GILBERT CELL MIXER WITH LINEAR TRANSCONDUCTOR STAGE

摘要

A multiplier is provided, for example, for use as a mixer in a modulator of a radio frequency transmitter. The multiplier multiplies a first alternating signal of constant amplitude by a second signal, for example, in the form of a carrier wave from a local oscillator. The multiplier comprises a transconductance stage for converting the first signal to a differential output current and a current switching stage for switching the differential output current in accordance with the second signal. The transconductance stage comprises a plurality of offset pairs (10-13) of transistors, whose inputs and outputs are connected in parallel. The switching stage comprises cross-coupled pairs of transistors (16-19) which, together with the transconductance stage, form a Gilbert cell. The relative gains of the transistors (10-13) of each offset pair are such that a minimum in the third harmonic distortion characteristic of the multiplier occurs substantially at the amplitude of the first signal.