The circuit in Fig. 1(a) is a sensor readout circuit developed by MEMS/NEMS research group

(simple but effective) at EE&T UNSW for amplifying a small charge (voltage) generated by

a PZT thin film in a micro-lens actuator when the actuator resonates. A PZT stands for lead

zirconium titanate. It is a piezoelectric material that transduces strain into an electrical charge

(voltage) and conversely applied voltage (charge) into strain. Hence, the material is used to

build actuators, which are devices that produce mechanical energy (force, moment and etc)

from electrical energy (applied voltage) - the most precise nanoscale movements in advanced

equipment, robotics, automobile, energy harvesters, and others are enabled by piezoelectric

actuators. The same material is also used to build sensors to detect tiny movements, pressure,

and forces such as touch screens, pressure sensors, accelerometers, gyroscopes and etc.

Fig. 1(b) shows the sensor readout circuit with the PZT actuator replaced by its electrical

equivalent circuit that consists of a voltage source (VPZT) in series with a capacitor (CPZT).

When the actuator is excited (driven) by Vin, it resonates and generates small VPZT. Hence,

VPZT is in phase with Vin