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 (BPF) include Q-enhancement, gm-C and N-path. Q-enhancement has several disadvantages such as high area consumption due to inductors which do not obey process scaling, limited tuneability and poor dynamic range [2]. Main drawbacks of gm-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. However, N-path filters [6] have two main limitations: 1) The switch resistance R sw limits the ultimate rejection to R sw /(R sw +R s) (typically 16dB [4]) where R s is the source impedance; 2) Recent published N-path filters have only second order filtering, and higher orders have only been achieved by cascading[4], still rendering a " round " bandpass filter shape. This paper proposes a new method to increase the order of the BP filter while having a better pass-band