GAIN CONTROL AMPLIFIER, VARIABLE GAIN AMPLIFIER AND AUTOMATIC GAIN CONTROL AMPLIFIERS INCLUDING DIFFERENTIAL CIRCUIT TRANSISTORS AND CURRENT SPLITTER

摘要

A gain control amplifier includes an input diffential circuit having a pair of transistors, the emitters of which are coupled via a pair of emitter resistors. The input differential circuit includes a current sink for providing an operating current. With variation of the operating current, the gain control amplifier's gain is varied. Two emitter coupled differential amplifiers are connected to the input diffential circuit having a current sink. A current flowing in the transistors of the emitter coupled differential amplifier and the input differential circuit is split by an additional emitter coupled differential circuit having a current sink. A current splitting factor is controlled in response to the voltage difference between the collectors of the two transistors of the two emitter coupled differential amplifiers. Since the relatively small currents flow in the emitter resistors, noise caused thereby is relatively low. Thus, it provides a wide input dynamic range with low noise. The gain control amplifier is used in a variable gain amplifier and an automatic gain control amplifier.