A 0.3-to-1.2GHz tunable 4th-order switched gm-C bandpass filter with >55dB ultimate rejection and out-of-band IIP3 of +29dBm

The trend towards reconfigurable receivers requires on-chip flexible filters that can replace dedicated, bulky and non-tunable filters (e.g., SAW and BAW [1]). Although BAW filters are compatible with silicon processes, their center frequency is sensitive to thickness variation of the piezoelectric material and the achievable tuneability is limited [1]. Other techniques to make RF on-chip band-pass filters (BPFs) include Q-enhancement, g
_m
-C and N-path. Q-enhancement approach has several disadvantages such as large area due to inductors which do not obey process scaling, limited tuneability and poor dynamic range [2]. Main drawbacks of g
_m
-C filters are the tradeoff between power consumption, quality factor, center frequency and dynamic range and the need for tuning circuitry [3]. Recently there has been renewed interest in the translational impedance conversion of N-path filters [4-6]. Due to the “transparency” of the passive mixer, baseband impedance is translated to frequencies around the clock frequency f
_lo
[7]. The interesting features of these filters are their direct tuneability with f
_lo
, higher quality factor compared to on-chip CMOS LC filters [2], high linearity and graceful scaling with process.