JPH0380706A - Operational amplifier - Google Patents

Abstract

PURPOSE:To obtain a stable phase compensation characteristic which is not influenced by a load on an output side and an input/output frequency, etc., by connecting a phase compensating circuit to which a prescribed source follower circuit and a capacity are connected in series, between an input and an output of a gain circuit. CONSTITUTION:The operational amplifier is constituted by providing a differential amplifying circuit 1, a gain circuit 2, an output circuit 3, a source follower circuit 7 containing an NMOS transistor 5 and a resistance 6, and a phase compensating circuit 8 containing a capacity 4 and the source follower circuit 7. Since the source follower circuit exists in the phase compensating circuit for forming a feedback circuit, a stable phase compensation characteristic which is not influenced by a load on an output side and an input/output frequency, etc., is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an operational amplifier, and more particularly to an operational amplifier equipped with a phase compensation circuit suitable for an MO3 type semiconductor integrated circuit.

[Conventional technology]

A conventional operational amplifier, as shown in FIG.
an output circuit 18 connected to the output side of the differential amplifier circuit 17; a phase compensation circuit 21 connected between the input and output of the output circuit 18 from a series connection circuit of a capacitor 19 and a resistor 20;
It is configured with.

In FIG. 3, signals inputted from signal input terminals 59 and 60 are inputted to positive-phase and negative-phase input terminals of a differential amplifier circuit 17, and a capacitor 19 and a resistor 20 are connected between the input and output terminals.
The signal is phase compensated via the gain circuit 18 to which the phase compensation circuit 21 consisting of the following is connected, and is output from the signal output terminal 61.

Now, the mutual conductance of the differential amplifier circuit 17 in FIG. 3 is expressed as g, 1. The output resistance is R1, the load capacitance related to the output terminal 61 is CL, the resistance value of the resistor 20 included in the phase compensation circuit 21 is R1, and the capacitance value of the capacitor 19 is CF.
Then, an equivalent circuit as shown in FIG. 4 is obtained, and by appropriately selecting the above-mentioned resistance value Rf and capacitance value C, phase-compensated input/output signal characteristics can be obtained.

[Problem to be solved by the invention]

In the conventional operational amplifier described above, since feedback is applied directly from the output terminal to the input side of the output circuit via the phase compensation circuit, the phase compensation function is affected by the load, and the feedback circuit is Since it is composed of a resistor and a capacitor, it has the disadvantage that when the frequency of the input signal becomes high, it becomes a feed forward, and an extra zero point is generated, making it impossible to perform sufficient phase compensation.

[Means to solve the problem]

The operational amplifier of the present invention includes a gain circuit and an output circuit that are sequentially connected in cascade to differential amplifier circuits corresponding to first and second signal inputs, and that are connected between the input and output of the gain circuit. The feedback circuit is configured to include a phase compensation circuit including a predetermined capacitance and a source follower circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIGS. 1(&) and (b) are circuit diagrams showing the first and second embodiments of the present invention, respectively, and FIG. 2 is an equivalent circuit diagram of the first and second embodiments.

As shown in FIG. 1(a), the first embodiment includes a differential amplifier circuit 1, a gain circuit 2, an output circuit 3, and an NMO3.
) - a source follower circuit 7 including a radiator 5 and a resistor 6; and a phase compensation circuit 8 including a capacitor 4 and the source follower circuit 7.

In FIG. 1(a), signals inputted from signal input terminals 51 and 52 are inputted to the positive phase and negative phase input terminals of the differential amplifier circuit 1, and a capacitor 4 and a source follower circuit 7 are connected between the input and output. The signal is outputted from the signal output terminal 54 via the output circuit 3 via the gain circuit 2 to which the phase compensation circuit 8 including the phase compensation circuit 8 is connected.

As in the case of the conventional example, the mutual conductance of the differential amplifier circuit 1 is g, 1, the output resistance is R5, and the parasitic capacitance on the output side is C! Furthermore, the mutual conductance of the source follower circuit 7 in the phase compensation circuit 8 is g. , when the output resistance is R8 and the capacitance value of the capacitor 4 is Ce, an equivalent circuit as shown in FIG. 2 is obtained. This equivalent circuit has a form in which the resistance value R1 of the resistor 20 in the conventional equivalent circuit shown in FIG. 4 is replaced by the mutual conductance g0 of the source follower circuit 7 and the output resistance R8. Therefore, it is clear that a predetermined phase compensated characteristic can be obtained as the input/output characteristics of the present operational amplifier. Furthermore, as a unique feature of the present invention, since a source follower circuit is interposed in the phase compensation circuit forming the feedback circuit, stable phase compensation characteristics that are not affected by the load on the output side, the input/output frequency, etc. can be realized.

Next, a second embodiment of the present invention will be described. As shown in FIG. 1(b), in this embodiment, the differential amplifier circuit 9
, a gain circuit 10 , an output circuit 11 , a PMO 3) a source follower circuit 1 including a transistor 13 and a resistor 14
5, a capacitor 12, and a phase compensation circuit 16 including the capacitor 12 and a source 7-oror circuit 15.

In this embodiment, the source follower circuit 7 configured using the NMOS transistor 5 in the first embodiment shown in FIG. This is an example in which the equivalent circuit is the same as that in the first embodiment, as shown in FIG. Therefore, as in the case of the first embodiment, stable phase compensation characteristics that are not affected by the load on the output side, the input/output frequency, etc. are realized as the input/output characteristics of the operational amplifier.

〔Effect of the invention〕

As described above in detail, the present invention provides an operational amplifier including a differential amplifier circuit, a gain circuit, and an output circuit.
By connecting a phase compensation circuit in which a predetermined source follower circuit and a capacitor are connected in series between the input and output of the gain circuit, stable phase compensation characteristics that are not affected by the load on the output side and the input/output frequency can be obtained. There is an effect.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1(a) and (b) are circuit diagrams of the first and second embodiments of the present invention, respectively, and FIG. 2 is an equivalent circuit diagram of the first and second embodiments of the present invention. Circuit diagram, Figure 3 is a circuit diagram of a conventional example,
FIG. 4 is an equivalent circuit diagram of the conventional example. In the figure, 1.9.17...differential amplifier circuit,
2, lO...gain circuit, 3.11.18...
...Output circuit, 4, 12.19... Capacity, 5
・・・・・・NMOS transistor, 6,14.20・
......-Resistor, 7,15... Source follower circuit, 8.16.21... Phase compensation circuit.

Claims (1)

[Claims] A gain circuit and an output circuit are sequentially connected to the differential amplifier circuit corresponding to the first and second signal inputs, and a predetermined feedback circuit is connected between the input and output of the gain circuit. An operational amplifier comprising a phase compensation circuit including a capacitance of 1 and a source follower circuit.