Using Analog Complex Mixers for Low-IF Mixing

IQ mixers and complex mixers are both used to cancel the image band signal. In this paper, we analyse a complex IF sub-THz receiver architecture aimed for splitting a multi-GHz baseband signal into narrower sub-bands for easier A/D conversion. The architecture consists of a normal IQ direct downconversion, followed by complex mixers to center the chosen sub-carriers to DC. Image rejection versus mismatch errors is calculated both analytically and on system and circuit-level simulations. It was seen that the image rejection is dominated by the IQ downconversion stage. It is demonstrated that the mismatches in the IQ stage can be corrected digitally by weighted summing of the digital sub-bands.