A low-power Gm-R-C image rejection filter for complex low-IF receiver

In this paper, a 1^st-order G_m-R-C complex filter cell for image rejection in low-IF receivers is proposed. The cell adopts low-power fully differential G_m-cells with RC load to perform low-pass filtering for the input I/Q signals. Frequency translation is realized by two additional differential G_m cells through directly cross-adding relevant currents. Based on the proposed 1^st-order cell, a 4^th-order Butterworth complex filter with center frequency at 300 KHz and bandwidth of 160 KHz is designed in 0.18 μm CMOS technology. Simulated results show that the filter achieves an image rejection ratio of 62 dB, an in-band SFDR of 58.9 dB, a pass-band gain of 18 dB, and an input referred noise of 19.4 μV_rms, while consuming only 593 μA from a 2.7 V supply.