Design of a High-Speed and Low-Power Threshold Adjustment Unit for Battery-Free Edge Devices

It is an attractive feature to make the capacity of power storage as small as possible in battery-free devices, while it may cause task failure frequently because of its unsatisfactory amount of power storage. This paper describes the design of a power control circuit using a threshold adjustment unit (TAU), that can adjust the energy harvested by a battery-less device for different tasks. The scheme sets a properly sized capacitor as power storage, which can adjust its power capacity prepared for tasks with different power consumptions by changing the charging and discharge threshold, thus avoiding task failure caused by insufficient power supply. Meanwhile, the high-speed and low-power design of this scheme can reduce the overhead caused by judging the charging/ discharging voltage and the threshold voltage. By applying this unit to a battery-free configuration that assumes RF power feeding, charge and discharge path control at various thresholds in intermittent computing can be completed automatically and with low overhead. With the simulation of HSPICE based on 45nm CMOS, the average power consumption and response delay of the proposed trigger circuit with double-rail discrete-time comparator are only 45.9 mu W and 39.0 mu s, respectively.