High-bandwidth and low-energy on-chip signaling with adaptive pre-emphasis in 90nm CMOS

Abstract

Long on-chip wires pose well-known latency, bandwidth, and energy challenges to the designers of high-performance VLSI systems. Repeaters effectively mitigate wire RC effects but do little to improve their energy costs. Moreover, proliferating repeater farms add significant complexity to full-chip integration, motivating circuits to improve wire performance and energy while reducing the number of repeaters. Such methods include capacitive-mode signaling, which combines a capacitive driver with a capacitive load [1,2]; and current-mode signaling, which pairs a resistive driver with a resistive load [3,4]. While both can significantly improve wire performance, capacitive drivers offer added benefits of reduced voltage swing on the wire and intrinsic driver pre-emphasis. As wires scale, slow slew rates on highly resistive interconnects will still limit wire performance due to inter-symbol interference (ISI) [5]. Further improvements can come from equalization circuits on receivers [2] and transmitters [4] that trade off power for bandwidth. In this paper, we extend these ideas to a capacitively driven pulse-mode wire using a transmit-side adaptive FIR filter and a clockless receiver, and show bandwidth densities of 2.2–4.4 Gb/s/µm over 90nm 5mm links, with corresponding energies of 0.24–0.34 pJ/bit on random data.