Metastability challenges for 65nm and beyond; simulation and measurements

Recent synchronizer metastability measurements indicate degradation of MTBF with technology scaling, calling for measurement and calibration circuits in 65nm and below. Degradation of parameters can be even worse if the system is operated at extreme supply voltages and temperature conditions. In this work we study the behavior of synchronizers in a broad range of supply voltage and temperature corners. A digital on-chip measurement system is presented that helps to characterize synchronizers in future technologies and a new calibrating system is shown that accounts for changes in delay values due to supply voltage and temperature changes. We present a detailed comparison of measurements and simulations for a fabricated 65nm bulk CMOS circuit and discuss implications of the measurements for synchronization systems in 65nm and beyond. We propose an adaptive self-calibrating synchronizer to account for supply voltage, temperature, global process variations and DVFS.