Abstract
In this paper, a metastability immune warning flip-flop (FF) is proposed, which consists of an edge detector, a warning window generator, and a warning detector along with a traditional FF. The delayed data are monitored during the warning window to flag a warning signal before the data enter the erroneous zone. In this scheme, the warning window is independent of input clock frequency and hence is suitable for frequency scaling application. A 16-bit Kogge-stone adder is implemented in 65-nm technology, which uses warning FF for dynamic voltage and frequency scaling (DVFS). The warning FF-based DVFS allows elimination of safety margins and operates till the point of first warning of the adder without any erroneous results. The experiments were conducted with different supply voltages, phase-shifted clocks, and process conditions. The circuit is helpful to determine when to stop further reduction in supply voltage by producing the warning signal with predefined timing slacks in DVFS application. The test chip results demonstrate that the proposed circuit can track the critical path delay of 2.4-7.5 ns at warning voltage of 1.15-0.72 V, respectively. The measured results from 10 different chips show the effectiveness of the proposed concept across process variation.
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