Built-in proactive tuning for circuit aging and process variation resilience
Shah, Nimay Shamik
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VLSI circuits in nanometer VLSI technology experience significant variations - intrinsic process variations and variations brought about by transistor degradation or aging. These are generally embodied by yield loss or performance degradation over operation time. Although the degradation can be compensated by the worst-case scenario based over-design approach, it induces remarkable power overhead which is undesirable in tightly power-constrained designs. Dynamic voltage scaling (DVS) is a more powerefficient approach. However, its coarse granularity implies difficulty in handling finegrained variations. These factors have contributed to the growing interest in poweraware robust circuit design. In this thesis, we propose a Built-In Proactive Tuning (BIPT) system, a lowpower typical case design methodology based on dynamic prediction and prevention of possible circuit timing errors. BIPT makes use of the canary circuit to predict the variation induced performance degradation. The approach presented allows each circuit block to autonomously tune its performance according to its own degree of variation. The tuning is conducted offline, either at power on or periodically. A test pattern generator is included to reduce the uncertainty of the aging prediction due to different input vectors. The BIPT system is validated through SPICE simulations on benchmark circuits with consideration of process variations and NBTI, a static stress based PMOS aging effect. The experimental results indicate that to achieve the same variation resilience, proposed BIPT system leads to 33% power savings in case of process variations as compared to the over-design approach. In the case of aging resilience, the approach proposed in this thesis leads to 40% less power than the approach of over-design while 30% less power as compared to DVS with NBTI effect modeling.