A 85mV 40nW Process-Tolerant Subthreshold 8×8 FIR Filter in 130nm Technology

Subthreshold operation is limited by low performance and high susceptibility to process variation. We propose variation tolerant ultra-dynamic voltage scaling (UDVS), and as an example we present an 8 times 8 process-tolerant FIR filter, working in both superthreshold and subthreshold regions featuring adaptive beta-ratio modulation and integrated level converters. Measurements show that the filter works at 85 mV consuming 40 nW, and the proposed method can salvage circuits which potentially failed to operate due to variations.