A programmable switched-capacitor A-DQS frequency downconverter for two-step channel selection wireless receiver

This paper presents a combined half-and full-delay switched-capacitor frequency downconverter with embedded channel selection function through a programmable analog-double quadrature sampling (A-DQS) technique. With such circuit operating in a complex low-IF wireless receiver back-end, the IF-to-baseband frequency down-conversion of the desired channel or its image can be effectively selected to the baseband to relax the settling time and phase noise requirements of the front-end frequency synthesizer. Moreover, such circuit also allows I/Q multiplexing for the following A/D converter and then minimizes the image problem due to I/Q mismatch. The prototype circuit is designed and verified in CADENCE^TM environment with the parameters of a 0.35-μm CMOS process.