The PT-28E is a differential-output receiver module for 28/56 GBd PAM-4 transmission system receive applications. It couples a back-illuminated PIN photodiode, usable from 1200 nm to 1650 nm, with an internal transimpedance gain stage. This combination produces a receiver with a 30 GHz bandwidth with no peaking and conversion gain of 1900 V/W. The receiver can be operated in a fixed maximum-gain, AGC, or SPI mode. SPI mode offers greater control of the bandwidth and gain through the receiver's SPI digital controls. The compact 12-pin package is available with dual GPPO™ output connectors in a compact butterfly package with single-mode fiber input.