The continuous increase of leakage power consumption
in deep sub-micro technologies necessitates more aggressive
leakage control. Runtime leakage control (RTLC) is effective,
since runtime circuits generally have significant amount
of idleness. However, current RTLC techniques are only used
when circuits have long idleness, rendering the techniques
less profitable. The reason is due to the large energy and
delay overhead when performing RTLC mode transition. We
propose two novel techniques, workload-adaptive Vth hopping
(WAVTH) and hierarchical Vth hopping (HIVTH), to
tackle the overhead problems and enable aggressive runtime
leakage control. Experimental results show 19.2% average
improvement on leakage saving with WAVTH and HIVTH
over basic Vth hopping. The optimum design points of these
two techniques are determined through accurate modeling.