Offset correction for down-conversion mixers

Abstract

A direct conversion receiver includes a detector that provides a measure of bias offset that is caused by component mismatches in the direct conversion mixer, and a corrective network that reduces the bias offset based on this measure. The direct conversion mixer demodulates a radio-frequency (RF) input signal via mixing with a local-oscillator (LO) signal to provide a differential baseband output signal. A differential peak detector compares the peak signal value at each side of the mixer's differential output, and a differential integrator averages the difference between these peak signal values to provide the measure of bias offset. The corrective network adds a correction offset to each of the local oscillator local oscillator paths on each of the switching pairs that provide the differential output, but opposite to the local oscillator connections. By applying the correction offset to the opposing transistor in each pair, the difference in switching time between the pairs is reduced, and, correspondingly, the differential-mode leakage from the local oscillator to the RF input stage is reduced.