JPH11127037A - Cmos operational amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excess current from flowing through an output terminal of a push-pull CMOS operational amplifier even when a heavy load is connected to the output terminal. SOLUTION: A circuit to limit an output current is added to output TRs 9, 10 at both sink current and source current sides of an output circuit of the push-pull CMOS operational amplifier and even when a very heavy load is connected to the output, it is prevented that an excess current flows from the output TR 9 or 10 at the sink current or the source current side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CMOS monolithic IC operational amplifier and a CMOS monolithic IC.
The present invention relates to a device using an operational amplifier converted to C.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional push-pull type CMOS operational amplifier. The output of the differential amplifier circuit 101 is connected to the gate of the output transistor 10 and drives the output transistor 10 directly. Also, the differential amplifier circuit 10
The output of 1 is also connected to the gate of the transistor 5, and distributes the current of the constant current source 12 to the transistors 5 and 6 according to the magnitude of the output voltage value of the output of the differential amplifier circuit 101. When the output voltage value of the differential amplifier circuit 101 is large and the gate voltage value of the transistor 10 is large, the transistor 5
The current flowing through the transistor 6 increases, and the current flowing through the transistor 6 decreases. The transistor 6 and the transistor 7 form a current mirror, and a current flows through the transistor 6 and the transistor 7 according to the size ratio (the ratio of the gate width / gate length) of the transistor 6 and the transistor 7,
The current flowing through the transistor 7 flows through the transistor 8. The transistor 8 and the transistor 9 constitute a current mirror, and the transistor 8 and the output transistor 9
, An output current flows according to the size ratio between the transistor 8 and the output transistor 9.

[0003]

In a CMOS operational amplifier having a push-pull type output circuit, if the load connected to the output is very heavy and a large output current flows through the output transistor 9 in FIG. Differential amplifier circuit 1
01 is small, and the gate voltage values of the transistor 5 and the output transistor 10 are also small. For this reason, most of the current of the constant current source 12 flows through the transistor 6, and a current corresponding to the size ratio flows through the output transistor 9 via the current mirror to become an output current. Since the maximum current flowing through the transistor 6 is limited by the constant current source 12, an output current exceeding a certain current does not flow through the output transistor 9.

However, when a large output current flows through the transistor 10, the output transistor 10 is directly driven by the output of the differential amplifier 101,
Output transistor 1 when the load current becomes very large
There is a problem that an excessively large output current flows to 0, and the element, the IC, the package and the device using the push-pull type CMOS operational amplifier are destroyed by the overcurrent and the heating due to the overcurrent.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a circuit for limiting the output current of an output transistor to both a sink current side and a source current side of an output circuit of a push-pull type CMOS operational amplifier. To prevent an excessive current from flowing to the output transistor on both the sink current side and the source current side.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The maximum value of the output current of an output transistor is set between the output terminal of a differential amplifier circuit of a CMOS operational amplifier having a push-pull type output circuit and the gate of an output transistor of a push-pull type output circuit. A means for limiting is provided. Even when the output voltage value of the differential amplifier circuit is very large, the gate voltage of the output transistor is limited to a certain value or less so that an excessive output current does not flow. As a result, an excessive output current flows to the output transistor, and the element, the IC, the package, and the IC using the push-pull type CMOS operational amplifier are generated by the overcurrent and the heating by the overcurrent.
Prevents the device using the device from being destroyed.

[0007]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a push-pull type CMOS operational amplifier according to the present invention. An output current limiting circuit 13 is provided between the differential amplifier circuit 102 and the output transistor 10. In the output current limiting circuit 13, the input voltage value and the output voltage value are usually proportional values. However, the output current limiting circuit 1
When the input voltage value to the input terminal 3 becomes very large, the output voltage value rises only to a certain constant value. Output transistor 1 so that output current does not flow
The gate voltage of 0 can be limited. Similarly, there is an output current limiting circuit 14 between the differential amplifier circuit 102 and the output transistor 9. Similarly, the output current limiting circuit 14
Usually, the input voltage value and the output voltage value are proportional values. However, when the input voltage value to the output current limiting circuit 14 becomes a very small value, the output voltage value decreases only to a certain constant value, so that the output level of the differential amplifier circuit 102 is low. Even so, the gate voltage of the output transistor 9 can be limited so that an excessive output current does not flow.

