A PAM-4 adaptive analog equalizer with decoupling control loops for 25-Gb/s CMOS serial-link receiver

PAM-4 signaling is an effective solution for high-speed CMOS serial-link transceivers, but it suffers from the difficulty of signal regeneration in analog front-end owning to its multi-level characteristics. An adaptive analog equalizer with decoupling control loops is proposed to address the nonlinearity of amplifiers. A low-frequency gain invariant equalizer and a golden signal generator are designed to serve boost and swing control loops, respectively. An integrating charge pump is employed to improve the convergence performance of receiver. Transistor-level simulation results show that the proposed adaptive analog equalizer in 40-nm CMOS technology can recover 25 Gb/s random data transmitted over a 29.8 inches Megtron6 printed circuit board (PCB) copper channel.