Control system of all-digital phase-locked loop for phase-shift laser ranging

This paper introduces an FPGA-based all-digital phase-locked loop(ADPLL) control system for phase-shift laser ranging. The system can improve the accuracy of the phase frequency detector and is immune to the effects of temperature and voltage, thus significantly reducing the frequency error in phase detection of phase-shift laser ranging. It consists of a digital phase detector, a digital filter and a digitally controlled oscillator. When the reference signal generated inside the FPGA is 40 Hz, the sampling period is 0.025 s and the output reaches saturation (about 5 V) after approximately 300 ms. The ADPLL control system avoids the problems often encountered by analog circuits, like incomplete transmission, parasite, temperature fluctuations and aging. Moreover, it is easy to test and reset.