Dynamic measurement of critical-path timing

A high bandwidth critical path monitor (1 sample/cycle at 4-5 GHz) capable of providing real-time timing margin information to a variable voltage/frequency scaling control loop is described. The critical path monitor tracks the critical path delay to within 1 FO2 inverter delay with a standard deviation less than 3 FO2 delays over process, voltage, temperature, and workload. The CPM is sensitive to 20mV/bit A/C and 10mV/bit DC voltage changes, and less than 10°C/bit temperature changes.