Miniaturization of bandwidth extension circuit for ESD I/O pad using bridged T-coil

In this paper, we propose a miniaturization of the T-coil-based bandwidth extension circuit of electrostatic discharge (ESD) protected input/output (I/O) pad. In order to reduce the circuit size, the bridged T-coil is placed under the pad with ESD diodes. It is designed to have a wideband insertion and return losses and an improved eye opening, compared with the basic ESD I/O pad. The designed bandwidth extension circuit is verified by the electromagnetic simulations. The simulation shows that the designed I/O pad in a 28 nm FDSOI CMOS process exhibits a 3-dB bandwidth of 49.1 GHz, while meeting the OIF-CEI 56G mask limit for return loss. Additionally, the simulated eye diagram performance such as height, width, rise/fall time, and jitter are significantly improved, compared to the basic ESD I/O pad without T-coil.