JPS6363207A - Operational amplifier - Google Patents

Abstract

PURPOSE:To drive a >= 1000 pF capacity in a wide range without using a PNP with a poor frequency characteristic by using the composite transistor of a channel P MOS and an NPN transistor for an AC signal bus. CONSTITUTION:The composite transistor 5 where the channel P MOS transistor M1 and the NPN transistor Q1 are connected and a composite transistor 6 where the channel P MOS transistor M is connected to the PNP transistor Q2 are used for an initially staged amplifier. Where the propagation conductance of the MOS and the current amplification factor of the NPN transistor are denoted as gmM and hFE, respectively, the propagation conductance GM of the composite transistor is shown by GM = hFE X gmM. Since the current amplification factor hFE is about >= 100, a great propagation conductance can be obtained. As for the unity gain frequency fuM of the MOS, the frequency characteristic of the composite transistor is improved by inserting breeder resistances R1 and R2 between the base and emitter of the NPN, for instance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an operational amplifier using a composite transistor of bipolar and MOS, and more particularly to an operational amplifier using a composite transistor.

[Conventional technology]

As shown in FIG. 4, a conventional bipolar operational amplifier has an input transistor Q21 of a first-stage differential amplifier 101.
．． A type using a lateral PNP as Q22 and a type using a vertical PNP as the sink side transistor Q37 of the push-pull final stage 102 as shown in FIG. 6 are known.

G23.24 is an active load, A22 is a second stage inverting amplifier, Ct is a Miller capacitance, QB9. G40, R31
are the transistors and resistors that make up the bias circuit that makes this operational amplifier class AB; G36 is the second-stage emitter-grounded amplification transistor; 121 and I32 are constant current sources; G38
11, 12, 21, 22 are input terminals, 23.33 is an output terminal, and 24.34 is a positive power supply terminal. G1 is a first stage transconductance amplifier.

[Problem that the invention seeks to solve]

The PNP transistor of the conventional operational amplifier mentioned above has a unity gain frequency of horizontal PNP (several MH2) and vertical PNP
NP has a low frequency of 10 MHz at most, and its phase lag makes it difficult to design a wideband operational amplifier because special circuit techniques such as feedforward must be used, and it also has the disadvantage of oscillation when driving a capacitive load. There is.

In contrast to the conventional operational amplifier described above, the present invention has an original content in that it combines a P-channel MOS transistor and a bipolar NPN transistor and applies its high input impedance, high transconductance, and high frequency characteristics to the input stage and output stage of the operational amplifier. has.

[Means for solving problems]

In the operational amplifier of the present invention, the constant current source, the source of the first P-channel MOS transistor, and the collector of the first NPN transistor are short-circuited.

A first composite transistor in which the drain of the first MOS transistor and the base of the first NPN transistor are short-circuited, and the source of the second P-channel MOS transistor and the collector of the second NPNI-transistor are short-circuited. a second composite transistor in which the drain of the second MOS transistor and the base of the second NPN transistor are short-circuited;
．． The present invention is characterized by comprising a differential amplifier in which the second MOS transistor has a common source.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the invention. A composite transistor 5, in which the source of the P-channel MOS transistor M1 and the collector of the NPN transistor Q1 are connected, and the drain of Ml and the base of Ql, and the P-channel MOS transistor
A composite transistor 6 formed by connecting the source and collector of the OS transistor M1 to the collector and base of the NPN transistor Q2, respectively, is the PN transistor of the first stage amplifier in FIG.
P transistor Q21. 9 used instead of G22 The transfer conductance GM of this composite transistor is M
If the transfer conductance of the OS is expressed as g-M, and the current amplification factor of the NPN transistor is expressed as hre, then G ha = h
teX g m1i1
(1) becomes. Since hre is usually 100 or more, it also has the advantage of realizing a larger transfer conductance than the conventional PNP input type. Also, regarding the frequency characteristics,
The unity gain frequency f, - of the MOS is expressed as ``fu''2z (CGS+CGD'') when the capacitance between the gate and source of the MOS is expressed as COS, and the capacitance between the gate and drain is expressed as COD.In order to make full 10MHz or more, Assuming that the gate capacitance is o, o2p F, gmM should satisfy the following conditions.

