A New CMOS Current-Mode Multiplexer for l0 Gbps Serial Links

Abstract

This paper presents an in-depth study of the pros and cons of voltage-mode multiplexers for Gbps serial links and exploits the advantages of multiplexing in current domain. In addition, it proposes a new fully differential CMOS current-mode multiplexer where a high multiplexing speed is achieved by multiplexing at a low-impedance node. Multiplexing speed is further improved by inductive shunt peaking with active inductors. The differential configuration of the multiplexer minimizes the effect of common-mode disturbances, particularly those coupled from the power and ground rails. The flow of the output currents in the opposite directions minimizes the effect of electro-magnetic interference from channels, making the multiplexer particularly attractive for high-speed data transmission over long interconnects and printed-circuit-board (PCB) traces. The proposed multiplexer draws a constant current from the supply voltage, thereby minimizing both switching noise and noise injected to the substrate. A fully differential CMOS current-mode 8-to-l multiplexer has been implemented in TSMC's 1.8 V 0.18 ?m CMOS technology and analyzed using Spectre from Cadence Design Systems with BSIM3.3v device models. Simulation results demonstrate that the multiplexer offers sufficiently large eye-opening when multiplexed at 10 Gbps.