Rapid FPGA delay characterization using clock synthesis and sparse sampling

Abstract

This paper introduces a set of novel techniques for rapid post-silicon characterization of FPGA timing variability. The existing built-in self-test (BIST) methods work by incrementing the clock frequency until timing failures occur within the combinational circuit-under-test (CUT). A standing challenge for industrial adoption of post-silicon device profiling by this method is the time required for the characterization process. To perform rapid and accurate delay characterization, we introduce a number of techniques to rapidly scan the CUTs while changing the clock frequency using off-chip and on-chip clock synthesis modules. We next find a compact parametric representation of the CUT timing failure probability. Using this representation, the minimum number of frequency samples is determined to accurately estimate the delay for each CUT within the 2D FPGA array. After that, we exploit the spatial correlation of the delays across the FPGA die to measure a small subset of CUT delays from an array of CUTs and recover the remaining entries with high accuracy. Our implementation and evaluations on Xilinx Virtex 5 FPGA demonstrate that the combination of the new techniques reduces the characterization timing overhead by at least three orders of magnitude while simultaneously reducing the required storage requirements.