Digital signal processing for an adaptive phase-locked loop controller

Many piezoelectric systems are operated in resonance, requiring some sort of control. Especially weakly damped systems need a control algorithm to hold the system in resonance. There are many factors, which can change the system's resonant frequency during operation. The two most important factors are load effects and temperature effects. A common algorithm to drive a piezoelectric system in its eigenfrequency is the PLL (phase-locked-loop) controller - well known from communication technologies - including some adaptive variantions of the PLL. Beside a brief introduction into the APLL (adaptive PLL, this paper concentrates on one of the main components of the (A)PLL, the phase detector. It investigates and compares different types of phase detectors with a focus on the implantation on a digital control system.