Characterizing and Modeling Minimum Energy Operation for Subthreshold Circuits

Subthreshold operation is emerging as an energy-saving approach to many new applications. This paper examines energy minimization for circuits operating in the subthreshold region. We show the dependence of the optimum VDD for a given technology on design characteristics and operating conditions. Solving equations for total energy provides an analytical solution for the optimum VDD and VT to minimize energy for a given frequency in subthreshold operation. SPICE simulations of a 200K transistor FIR filter confirm the analytical solution and the dependence of the minimum energy operating point on important parameters.