A 50Gb/s Burst-Mode NRZ Receiver with 5-Tap FFE, 7-Tap DFE and 15ns Lock Time in 28nm CMOS for Symmetric 50G-PON

With the growing demand for broadband services, the 50G passive optical network (PON) has become the future direction of optical access networks. As the baud rate rises to 50G, the limited bandwidth of photonic devices and chromatic dispersion degrade the signals more severely. In [1] a 41-tap feedforward equalization (FFE) is used to handle the complex inter-symbol interference (lSI). Meanwhile, in upstream PON, multiple optical network units (ONUs) transmit data to one optical line terminal (OLT) in burst mode, requiring OLTs to respond rapidly. In [2] a burst-mode receiver with 6.8ns CDR lock time is proposed, but it only adopted 1-tap decision-feedback equalization (DFE), which is inadequate to achieve reliable communication in a 50G-PON system. In addition, it utilized a p-i-n photodiode, in contrast to the avalanche photodiode (APD) preferred in ITU-T 50G-PON standards [3] due to its high conversion gain. However, APD and the low optical power in 50G-PON introduce more noise [4]. To achieve burst reception under large lSI and poor SNR in symmetric 50G-PON systems, this work proposes a 50Gb/s burst-mode NRZ Receiver in 28nm CMOS with 5-tap FFE including 3 pre taps and 1 post tap and 7-tap DFE including 4 floating taps ranging up to 16th post-cursor. Edge equalization is realized for accurate fast-lock, achieving a lock time of 15ns.