Ultra low voltage supervisor for energy scavenging systems

In this paper, a voltage supervisor (VS) for low-voltage low-power energy harvesting systems (EHSs) is presented. The task of a VS is to change the logic state of its output when a conveniently scaled fraction of its supply voltage crosses a fixed threshold. The presented VS includes an ultra-low-voltage ultra-low-power reference, a voltage comparator, and an output latch. The circuit was specifically designed for energy scavenging applications that make use of a low-voltage source with a very limited current capability. Correct operation of the VS is ensured with a supply voltage as low as 300 mV. Current consumption is lower than 1 μA. An EHS was built to test the VS. The energy provided by the low-voltage harvester is first stored in a buffer capacitor, CIN; then, when the voltage across CIN reaches a predetermined voltage level, the VS enables a step-up circuit, which transfers the charge from CIN to an output capacitor at a higher voltage. Experimental results from a prototype are provided and discussed.