We present a 4-Gb/s I/O circuit that fits in 0.1-mm 2 of die area, dissipates 90 mW of power, and operates over 1 m of 7-mil 0.5-oz PCB trace in a 0.25-m CMOS technology. Swing reduction is used in an input-multiplexed transmitter to provide most of the speed advantage of an output-multiplexed architecture with significantly lower power and area. A delay-locked loop (DLL) using a supply-regulated inverter delay line gives very low jitter at a fraction of the power of a source-coupled delay line-based DLL. Receiver capacitive offset trimming decreases the minimum resolvable swing to 8 mV, greatly reducing the transmission energy without affecting the performance of the receive amplifier. These circuit techniques enable a high level of I/O integration to relieve the pin bandwidth bottleneck of modern VLSI chips.

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