirror circuits. The current mirror circuit 8 is formed of a transistor Q1 and a diode-connected transistor Q2, and the current source transistors Q3 . Q4 is
Diode connected transistor Q5. Together with Q6, they form current mirror circuits 9 and 10, respectively. Transistor Q5. The collector and base of Q6 are transistors Q12.
Connected to the collector of Qll. transistor Qll,
Q12 forms a current mirror circuit 11 together with transistor QIO and diode-connected transistor Q13. Transistor Q7. Q8 forms a current mirror circuit 12, and the collector of transistor Q7 is connected to the collector of diode-connected transistor Q9, forming a current source circuit so that mirror current I flows through resistor R1. Transistors Q7 and Q9 are current source circuits in which input signal current from input terminal 2 is superimposed. Further, the base and collector of the diode-connected transistor Q8 are connected to the collector of the transistor Q10. The emitters of transistors Q2 and Q9 to Qll are commonly connected to resistor R1.

In such a current mirror type amplifier circuit, a human input signal current (±ItN) is input from input terminal 1, and the phase is inverted from that of the input signal current (T 1.4') from input terminal 2.
In addition, a synchronized human power signal current (+''■, 9) is input. On the other hand, diode-connected transistors Q2 and Q9
A mirror current (1) limited by a resistor R1 is supplied to the current mirror circuit 11 and the current mirror circuit 10.12, respectively. The input signals supplied from input terminals 1 and 2 are superimposed on their mirror currents 11, so that N, ±
I+J.

A current of (II:j:IIs) is supplied as a forward current to diode-connected transistors Q2 and Q9.

Therefore, transistor Q2. Q9 to Q11 and resistor R1
At the connection point P, the input signal components (±11N), (child ■, 8) whose phases are inverted to each other cancel each other out, and the DC components I,
only flows through resistor R1.

Therefore, when a gain control current of lv is supplied from the variable current source circuit 6 to the point P, the resistor R1 has a voltage of N.

+Iv) current flows. Therefore, an inter-terminal voltage (II +)v)R1 is generated between the terminals of the resistor R1. This inter-terminal voltage (TI+IV) R1 becomes the bias voltage of the transistor Q1, and the inter-terminal voltage of the resistor R1 changes in response to fluctuations in the variable current 1V, thereby setting the gain of the current mirror circuit 8. Also, the voltage between the terminals of resistor R1 (
Since the signal components of the bias voltage of the transistor Q1 are canceled out, the bias voltage does not fluctuate due to this, and if the control current Iv from the variable current tA6 is constant, the gain of the current mirror circuit 8 is constant. be.

Of course, the system? By varying the IU current 9, the gain of the current mirror circuit can be controlled without distorting the output signal.

Note that the output current of the current mirror type amplifier circuit according to the present invention is
. As explained in the conventional example in Fig. 2, Ua is ±T, .
-Represented by A.

In addition, in the current mirror type amplifier circuit of the present invention, the saturation voltage VCE (latl) of the transistor and
Since it is constituted by the voltage (2) between the terminals of the resistor R1 and the terminals of the resistor R1, it operates satisfactorily at approximately 0.9V, and is effective as a low voltage source.

〔Effect of the invention〕

The current mirror type amplifier circuit equipped with the gain control means of the present invention can be used with a low voltage power supply Vcc of 1 or less, and the gain of such a circuit does not vary depending on the amplitude of the input signal. This is a current mirror type amplifier circuit equipped with an excellent gain control means that does not cause distortion in the output, and is extremely effective as an audio amplifier circuit.

Further, the current mirror type amplifier circuit equipped with the gain control means of the present invention is suitable for semiconductor integrated circuits such as gain control circuits, low voltage electronic volume regulators, and attenuators.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a current mirror type amplifier circuit equipped with gain control means according to the present invention, and FIG. 2 shows an amplifier circuit using a conventional current mirror circuit. 1.2; input terminal, 3: output terminal, 4: power supply terminal 5: ground terminal, 6: variable current source circuit, 7: constant current source, 8 to 1
2: Current mirror circuit, Ql to Q13: Transistor,
R1: resistance

Claims (2)

[Claims] (1) The second transistor is diode-connected to the first transistor.
a first current mirror circuit consisting of a transistor, third and fourth transistors for current sources of the first current mirror circuit, a resistor connected to the emitter of the second transistor, and a resistor connected to the emitter of the second transistor; a variable current source circuit for gain control connected to a connection point between the emitter of the transistor and the resistor;
a first input terminal connected to a connection point between the second transistor and the fourth transistor; an output terminal connected to a connection point between the first and third transistors; a current source circuit connected to the current source circuit; and a second input terminal connected to the current source circuit; A current mirror type amplifier circuit equipped with a gain control means that is supplied from a terminal. (2) Each of the current source transistors of the first current mirror circuit is an output stage transistor of the second and third current mirror circuits, and the bias side transistor of the current mirror circuit is a fourth transistor. The emitters of the transistors on the bias side of the first current mirror circuit and the emitters of the transistors on the output stage of the fourth current mirror circuit are connected in common to the transistors in the output stage of the fourth current mirror circuit. A current mirror type amplifier circuit comprising a gain control means according to claim 1 connected to a resistor.