FIG. 3 shows an example of a detailed circuit diagram of the block diagram shown in FIG. The output of the differential amplifier 101 enters the gate of the transistor 5 and the gate of the transistor 1. The transistor 1 distributes the current of the constant current source 11 to the transistor 1 and the transistor 2 according to the output voltage value of the differential amplifier circuit 101. When the output voltage value of the differential amplifier circuit 101 is large, the gate voltage of the transistor 1 is large, so that the current flowing through the transistor 1 is small,
The current flowing through becomes larger. The transistor 2 and the transistor 3 form a current mirror. A current flows through the transistor 2 and the transistor 3 according to the size ratio of the transistor 2 and the transistor 3, and the current flows through the transistor 4. Transistor 4 and output transistor 1
0 forms a current mirror, and an output current flows through the transistor 4 and the output transistor 10 according to the size ratio between the transistor 4 and the output transistor 10. When the output voltage value of the differential amplifier circuit 101 is a larger value, the current flowing through the transistor 1 is reduced, so that the current flowing through the transistor 2 increases. Even when a very heavy load is connected, the current flowing through the transistor 2 at most is the current flowing through the constant current source 11, and the current according to the size ratio is output via the current mirror to the output transistor 1.
Since the current flows to 0, the maximum value of the output current value is limited, and an excessive output current does not flow.

Similarly, the output current of the output transistor 9 is
The current of the constant current source 12 is distributed to the transistors 5 and 6 by the output of the differential amplifier circuit 101. When the output voltage value of the differential amplifier circuit 101 is small, the gate voltage value of the transistor 5 is also small, the current flowing through the transistor 5 is small, and the current flowing through the transistor 6 is large.
The transistor 6 and the transistor 7 form a current mirror. A current according to the size ratio of the transistor 6 and the transistor 7 flows through the transistor 6 and the transistor 7, and a current flowing through the transistor 7 flows through the transistor 8. The transistor 8 and the output transistor 9 form a current mirror, and a current flows through the transistor 8 and the output transistor 9 according to the size ratio of the transistor 8 and the output transistor 9. Even when a very heavy load is connected, the current flowing through the transistor 1 at most is the current flowing through the constant current source 12, and the current corresponding to the size ratio is output via the current mirror to the output transistor 9.
Output current value is limited to the maximum value,
Excessive output current does not flow.

Although the description of FIG. 3 has been made only for the Nch output transistor, when the Pch transistor side is directly driven by the output of the differential amplifier circuit, a circuit for limiting the output current to the Pch side. Can also be added. The present invention provides an output circuit of a CMOS type operational amplifier using a push-pull type output circuit, in which the output current is limited on both sides of a source current side and a sink current side. Is not limited to the circuit type shown in FIG. The present invention also provides
C using a push-pull type output circuit that limits the output current on both the source current side and the sink current side of the output circuit
The present invention is also applied to an IC using a MOS operational amplifier and a device using this IC.

[0011]

A CMOS having a push-pull type output circuit
In an operational amplifier, a limit is set on the maximum value of the output current of the output transistor on both sides of the sink current side and the source current side. And I using the push-pull type CMOS operational amplifier
The device using C is prevented from being destroyed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an output circuit of a push-pull operational amplifier of the present invention.

FIG. 2 is an explanatory diagram of an output circuit of a conventional push-pull operational amplifier.

FIG. 3 is an example of a detailed circuit diagram of FIG. 1;

[Explanation of symbols]

 1-8 MOS transistor 9, 10 output transistor 11, 12 constant current source 13, 14 output current limiting circuit 101, 102 differential amplifier circuit

Claims (1)

[Claims] 1. A CMOS operational amplifier having a push-pull type output circuit as an output stage comprising a source current side output transistor for supplying a current to an output terminal and a sink current side output transistor for taking in a current from the output terminal. A circuit for limiting the output current flowing to both the sink current side and the source current side is provided.
A CMOS operational amplifier that prevents an excessive current from flowing to an output transistor even when a heavy load is connected to either output on the source current side.