  This paper presents the analysis of an efficient alternative interface
circuit for MEMS electrostatic energy harvesters. It is entirely composed by
diodes and capacitors. Based on modeling and simulation, the anti-phase
gap-closing structure is investigated. We find that when configured as a
voltage multiplier, it can operate at very low acceleration amplitudes. In
addition, the allowed maximum voltage between electrodes is barely limited by
the pull-in effect. The parasitic capacitance of the harvester and non-ideal
characteristics of electronic components are taken into account. A lumped-model
of the harvesting system has been implemented in a circuit simulator.
Simulation results show that an output voltage of 22 V is obtained with 0.15 g
input acceleration. The minimum necessary ratio between the maximum and minimum
capacitances of the generators which allows operation of the circuit, can be
lower than 2. This overcomes a crucial obstacle in low-power energy harvesting
devices. A comparison between the voltage multiplier against other current
topologies is highlighted. An advantage of the former over the latter is to
generate much higher saturation voltage, while the minimum required initial
bias and the minimum capacitance ratio in both cases are in the similar levels.
