A Stochastic Variable Gain Amplifier Adaptation for PAM-4 signaling

This paper presents a stochastic variable gain amplifier (VGA) adaptation method for a four-level pulse amplitude modulation (PAM-4) signaling. Two error samplers and three data samplers are used per clock, and two sets of such samples from two sequential unit intervals (UIs) are detected. The weighted summation of 36 symbol histograms is used for VGA adaptation. The weight of each symbol is calculated using Bayes’ theorem. The stochastic VGA adaptation enables settlements to the lock point even with a closed eye while a sign-sign least mean square (SSLMS) algorithm fails to lock. Even though the number of error samplers is reduced for high clocking power efficiency, the proposed stochastic adaptation utilizes eight more transitions than the SSLMS, resulting in a shorter adaptation time compared with the SSLMS algorithm.