An integrated capacitive sensing method for electrostatic comb-drive micromirrors

In this work, a real-time capacitive sensing scheme based on electromechanical amplitude modulation is developed to detect the scanning angle and phase of a uniaxial electrostatic comb-drive micromirror for close loop control. In this scheme, a sine-wave voltage signal superimposed with a high frequency carrier signal is applied to the shared comb drives of the micromirror for both sensing and driving. The driving/sensing circuit is fully analyzed in both frequency and time domain for feedthrough elimination and signal distortion minimization. Experimental results have shown that using a carrier signal with 2.5 V_pp and 1 MHz, the measurement accuracy of the scanning angle of the micromirror reaches 0.15° and the time delay can be controlled within 0.47 μs. The effect of the temperature change on the phase response of the micromirror is also investigated for a better understanding of the micromirror's scanning stability. When the temperature changes from 25 °C to 35 °C, the measured time delay of the micromirror actuated at 3840 Hz changes from 0 to 2.4 μs. The proposed capacitive sensing scheme can be used to effectively measure the angular position and phase of electrostatic comb-drive MEMS mirrors simultaneously without the need of adding any external components.