MEDAC: A Metastability Condition Detection and Correction Technique for a Near-Threshold-V oltage Multi-V oltage-/Frequency-Domain Network-on-Chip

Abstract

This article presents a technique titled metastability condition detection and correction (MEDAC) that is featured in a near-threshold voltage (NTV) network-on-chip (NoC) hardware. The proposed technique introduces a double-sampling-based circuitry to detect whether the input data arrives too close to the receiver’s clock edge, which is defined as a metasta- bility condition. The MEDAC also contains a metastability condition mitigation scheme to monitor if the occurrence of such metastability conditions is frequent, and adaptively tune the receiver’s clock phase to increase the mean time between metastability conditions. We prototype a test chip of the NoC in a 65-nm low-power process, which supports four independent voltage/frequency (V/F) domains in globally asynchronous locally synchronous (GALS) systems. Measurements across 0.4–1-V sup- ply voltages with 13 different frequency ratios from 0.25 to 4 show that the MEDAC can well detect the metastability conditions and reduce the probability of entering such conditions by one to three orders of magnitude. This reduction, in turn, reduces the potential incorrect packets, thereby improving the data rate and energy efficiency by up to 21.1% and 27.2%, respectively.