Frequency/Code-Domain Filtering Using Walsh-Function Sequence Based N-path Filters

Abstract

Applying orthogonal sequences to N-path filters promises reconfigurable select/reject filtering of signals based on their spatial, spectral and code-domain properties. Achieving code and frequency-domain notch filtering using inductors instead of capacitors has been challenging due to parasitics and self-resonance associated with large off-chip inductors. In this work, N-path frequency/code-domain reject and select filtering is demonstrated using N-path switching with passive inductors. A cascaded inductor approach and differential N-path filtering is used to overcome inductor parasitics and enable GHz operation. A 65-nm CMOS prototype of a code-domain notch filter followed by a code-domain select receiver demonstrates 0.5 GHz to 1.0 GHz operation with 26 dB blocker filtering with 8 dBm power handling, while consuming 60 mW (at 1 GHz LO) and occupying 1.2 mm2 of die area.