Analysis of adaptive clocking technique for resonant supply voltage noise mitigation

Resonant supply voltage noise is emerging as a serious limitation for power efficiency in SoCs for mobile products. Increasing supply currents coupled with stagnant package inductance is leading to significant AC supply impedance, which necessitates increasing supply voltage margins, impacting power efficiency. Adaptive clocking offers a potentially promising approach to reduce voltage margins, by stretching the clock period to match datapath delays. However, the adaptation bandwidth and clock distribution latencies required can be very demanding. We present analysis of the potential benefits from adaptive clocking based on measurements of supply voltage noise in a dual-core ARM Cortex-A57 cluster in a mobile SoC. By modeling an adaptive clocking system on the measured supply voltage noise dataset, we demonstrate that an adaptation latency of 1.5ns may offer a VMIN improvement of around 30mV and at 1ns improvements of 50mV. Benefits are workload dependent and ultimately limited by insurmountable synchronization and clock distribution latency.