Amplifier/oscillator circuit with common-emitter amplifier and differential amplifier

摘要

An amplifier/oscillator circuit is provided, which makes it possible to interconnect a differential amplifier with a common-emitter amplifier without any coupling capacitor. This amplifier circuit is comprised of (a) a common-emitter amplifier including a first bipolar transistor; (b) a first level converter for converting a dc level of the first output signal to a first dc level; (c) a second level converter for converting a dc level of the second output signal to a second dc level; and (d) a differential amplifier including first and second input terminals and first and second output terminals. An input signal is applied to abase of the first bipolar transistor, thereby producing first and second output signals. The first and second output signals of the common-emitter amplifier are derived from the base and collectors of the first bipolar transistor, respectively. Dc levels at the first and second input terminals of the differential amplifier are equal to the first and second dc levels, respectively. The first and second output signals of the common-emitter amplifier are applied to the first and second input terminals of the differential amplifier through the first and second level converters, thereby producing first and second output signals at the first and second output terminals, respectively.