A 0.18-$muhbox{m}$ CMOS GFSK Analog Front End Using a Bessel-Based Quadrature Discriminator With On-Chip Automatic Tuning

A fully integrated 2-MHz Gaussian frequency-shift keying (GFSK) analog front end for low-IF receivers is presented. The analog GFSK demodulation uses a Bessel-based quadrature discriminator and a differentiator-based data decision circuit, eliminating the need for analog–digital converters while enabling high sensitivity and large frequency offset tolerance. The analog front end consists of a fifth-order Butterworth low-pass prefilter, a seven-stage limiter, a quadrature discriminator with a fourth-order Bessel phase-shift network, a fourth-order Butterworth low-pass postfilter, and a differentiator-based data decision circuit. The prefilter, Bessel phase shifter, postfilter, and differentiator are built using identical $Gm{-}C$ cells and tuned across process variations with a single master–slave phase-locked loop. The GFSK analog front end is implemented in a 1.8-V 0.18-${rm mu}hbox{m}$ CMOS process, recovering 1-Mb/s input data from a 2-MHz GFSK signal with maximum frequency deviation of $pm$160-kHz, frequency offset tolerance from $-$ 38% to $+$ 47%, and input sensitivity of $-$53 dBm and consuming 7 mA of current.