Low-voltage CMOS current-mode preamplifier: analysis and design

This paper presents the analysis and design of a new low-voltage fully balanced differential CMOS current-mode preamplifier for multi-Gbps series data communications. The minimum supply voltage of the proposed preamplifier is V_T+V_sat. The preamplifier employs a balanced configuration to achieve large bandwidth and to minimize the effect of bias-dependent mismatches. Two new bandwidth enhancement techniques, namely inductive series peaking and current feedback that are specific to low-voltage CMOS current-mode circuits, are introduced. The inductive series peaking technique utilizes the resonant characteristics of LC networks to achieve both a flat frequency response and maximum bandwidth. Current feedback extends bandwidth, lowers input impedance, and improves dynamic range. The employment of both techniques further increases the bandwidth, reduces the value of the series peaking inductor, and improves noise performance of the pre-amplifier at high frequencies. The preamplifier has been designed using a 0.18-μm 6-metal 1-poly 1.8-V CMOS technology. Simulation results from Spectre with BSIM3.3 device models that account for device parasitics demonstrate that the preamplifier has a flat frequency response with 25.3 dB dc current gain or equivalently 60 dBΩ transimpedance gain with a 50-Ω load and bandwidth of 2.15 GHz.