Capacitor Discharging Through Asynchronous Circuit Switching

Operation elasticity due to the proportional relationship between energy and switching activity of asynchronous circuits has made them hugely attractive for energy harvesting systems. Using asynchronous logic makes it possible to minimize the power regulation efforts and instead, supply the circuit directly from the energy storage while a proper load scheduler is employed. In this context, the switching behaviour of the asynchronous load while it is powered by a capacitor becomes crucial to the effectiveness of the scheduler. This paper examines the relationship between the switching behaviour of a self-timed digital circuit and the dynamic characteristic of the voltage on the capacitor while the circuit is powered by the capacitor. For this purpose, a sample system is considered that consists of an initially charged capacitor which is discharged through the switching of a ring oscillator. Closed-form expressions are obtained for the supply voltage of the ring oscillator over time as it operates. Our analytical solution shows maximum 4.6% and 5.4% difference from experimental results in super and sub-threshold regions respectively. The experimental results are captured from a chip fabricated at 180nm technology node.