An IF Bandpass Filter Based on a Low Distortion Transconductor

In this paper, a linearity improvement technique is proposed for a low-distortion G_m-C bandpass filter operating in high IF ranges. The proposed transconductor eliminates G_m" value at the output by superposing the opposite non-linear behaviors of two differential structures in parallel. For the bandpass filter, instead of conventional biquad structure, a resonant-coupling structure is adopted for a flat frequency response which is insensitive to process and temperature variations. Fabricated in 65 nm CMOS process, the implemented 80 MHz bandpass filter shows a flat bandpass characteristic with 0.1 dB ripple, third-order harmonic rejection of 27 dB, IIP3 of -2 dBm, and NF of 21.5 dB, while consuming 11 mA from 1.2-V supply. The filter occupies the chip size of 0.5 × 0.5 mm².