g, w>2πx 107xO, 02p=1. Ha μ (3
) The geM of MOS is g-, = 2XKX W L XIo (
4), so K-25μAV-2) W/L=
2, it is sufficient for the ID to flow several μA. Therefore, as shown in Figure 2, the N of the composite transistor is
Bleeder resistors R1, R, 2 between the base and emitter of PN
or by inserting a constant current source I2 as shown in FIG.
．． P channel MOS transistors M1, M2 by I3
All you have to do is apply a bias current to. On the other hand, since the unity gain frequency of an NPN transistor is several hundred MHz, the frequency characteristics of a composite transistor can exceed those of a conventional differential amplifier using PNP.

As mentioned above, since a high transfer conductance can be obtained, the DC gain of the first stage amplifier can also be high, and since it is a MOS input, the input impedance of the operational amplifier can also be increased.

FIG. 5 shows another embodiment of the present invention in which a composite transistor is applied to the push-pull type final stage. Composite transistor M12. Q17 replaces the conventional PNP transistor Q37 in FIG. 6, and the final stage transistor Q1
8. M12. In order to set the bias current of Ql7, a modified composite transistor in which a P-channel MOS transistor M11 with its gate and drain shorted is inserted between the base and collector of an NPN transistor Q19 is connected between the base of Ql8 and the gate of Ml2. .

The idling current of Mll and Ml2 is Ql7°Ql9
Resistors R11 and R12 connected between the base and emitter of
determined by. As mentioned above, the composite transistor M12. The transfer conductance and frequency characteristics of Q17 are greatly improved compared to conventional transistors, so it can drive a capacitance of 10009 F or more. The figure shows the AB class ratio output, but for the B slope output stage, Mll, Ql
The bias circuit for the 9°R11 modified composite transistor can be omitted. Furthermore, since it is an NPN output transistor, it has the advantage of excellent current driving ability.

〔Effect of the invention〕

As explained above, the present invention is applicable to P-channel MOS and NPN
By using a composite transistor in the AC signal path, it is possible to replace a PNP with poor frequency characteristics and provide an operational amplifier that has a wide band and can drive a capacitance of 1000 pF or more.

[Brief explanation of drawings]

1, 2, 3, and 5 are circuit diagrams of embodiments of the present invention, and FIGS. 4 and 6 are circuit diagrams of conventional examples. 1.2...Input terminal, 3...Output terminal, 4...Positive side power supply terminal, 5,6. ...Composite transistor, 11.
. . . Constant current source, Ml, M2 . . . P channel MOS transistor, Ql, Q2. Q3. Q4...NPN transistor. Agent Patent attorney 1 Susumu Uchihara (Maido, \2'L side power supply

Claims (4)

[Claims] (1) The constant current source, the source of the first P-channel MOS transistor, and the collector of the first NPN transistor are short-circuited, and the drain of the first MOS transistor and the base of the first NPN transistor are short-circuited. The source of the first composite transistor and the second P-channel MOS transistor and the collector of the second NPN transistor are shorted, and the second MOS
A differential amplifier including a second composite transistor in which a drain of the transistor and a base of the second NPN transistor are shorted, and a source of the first and second MOS transistors is configured as a common source. Characteristic operational amplifier. (2) An operational amplifier according to claim 1, wherein a resistor is connected between the base and emitter of the first and second NPN transistors. (3) An operational amplifier according to claim 1, characterized in that a constant current source is connected to the drain sides of the first and second MOSs. (4) The collector of the third NPN transistor is connected to the positive power supply, the emitter is connected to the source of the third MOS of the third composite transistor, and the base of the third NPN and the third MOS of the third composite transistor are connected. An operational amplifier having a push-pull type final stage connected to a fourth composite transistor including a fourth P-channel MOS whose gate and drain are shorted between the gates of the operational amplifier.