Delta-Sigma Control of Dielectric Charge for Contactless Capacitive MEMS

A Second-Order Delta-Sigma Control of Dielectric Charge for Contactless Capacitive MEMS

“…The control method proposed in [7] addresses the above issues for devices working below pull-in. A "quasi-differential" device capacitance ∆C provides an indirect measurement of V sh , thus of Q d , at each sampling time.…”

“…One is the presence of tones in the spectrum of the bitstream (see fig. 18 in [7]), which poses a problem for retrieving real-time information about the charge…”

Simultaneous Control of Dielectric Charge and Device Capacitance in Electrostatic MEMS

“…The time parameters of BIT0 and BIT1 used are δ = 1/5 and T s = 1.2 s. For the first 6 hours, the device was actuated with an open loop sequence of alternating BIT0 and BIT1 symbols, with V + = −V − = 6 V. It is clearly observed that neither the device capacitance nor the net dielectric charge are controlled, since the C-V suffers from both horizontal and vertical displacements that are not being compensated. In the second stage, from t=6h to t=12h, the charge control method reported in [3] is used to set zero net dielectric charge (V sh th = 0 V). Fig.…”

“…Capacitance measurements performed at symbol times (1 − δ)T S and T S allow to obtain the quasi-differential capacitance ∆C = C + − C − , where C + and C − are the device capacitances measured when applying V + and V − , respectively. Taking into account that for voltages below pull-in the C-V can be approximated by a parabolic function [3], [9], V sh can be obtained at t = nT S as:…”

“…Although these techniques have demonstrated to increase the lifetime of devices, they cannot adapt to changes in the charge dynamics and therefore they may be not effective at long term. Regarding this, closed-loop charge control strategies based on sigma-delta modulation have been proposed [3], [4]. These controls periodically monitor the horizontal shift of the C-V, thus the net dielectric charge, by performing quasi-differential capacitance measurements and actuating the device with bipolar voltage waveforms, allowing to set the net dielectric charge to a target value.…”