I. Introduction
Transimpedance amplifiers (TIAs) are the front-end device in optical receivers, after the photodiode, where they need to comply with stringent requirements in terms of high TI gain, bandwidth, and sensitivity, typically limiting the overall performance of the link. For the prospective standardization of 400 Gb/s Ethernet, future data centers will require a minimum speed of 100 Gb/s/lane to convey economically feasible products [1], which calls for the development of new low-power, high-performance receivers featuring above 70-GHz analog bandwidth [2]. Silicon-based solutions will be the preferred implementation platform for such receivers, so as to reduce cost and installation effort. Among them, SiGe BiCMOS technologies are best suited to address the upcoming challenges, demonstrating high transconductance and better noise performance over a wide bandwidth compared to their CMOS counterparts. BiCMOS TIA implementations that meet such speed requirements resort to simple TIA stages featuring very high bandwidth and moderate gain [3], or make use of Darlington configurations that offer higher effective [4], [5] for increasing the bandwidth, however, at the expense of integrating higher amount of noise.