On-Chip Self-Sensing Piezoelectric Micro-Lens Actuator With Feedback Control

High-speed micro-lens actuators are required for fast auto-focusing in miniaturized cameras. The speed can be enhanced by adding damping at the resonance frequency through feedback control. Previous approaches to implement the feedback control were based on expensive OFF-chip bulky laser sensors that are not suitable for miniaturized cameras. In this article, using an ON-chip self-sensing piezoelectric sensor with a novel readout circuit, a passive resonant controller (PRC) is designed, implemented, and tested. The stability of the closed-loop micro-lens actuator is guaranteed through the use of mixed negative-imaginary (NI) and passivity theory in the controller design. The performance of the controller with the ON-chip self-sensing piezoelectric sensor and readout circuit is compared to that OFF-chip laser sensor, and results show comparable performance. The closed-loop micro-lens actuator with the ON-chip piezoelectric sensor damps the fundamental resonance mode by 20.6 dB, which is similar to the 21.9 dB reduction obtained using the OFF-chip laser sensor. The settling time for the closed-loop actuator using the ON-chip self-sensing piezoelectric sensor is less than 10 ms, which is also comparable to the 8 ms obtained with the OFF-chip laser sensor. The signal-to-noise ratios (SNRs) for the ON-chip self-sensing piezoelectric sensor and OFF-chip laser sensor are 108 and 118 dB, respectively. These results show that the piezoelectric micro-lens actuator using the ON-chip self-sensing piezoelectric sensor can replace the bulky and expensive OFF-chip laser sensor without sacrificing performance, making it more appealing for portable micro-optics devices.