A sharp programmable passive filter based on filtering by Aliasing

This paper presents the 1^st integrated circuit demonstration of Filtering by Aliasing (FA). FA is a recent technique that uses linear periodically time varying (LPTV) analog circuitry prior to a sampler to provide a desired CT-to-DT transfer function. Such LPTV signal processing offers far superior programmability and performance relative to LTI design. The presented IC applies FA to a single-pole passive RC filter. The resistor, realized as a switched resistor ladder, is continuously varied using on-chip digital control while the output is sampled at a baseband rate. Measured CT-to-DT responses show tunable-bandwidth filter roll-off better than 60 dB/dec, stop-band suppression up to 60 dB, tunable carrier up to 800 MHz, up to 31 dBm out-of-band IIP3, and harmonic rejection.