Substrate noise influence on circuit performance in variable threshold-voltage scheme

This paper investigates substrate noise influence on circuit performance in a variable threshold-voltage scheme (VT scheme) where threshold voltage is dynamically varied by substrate-bias control to reduce active power dissipation. It is experimentally examined that substrate-bias can be controlled stably with very few substrate-contacts. Measured tracking jitter of a delay-locked loop implemented by interconnections in an 8mm-square gate array does not degrade even when substrate-contacts are removed except for one at every strip of p-sub and n-well. A 2mm-square discrete cosine transform core processor with no substrate-contact except in its periphery operates at supply voltages from 1.3V to above 3V even though it employs small-swing differential dynamic pass-transistor logic. No performance degradation nor latchup is observed in these chips even when 100kΩ resistance is added to the substrate. These experimental results demonstrate noise immunity of the VT scheme, and indicate the possibility that the VT scheme can be applied to existing macro design easily.