Widely Tunable 4th Order Switched Gm -C Band-Pass Filter Based on N-Path Filters

Abstract—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 mm2.