Zero-power wake-up sensing circuit in piezoelectric haptic feedback

Abstract

Piezoelectric elements are attractive for systems in which both sensing and actuating is required because a single element, i.e. the piezoelectric actuator, can be used that act as both a sensor and an actuator. In conventional systems combining both actuating and sensing functionality, active circuitry is required to read the sensor, and that circuitry requires static and/or dynamic current from a few microamps to a few milliamps. In systems where buttons are used a few times a day, this requirement for current leads to a significant amount of wasted power. Accordingly, a wake-up circuit is provided that does not draw power when no force is applied to the piezoelectric actuator but is capable of detecting pressure applied to the piezo actuator, generate a power-up signal to the actuating circuit, and initiate a haptic feedback with low-latency.