Current source/sink with high output impedance using bipolar transistors
AssigneeTexas Instruments Incorporated
InventorsMarco Corsi, William J. Bright, Martin Kithinji Kinyua
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Abstract
A circuit and method that provides a cascode current source/sink with high output impedance. In one example, the dependency on the external load is reduced by directing a compensation current corresponding to change in base current in the cascode (Q1) in an approach such that the compensation current cancels out the error of the cascode (Q1). In a further example, biasing circuitry (200) is included and arranged such that change in base current of the cascode (Q1) is detected and a corresponding current is summed at the emitter of the cascode (Q1) such that the collector current of the cascode (Q1) remains unchanged.
Claims16
A method for increasing output impedance of a current source/sink which includes circuitry for providing an output current to an external load, said circuitry including a first bipolar junction transistor (BJT) having a base, collector and emitter, said first BJT coupled in series with a second BJT having a base, collector and emitter, wherein said emitter of said first BJT is coupled to said collector of said second BJT and the external load is coupled between said collector of said first BJT and said emitter of said second BJT, said method comprising:
- detecting base current variance in said first BJT;
- and
- compensating for said detected base current variance by continuously applying a current to said first BJT emitter and said second BJT corresponding to the detected base current variation.
A device for increasing output impedance of a current amplifier which provide a current to an external load, the current amplifier having an input stage and an output stage, the output stage including a transistor having a base, collector and emitter in cascode with an output transistor having a base, collector and emitter, the fault device comprising:
- a means for detecting base current variance in said cascode transistor;
- and
- a means for compensating for said detected base current variance by continuously applying a variable current to the cascode transistor emitter and the output transistor collector, said variable current corresponding to the detected base current variation.
A current amplifier comprising:
- an input stage for providing a reference current;
- and
- an output stage having first circuitry operable to source an output current to an external load, said circuitry including a first bipolar junction transistor (BJT) having a base, collector and emitter, said first BJT coupled in series with a second BJT having a base, collector and emitter, wherein said emitter of said first BJT is coupled to said collector of said second BJT and the external load is coupled between said collector of said first BJT and said emitter of said second BJT;
- said output stage further having second circuitry coupled to said first BJT and said second BJT and operable to compensate for base current error in said first BJT by continuously applying a current corresponding to the base current error to said first BJT transistor emitter.
Dependencies are inferred from the claim text.