A wideband digital receiver with hard-switching mixers for cognitive radio

Among the primary challenges of designing a flexible and efficient wideband receiver for cognitive radio (CR) are harmonic distortion caused by the hard-switching commutating mixers, the need for wide tuning range frequency synthesizer to span the frequency band of interest, and the use of power-hungry high-speed analog-to-digital converters to reduce the sensing time. In this paper, the harmonic mixing process in wideband receivers is viewed as a multi-user access system in communications. Based on this perspective, a digital equalizer is developed to minimize harmonic distortion in the signal path, reduce the tuning range of the frequency synthesizer, and enable wider spectrum sensing. Compared to the analog harmonic-reject mixers in existing wideband receivers, the proposed receiver achieves significantly improved energy detection sensitivity while enabling parallel sensing of multiple harmonic signals and relaxing the frequency synthesizer tuning range requirement.