ESSCIRC 2015

An Ultra-Low Power Capacitance Extrema and Ratio Detector for Electrostatic Energy Harvesters

Benjamin Saft¹, Eric Schäfer¹, Alexander Rolapp¹ and Eckhard Hennig²

¹IMMS GmbH, ²Reutlingen University

Session B3L-B: Energy Harvesting, September 16 2015, 13:20 – 15:20,

Abstract: The authors present a novel ultra-low power capacitance extrema and modulation ratio detector for electrostatic micro vibration energy harvesters. The circuit signals the points in time where a varying harvester capacitance Ch(t) reaches its minimum and maximum values Cmin and Cmax in each oscillation period. A novel feature is that the circuit allows the capacitance modulation ratio ac = Cmax/Cmin between two consecutive extrema to be determined digitally. The proposed circuit was implemented and fabricated in a commercial 0.35um CMOS process. Measurements were performed using a rotating capacitor with Cmax = 150 pF and adjustable ac spinning with up to 110 Hz. Transitions through capacitance extrema were measured for ac = 1.3...4.4 and were signalled accurately within the systematic time resolution limits of the method. In the presented configuration, the circuit draws a current of 60 nA from a 3.8-V supply.