Reciprocal Mixing Noise Supression in Mixer Based Wireless Receivers

Reciprocal mixing (RM) noise presents a significant challenge in wireless receivers, particularly in the presence of strong out-of-band (OOB) blockers that degrade the in-band noise floor through convolution with local-oscillator (LO) phase noise (PN), thereby increasing the effective noise figure (NF). N-path mixers provide inherent filtering and frequency translation properties; however, they remain sensitive to RM noise arising from both external LO PN and internal PN from clock generation circuitry. This motivates the development of architectures that suppress RM while preserving the fundamental advantages of N-path mixers. The research focuses on N-path mixer architectures that decouple the RM transfer function from the desired signal transfer function, enabling digital-domain RM cancellation.

The first investigated architecture exploits controlled LO phase delay to enable RM cancellation in a 65 nm CMOS N-path mixer implementation. The design achieves 16 dB of RM cancellation due to external LO PN, while incurring only a 2 dB NF penalty. These results demonstrate the effectiveness of the approach in improving blocker resilience while maintaining low noise degradation.

The 65 nm implementation was limited by OOB blocker B1dB and internal LO PN that could not be canceled. To address this, an improved N-path mixer was implemented in 180 nm SOI using resonant LO buffers instead of square-wave clocks to reduce internal PN and enhance linearity. Post-layout simulations show tolerance to a 20 dBm OOB blocker with only 2–3 dB NF degradation. Compared to the 65 nm design, the SOI implementation withstands stronger blockers while maintaining similar noise performance and achieves ~2× better LO driver power efficiency for a given internal PN level at 1 GHz, with greater benefits expected at higher frequencies.

M.Sc. student under the supervision of Prof. Emanuel Cohen.