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US 5,394,079 AGranted
Current mirror with improved input voltage headroom
AssigneeNational Semiconductor Corporation
InventorWilliam D. Llewellyn
Life of this patent
Estimating the term…
Abstract
A novel current mirror is taught which provides improved input voltage headroom. The current mirror provides for the ratioed current mirroring of an input current supplied by a current source while providing an increased voltage level to that current source as compared with prior art current mirrors. This provides a significant improvement over prior art current mirrors which are likely to provide an insufficiently high voltage level to the current source to allow its proper operation, particularly with the trend toward lower supply voltages.
Claims25
A current mirror comprising:
- a first power supply terminal for receiving a first supply voltage;
- a second power supply terminal for receiving a second supply voltage;
- a first mirror transistor having a first current handling terminal coupled to a first one of said 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 having a first current handling terminal coupled to said first one of said power supply terminals, a second current handling terminal serving as an output terminal for providing a mirrored output current as a function of said input current to be mirrored, and a control terminal coupled to said control terminal of said first mirror transistor;
- and
- a level shift device comprising a level shift transistor having a first current handling terminal coupled to said first power supply terminal, a second current handling terminal coupled to said commonly coupled control terminals of said first and second mirror transistors, and a control terminal coupled to said input terminal.
3 more elements
A current mirror comprising:
- a first power supply terminal for receiving a first supply voltage;
- a second power supply terminal for receiving a second supply voltage;
- a first mirror transistor having a first current handling terminal coupled to a first one of said 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 having a first current handling terminal coupled to said first one of said power supply terminals, a second current handling terminal serving as an output terminal for providing a mirrored output current as a function of said input current to be mirrored, and a control terminal coupled to said control terminal of said first mirror transistor;
- and
- a level shift device comprising a level shift transistor having a first current handling terminal coupled to said first power supply terminal, a second current handling terminal coupled to said commonly coupled control terminals of said first and second mirror transistors, a control terminal coupled to said input terminal, and a bulk region connected to a bias voltage between said first and second supply voltages.
3 more elements
A method for mirroring current comprising the steps of:
- providing a first supply voltage;
- providing a second supply voltage;
- providing a current which is to be mirrored through a first mirror transistor;
- providing an output current from a second mirror transistor as a function of said current to be mirrored;
- and
- providing a voltage level shift between a control terminal of said first mirror transistor and a current handling terminal of said first mirror transistor for receiving said current to be mirrored, wherein said step of providing a voltage level shift comprises the step of:
- applying a bipolar transistor base-emitter voltage drop between said current handling terminal of said first mirror transistor for receiving said current to be mirrored and said control terminal of said first mirror transistor and without causing emitter-collector current of said bipolar transistor to flow through said control terminal of said first mirror transistor.
4 more elements
A method for mirroring current comprising the steps of:
- providing a first supply voltage;
- providing a second supply voltage;
- providing a current which is to be mirrored through a first mirror transistor;
- providing an output current from a second mirror transistor as a function of said current to be mirrored;
- and
- providing a voltage level shift between a control terminal of said first mirror transistor and a current handling terminal of said first mirror transistor for receiving said current to be mirrored, wherein said step of providing a voltage level shift comprises the step of:
- applying an MOS transistor gate-source voltage drop between said current handling terminal of said first mirror transistor for receiving said current to be mirrored and said control terminal of said first mirror transistor and without causing source-drain current of said MOS transistor to flow through said control terminal of said first mirror transistor.
4 more elements
Dependencies are inferred from the claim text.