Current mirror with improved input voltage headroom

Details Current mirror with improved input voltage headroom Current mirror with improved input voltage headroom

1994-12-30

1996-05-28

Wong, Peter S.

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

323316, G05F 320

Patent

active

055214908

ABSTRACT:
A current mirror includes a first power supply terminal for receiving a first supply voltage and a second power supply terminal for receiving a second supply voltage. A first mirror transistor has a first current handling terminal, coupled to the first power supply terminals, a second current handling terminal serving as an input terminal for receiving an input current to be mirrored, and a control terminal. A second mirror transistor has a first current handling terminal coupled to the first power supply terminal, a second current handling terminal serving as an output terminal for providing a mirrored output current to a load as a function of the input current to be mirrored, and a control terminal coupled to the control terminal of the first mirror transistor. In a first embodiment, a level shift transistor has a first current handling terminal coupled to the first power supply terminal, a second current handling terminal, and a control terminal coupled to the input terminal. The level shift transistor increases the amount of input voltage headroom which would otherwise be available to operate a current source which provides the input current to be mirrored. In further embodiments, a first biasing resistance element is coupled between the first power supply terminal and the first mirror transistor control terminal, and a second biasing resistance element is couples the commonly coupled control terminals of the first and second mirror transistors to the second current handling terminal of the level shift transistor. The first and second biasing resistance elements ensure that input voltage headroom, while increased, remains low enough to keep the first current mirror transistor operating in a saturation region.

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O. Schade, Jr., "Advances in BIMOS Integrated Circuits," RCA Review, vol. 39, Jun. 1978, pp. 250, 254-261, 270-271.

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