Ultra high gain amplifier

摘要

An amplifier has an output buffer having an input coupled to the second outputs of the first and second current mirrors for receiving the biasing current and having an output for providing an amplified drive current. The output buffer includes a first transistor of a first type having its base coupled to the input of the output buffer and to the base of a first transistor of a second type. The emitter of the first transistor of a first type coupled to the base of a second transistor of a second type, and a collector. The emitter of the first transistor of the second type is coupled to the base of a second transistor of the first type. The emitter of the second transistor of the first type is coupled to the emitter of the second transistor of the second type and to the output of the buffer. First and second current mirrors of complementary transistor types provide a reference current and a biasing current in response to a programming current and a feedback current. First and second current sources of complementary transistor types provide a supply current to the output buffer. The supply current is proportional to the reference current from the current mirrors. First and second cascode transistors maintain a substantially constant voltage between the collector and base of the first transistors of the first and second type of the output buffer. The emitter of the first cascode transistor is coupled to the collector of the first transistor of the first type of the output buffer. The emitter of the second cascode transistor is coupled to the collector of the first transistor of the second type. Voltage sources coupled between the base of the cascode transistors and the emitter terminals of the first transistors of the first and second type of the output buffer maintain substantially constant voltages between the base and collector of the first transistors of the output buffer. First and second feedback circuits coupled to the first transistors of the output buffer provide to the current mirrors feedback currents indicative of the biasing current drawn by the first transistors of the first and second types of the output buffer.