Field profiling & monitoring of payload transistors in FPGAs

A new use for ring-oscillators (ROs) is proposed by which PMOS and NMOS transistor strengths can be measured and monitored in the field. A new metric, based on RO duty-cycle is defined. This new metric, along with RO-frequency, offers a way to profile and bin transistors based on their drive strengths. With ROs configured from payload transistors, along with the natural programmability of FPGAs, this strength based profiling can be done in the field at a level of granularity that is not possible with existing methodologies. New applications of the metrics and the profiling methodology include use of on-die ROs as a (a) monitor and control for duty-cycle sensitive designs, (b) replacement for scribe-line test structures, and (c) sensor for payload transistor characteristics over life-time.