A harmonic rejection mixer robust to RF device mismatches

Harmonic rejection (HR) mixers are key building blocks in wideband receivers such as TV tuners and software-defined radio receivers employing low-IF or direct downconversion. In TV tuners, in-band HR in excess of 72dB is desired. A mixer capable of high harmonic-rejection ratio (HRR) is needed to relax the requirements on pre-mixer RF filters, which are expensive and bulky. HRR for conventional HR mixers [1] is limited by mismatches amongst devices operating at RF frequencies (shown in Fig. 3.8.1). Reducing mismatches by increasing device area to achieve high HRR comes at a severe cost of power, area and RF bandwidth. This matching requirement at RF frequencies limits the achievable HRR to be only between 30 and 40dB [2,3]. Recently, two-stage HR mixers have been proposed [4]. While [4] has reduced gain errors, phase errors that limit the achievable HRR are still determined by device matching at RF frequencies.