Driver ASIC for synchronized excitation of resonant micro-mirrors
We present an ASIC for synchronized excitation of electrostatically driven resonant micro scanning mirrors which have been developed and fabricated at the Fraunhofer IMS for several years. The mirror oscillation is excited with a rectangular driving signal and operated close to the characteristic frequency or higher. Deflection amplitude is maximum if the driving voltage is switched off precisely at the cross-over of the oscillation. We have developed and fabricated a mixed signal ASIC that starts the oscillation and runs the mirror with high efficiency by detecting the oscillation cross-over. For that, the ASIC senses the varying capacitance of the actuator's comb-drive electrodes and converts it with a clocked charge amplifier into a voltage. The amplified capacitance signal is processed by a synchronization module which detects the minimum of the capacitance signal corresponding to the cross-over of the oscillation. An integrated charge pump provides the driving voltage. The ASIC has been fabricated at the facilities of the IMS with a 1.2 µm CMOS process. Tests with a demonstrator PCB have shown that the synchronization works highly efficient with a value of appr. 96 %. A mechanical deflection angle of +/- 13° was achieved for a micro-mirror with a characteristic frequency of 250 Hz at a driving voltage of 13.5 V, only.