Design of Active N-path Filters

A design methodology for synthesis of active N-path bandpass filters is introduced. Based on this methodology, a 0.1-to-1.2 GHz tunable 6th-order N-path channel-select filter in 65 nm LP CMOS is introduced. It is based on coupling N-path filters with gyrators, achieving a “flat‿ passband shape and high out-of-band linearity. A Miller compensation method is utilized to considerably improve the passband shape of the filter. The filter has 2.8 dB NF, +25 dB gain, +26 dBm wideband IIP₃ ( MHz), an out-of-band 1 dB blocker compression point B of +7 dBm (Δf = +50 MHz) and 59 dB stopband rejection. The analog and digital part of the filter draw 11.7 mA and 3–36 mA from 1.2 V, respectively. The LO leakage to the input port of the filter is ≤-64 dBmat a clock frequency of 1 GHz. The proposed filter only consists of inverters, switches and capacitors and therefore it is friendly with process scaling.