Synthesis and Analysis of Design-Dependent Ring Oscillator (DDRO) Performance Monitors

With CMOS technology scaling, circuit performance has become more sensitive to manufacturing and environmental variations. Hence, there is a need to measure or monitor circuit performance during manufacturing and at runtime. Since each circuit may have different sensitivities to process variations, previous works have focused on the synthesis of circuit performance monitors that are specific to a given design. We develop a systematic approach for the synthesis of multiple design-dependent monitors, as well as the corresponding calibration and delay estimation methods. Our approach synthesizes design-dependent ring oscillators (DDROs) using standard-cell library gates and conventional physical implementation flows. Our delay estimation method limits the memory usage overhead by clustering critical paths with similar delay sensitivities. Experimental results show that our delay estimation method using multiple DDROs reduces overestimation (timing margin) by up to 25% compared to using a single monitor. Furthermore, our silicon measurement results for monitoring an industrial microprocessor implemented in a 45-nm silicon-on-insulator process show that DDRO can reduce the mean delay estimation error by 35% compared to inverter-based ring oscillators.