Several approaches to post-silicon adaptation require feedback from a replica of the nominal critical path, whose variations are intended to reflect those of the entire circuit after manufacturing. For realistic circuits, where the number of critical paths can be large, the notion of using a single critical path is too simplistic. This paper overcomes this problem by introducing the idea of synthesizing a representative critical path (RCP), which captures these complexities of the variations. We first prove that the requirement on the RCP is that it should be highly correlated with the circuit delay. Next, we present two novel algorithms to automatically build the RCP. Our experimental results demonstrate that over a number of samples of manufactured circuits, the delay of the RCP captures the worst case delay of the manufactured circuit. The average prediction error of all circuits is shown to be below 2.8% for both approaches. For both our approach and the critical path replica method, it is essential to guard-band the prediction to ensure pessimism: our approach requires a guard band 30% smaller than for the critical path replica method.

Abstract-In nanoscale technologies that experience large levels of process variation, post-silicon adaptation is an important step in circuit design. These adaptation techniques are often based on measurements on a replica of the nominal critical path, whose variations are intended to reflect those of the entire circuit after manufacturing. For realistic circuits, where the number of critical paths can be large, the notion of using a single critical path is too simplistic. This paper overcomes this problem by introducing the idea of synthesizing a representative critical path (RCP), which captures these complexities of the variations. We first prove that the requirement on the RCP is that it should be highly correlated with the circuit delay. Next, we present three novel algorithms to automatically build the RCP. Our experimental results demonstrate that over a number of samples of manufactured circuits, the delay of the RCP captures the worst case delay of the manufactured circuit. The average prediction error of all circuits is shown to be below 2.8% for all three approaches. For both our approach and the critical path replica method, it is essential to guard-band the prediction to ensure pessimism: on average our approach requires a guard band 31% smaller than for the critical path replica method.

Due to increased variability trends in nanoscale integrated circuits, statistical circuit analysis has become essential. We present a novel method for post-silicon analysis that gathers data from a small number of on-chip test structures, and combines this information with pre-silicon statistical timing analysis to obtain narrow, die-specific, timing PDFs. Experimental results show that for the benchmark suite being considered, taking all parameter variations into consideration, our approach can get a PDF with the standard deviation 83.5% smaller on average than the SSTA result. The approach is scalable to smaller test structure overheads.

Due to increased variability trends in nanoscale integrated circuits, statistical circuit analysis has become essential. We present a novel method for post-silicon analysis that gathers data from a small number of on-chip test structures, and combines this information with pre-silicon statistical timing analysis to obtain narrow, die-specific, timing PDFs. Experimental results show that for the benchmark suite being considered, taking all parameter variations into consideration, our approach can get a PDF with the standard deviation 83.5% smaller on average than the SSTA result. The approach is scalable to smaller test structure overheads.

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