VaROT: Methodology for Variation-Tolerant DSP Hardware Design Using Post-Silicon Truncation of Operand Width

With increasing parameter variations in nanoscale technologies, computational blocks in Digital Signal Processing (DSP) hardware become increasingly vulnerable to variation-induced delay failures. These failures can significantly affect the Quality of Service (QoS) for a DSP chip leading to degradation in parametric yield. Existing post-silicon calibration and repair approaches, which rely on adaptation of circuit operating parameters such as voltage, frequency or body bias, typically incur large delay or power overhead in order to maintain QoS. In this paper, we present a novel low overhead approach of healing DSP chips by commensurately truncating the operand width based on its process corner. The proposed approach exploits the fact that critical timing paths in DSP data paths typically originate from the least significant bits (LSBs). This condition can also be satisfied by skewing the path delay distribution during logic synthesis or gate sizing. Hence, truncation of the LSBs, realized by setting them at constant values, can effectively reduce the delay of a unit, thereby avoiding delay failures. We also note that truncation of LSBs typically has minimal impact on QoS. Besides, efficient choice of truncation bits and values can minimize the impact on QoS. We propose appropriate design time modifications including insertion of low-overhead truncation circuit and gate sizing to maximize the delay improvement with truncation. Simulation results for a Discrete Cosine Transform (DCT) application at 45nm technology show large improvement in yield (41.6%) with up to 5X savings in power compared to existing healing approaches.