Differential pair gain control stage

摘要

A "gain control differential pair" (GCDP) conducts current in response to a differential drive signal, with the gain of a signal path formed via the current circuit of one of its transistors controlled by the drive signal. The GCDP is preferably driven with a drive circuit that receives a symmetrical input signal and produces an offset differential drive signal which has the effect of keeping one of the GCDP's transistors turned off over a wider portion of a symmetrical input signal's voltage range, thereby reducing GCDP-caused noise. One or more GCDPs are implemented as part of a Gilbert mixer to regulate the amount of RF current that flows between the mixer's output and input stages, which eliminates the need to provide gain control in other circuits fed by the mixer. When driven with an offset drive signal, the Gilbert mixer simultaneously provides gain control, low distortion, low power consumption and excellent LO/RF isolation.