JP3283981B2 - Differential amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier using a current mirror circuit as a collector-side load of a differential amplification transistor.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of this type of differential amplifier circuit. That is, a pair of differential input stage transistors Q1, Q2
A circuit in which both emitters are connected to a common constant current source I1, an emitter is a positive power supply Vcc, and resistors R1, R2 are connected between collectors and bases of current input side transistors Q3, Q5.
2, the current output transistors Q4 and Q6 are provided with current mirror circuits 1 and 2 having a current gain multiplying function, and the input sides of the current mirror circuits 1 and 2 are connected as loads on the differential pair Q1 and Q2. Then, the bases of the current input side transistors Q3 and Q5 are commonly connected to form a differential amplifier.

In this differential amplifier, an AC signal is supplied from a transistor Q1, a transistor Q2, a resistor R2, and a resistor R.
1 circulates in the electrically closed circuit formed by the circuit 1 and the common base of the transistors Q3 and Q5 is a virtual ground point (that is, a reference point at which the potential does not move) grounded in an alternating current. , Acting as an alternating load.

Therefore, the voltage amplification factors G1 and G2 are
It is obtained by the equivalent emitter resistance re of the transistors Q1 and Q2 and the resistances R1 and R2, respectively, and is given by G1 = R1 / 2re G2 = R2 / 2re. Therefore, the desired gain is determined by the resistances R1, R
2 may be selected as an AC load, and the AC voltage generated by this resistor is transmitted to the output transistors Q4 and Q6 of the current mirror circuits 1 and 2.

Here, β of the output bias current when there is no signal in the current mirror circuits 1 and 2 of the differential amplifier shown in FIG.
The dependence on (current amplification factor of common emitter) will be considered. That is, the output side transistors Q4 of the current mirror circuits 1 and 2,
The base potential of Q6 is the input transistor Q
3 and Q5 are applied in a form in which the base current Ib and the voltage generated by the resistors R1 and R2 are added to the common base potential (Vbel), so that the output bias (DC) currents I2 and I2
3 is obtained by the following equations.

I2 = IC exp (R1 · Ib / VT) = IC exp (R1 · IC / VT · β) I3 = IC exp (R2 · Ib / VT) = IC exp (R2 · IC / VT · β) ( IC is the bias current of the input transistors Q3 and Q5 of the current mirror circuits 1 and 2 when there is no signal).
2, I3 has β dependence, and depending on its value, I2, I3
Output bias current increases or decreases.

Therefore, if the values of the AC load resistances R1 and R2 are set to be large in order to obtain a high gain in the differential amplifier, the dispersion of the output bias currents I2 and I3 of the current mirror circuit when there is no signal due to β can be reduced. Increase.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and even if the resistance values corresponding to the resistors R1 and R2 are set to be large in order to obtain a high gain, the present invention is not limited thereto. It is an object of the present invention to provide a differential amplifier capable of setting an output bias current at the time of no signal of a current mirror circuit without depending on β.

[0009]

According to the present invention, a differential pair of transistors supplied with a constant current bias from a first power supply electrode is used as an input stage. A pair of current mirror circuits each having a current power multiplication effect on a current output by providing a resistor between a collector and a base of the current input side transistor, using the emitter of the output side transistor as a second power supply electrode; The collectors of the side transistors are connected to the collectors of the transistors of the differential pair, respectively, and the bases of the current input side transistors of the current mirror circuits are commonly connected to form a common base. Prevents the base current of the current input transistor from flowing through the resistor of each current mirror circuit A differential amplifier, characterized in that connecting the bias circuit because.

That is, according to the present invention, in the prior art, the output bias currents I2 and I3 are set to the common base current Ib of the current input side transistors Q3 and Q5 of the current mirror circuit.
, The common base current Ib does not need to flow through the resistors R1 and R2, so that the common base current Ib can be ignored. Being able to configure a differential amplifier that can realize the equivalent function that the output bias current of the current mirror circuit when there is no signal can be set without depending on β It is.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of the embodiment.
Since this is an example in the case of making it correspond to that of FIG. 4, the corresponding portions are denoted by the same reference numerals, and the feature points will be described.

The feature of FIG. 1 is that the current mirror circuits 1, 2
Is connected to a common base of the transistors Q3 and Q5 on the current input side, and a bias circuit 21 for blocking the base current of the transistors Q3 and Q5 on the current input side to the resistors R1 and R2 of each current mirror circuit.

That is, in FIG. 1, in order to extract a base current corresponding to β from the common base of the transistors Q3 and Q5, a PNP in which a bias current is applied from a constant current source I4.
A transistor Q7 is provided, its emitter is connected to the power supply Vcc, a resistor R3 is connected between the collector and base of the transistor Q7, and a resistor R3 is connected from the collector of the transistor Q7.
4 to a common base of the transistors Q3 and Q5.

Here, for example, the resistance values of the resistors R3 and R4 may be set in accordance with the current ratio of the constant current sources I1 and I4.
3 and Q5, the base current Ib of the transistors Q3 and Q5 in FIG.
It is easy to take out a current equivalent to that from the common base of the transistors Q3 and Q5.

As described above, the current sources I1-I4 and the resistance R
By setting the ratio of 3 to R4 in accordance with the base currents of the currency mirror circuits 1 and 2, a base current Ib corresponding to each β can be extracted from the common connection point of the transistors Q3 and Q5. The current Ib is connected to the resistors R1, R2
Therefore, the output bias currents I2 and I3 of the current mirror circuit when there is no signal are set in an equivalent state if they do not depend on β.

FIG. 2 is an improvement of FIG. 1 in which the emitters R5 to R9 are inserted into the transistors of the current mirror circuits 1 and 2 and the bias circuit 21 so that the transistors of the circuits 1, 2 and 21 are early. Effect countermeasure, base-emitter voltage V between transistors requiring pair
This is an example in which the variation in be is improved.

FIG. 3 shows that a differential amplifier in which the polarity of the transistor used is inverted can be configured. Here, the signs of the transistors used are Q101 to Q1.
It is shown as 07. In the circuit example of FIG. 3, a current is supplied from the bias circuit 21 to the common base of the transistors 103 and 105 so that β does not depend on the current (so that no current flows through the resistors R1 and R2). Can be set without depending on β.

[0018]

As described above, according to the present invention, even when an attempt is made to obtain a high gain, the no-signal output bias current of the current mirror circuit serving as a load can be set without depending on β. A dynamic amplifier can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional differential amplifier.

[Explanation of symbols]

1, 2, current mirror circuit, 21 bias circuit, Q
1 to Q7: transistors, R1 to R4: resistors, I1, I
4 ... Current source, Vcc ... Power supply.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 3/45

Claims (2)

(57) [Claims] An input stage uses a differential pair of transistors to which a constant current bias is supplied from a first power supply electrode, and loads the collectors of these transistors with current input and output side emitters as second power supply electrodes. And a pair of current mirror circuits provided with a resistor between the collector and the base of the current input side transistor and having a current gain multiplication effect on the current output, the collector of the current input side transistor being connected to the differential pair. The bases of the current input side transistors of the respective current mirror circuits are connected in common to form a common base. The common base is connected to the resistors of the respective current mirror circuits. Connected a bias circuit to prevent the base current of the input transistor from flowing Differential amplifier characterized by and. 2. The bias circuit according to claim 1, further comprising a transistor to which a constant current bias is supplied from the first power supply electrode, an emitter of the transistor connected to the second power supply electrode, and a first resistor connected between the collector and the base. 2. The differential amplifier according to claim 1, wherein a collector-side end of the resistor is connected to the common base via a second resistor.