A design methodology for synthesis of active N-path bandpass filters is introduced. Based on this methodology, a 0.1to-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 outof-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 IIP 3 (∆f = +50 MHz), an out-of-band 1dB blocker compression point B 1dB,CP of +7 dBm (∆f = +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 dBm at a clock frequency of 1 GHz. The proposed filter only consists of inverters, switches and capacitors and therefore it is friendly with process scaling.

A widely tunable 4th order BPF based on the subtraction of two 2nd order 4-path passive-mixer filters with slightly different center frequencies is proposed. The center frequency of each 4-path filter is slightly shifted relative to its clock frequency (one upward and the other one downward) by a gm-C technique. Capacitive splitting of the input signal is used to reduce the mutual loading of the two 4-path BPFs and increase their quality factors. The filter is tunable from 0.4 GHz to 1.2 GHz with approximately constant bandwidth of 21 MHz. The in-band 1-dB compression point of the filter is −4.4 dBm while the in-band IIP3 of the filter is +9 dBm and the out of band IIP3 is +29 dBm (∆f= +50 MHz). The ultimate rejection of the filter is >55 dB and the NF of the filter is 10 dB. The static and dynamic current consumption of the filter are 2.8 mA from 2.5 V and 12 mA from 1.2 V, respectively (at 1 GHz). The LO leakage power to the input port is <−60 dBm. The filter has been fabricated in CMOS LP 65 nm technology and the active area is 0.127 mm 2 .

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Radio receivers should be robust to large out-of-band blockers with small degradation in their sensitivity. N-path mixers can be used as mixer-first receivers [1] with good linearity and RF filtering [2]. However, 1/f noise calls for large active device sizes for IF circuits and high power consumption. The 1/f noise issue can be relaxed by having RF gain. However, to avoid desensitization by large out-ofband blockers, a bandpass filter (BPF) with sharp cut-off frequency is required in front of the RF amplifiers. g m -C BPFs suffer from tight tradeoffs among DR, power consumption, Q and f c . Also, on-chip Q-enhanced LC BPFs [3] are not suitable due to low DR, large area and non-tunability. Therefore, bulky and nontunable SAW filters are used. N-path BPFs offer high Q while their center frequency is tuned by the clock frequency [2]. Compared to g m -C filters, this technique decouples the required Q from the DR. The 4-path filter in [4] has only 2 ndorder filtering and limited rejection. The order and rejection of N-path BPFs can be increased by cascading [5], but this renders a "round" passband shape. The 4 th -order 4-path BPF in [6] has a "flat" passband shape and high rejection but a high NF. This work solves the noise issue of [6] while achieving the same outof-band linearity and adding 25dB of voltage gain to relax the noise requirement of the subsequent stages.