Operational amplifier operable with high performance even at a low voltage
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorShiro Dosho
Life of this patent
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Abstract
An operational amplifier attaining a class-AB operation with a low voltage power supply. The operational amplifier has an output buffer circuit including transistors of opposite polarity serially connected with an output there between. A first differential current amplifier and a first current mirror circuit drive one of the transistors. A level shifter that includes a second differential current amplifier, a second current mirror circuit and a current aliasing circuit drives the other transistor. The current aliasing circuit is operated at a very low voltage. With this configuration, the currents that flow through the transistors have different values, resulting in a differential current being output from the output between the transistors.
Claims12
A class-AB operational amplifier comprising:
- a first power supply having a predetermined voltage;
- a second power supply having a voltage different from said predetermined voltage;
- an output buffer circuit including a serial connection of a transistor of a first polarity connected with said first power supply, a transistor of a second polarity connected with said second power supply and an output terminal provided at a node between said transistors, said transistors being driven by using an input differential signal;
- a first differential current amplifier including transistors of a predetermined polarity for receiving the differential signal for amplification and driving said transistor of the second polarity;
- and
- a level shifter for generating a voltage to be supplied to a current control terminal of said transistor of the first polarity in order to drive said transistor of the first polarity,
- wherein said level shifter includes:
- a constant current source for supplying a constant current;
- a second differential current amplifier including transistors of the same polarity as said transistors included in said first differential current amplifier for receiving the constant current from said constant current source and receiving the differential signal for amplification;
- a current aliasing circuit connected between said second differential current amplifier and said second power supply for looping an output current of said second differential current amplifier;
- and
- a current mirror circuit connected between said first power supply and said current aliasing circuit for allowing a current having a current value based on an output current of said current aliasing circuit to flow and to be supplied to the current control terminal of said transistor of the first polarity.
Dependencies are inferred from the claim text.