Statistical mixed Vt allocation of body-biased circuits for reduced leakage variation

Leakage current is susceptible to variation of transistor parameters and environment such as temperature, which results in wide spread in leakage distribution. The spread can be reduced by employing body biasing: reverse body bias for too leaky dies and forward body bias for too slow dies. We investigate body biasing of mixed V_t circuits. It is shown that the conventional body biasing has limitation in reducing leakage variation of mixed V_t circuits. This is because low- and high-l/t devices do not track each other and their body biasing sensitivities are different. We present alternative body biasing scheme that targets compensating die-to-die variation of low V_t. Under this body biasing scheme, within-die profiles of low- and high-l/t, which we need for statistical allocation of mixed V_t, get wider thus become different from the original ones. We present an analytical procedure to derive new within-die profiles. Experiments with 45-nm predictive model show that the spread in leakage distribution (ratio of maximum and minimum leakage) can be reduced to 4.5 as opposed to 9.4 from conventional body biasing on mixed V_t circuits.