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

摘要

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 $g_m$-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 $-$4.4 dBm while the in-band IIP$_3$ of the filter is ${+}$9 dBm and the out-of-band IIP$_3$ is ${+}$ 29 dBm ($Delta 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$^2$ .