Analysis and Design of I/Q Charge-Sharing Band-Pass-Filter for Superheterodyne Receivers

A complex quadrature charge-sharing (CS) technique is proposed to implement a discrete-time band-pass filter (BPF) with a programmable bandwidth of 20-100 MHz. The BPF is part of a cellular superheterodyne receiver and completely determines the receiver frequency selectivity. It operates at the full sampling rate of up to 5.2 GHz corresponding to the 1.2 GHz RF input frequency, thus making it free from any aliasing or replicas in its transfer function. Furthermore, the advantage of CS-BPF over other band-pass filters such as N-path, active-RC, G_m-C, and biquad is described. A mathematical noise analysis of the CS-BPF and the comparison of simulations and calculations are presented. The entire 65 nm CMOS receiver, which does not include a front-end LNTA for test reasons, achieves a total gain of 35 dB, IRN of 1.5 nV/√(Hz), out-of-band IIP3 of +10 dBm. It consumes 24 mA at 1.2 V power supply.