An adaptive offset cancellation mixer for direct conversion receivers in 2.4 GHz CMOS

In this paper we present a new circuit design for a 2.4 GHz CMOS direct conversion mixer incorporating adaptive offset cancellation. The basic circuit structure is that of a Gilbert cell mixer. Offsets are cancelled by dynamically varying the bias on the loads, which are designed to provide constant impedance independent of the load cancellation current. The bias control is regulated via an adaptive dual-loop (gear-shifting) algorithm. Performance is good when canceling offsets of any realistic magnitude. The mixer has a gain of 6.4 dB, IIP3 of 17 dBm and noise figure of 17 dB.