Design and research of phase-locked loop for infrared laser ranging system

Phase-locked loop (PLL) is a circuit that can synchronize the output signal with the input signal in frequency and phase. Generally, it consists of three parts: Phase Detector (PD), Loop Filter (LF) and Voltage Controlled Oscillator (VCO). In modern technology, it is widely used in various fields, such as modulation and demodulation, frequency synthesis, power system, laser ranging, image processing and so on. According to the number of zero and pole in open loop transfer function, PLL can be divided into two types: TYPE I and TYPE II (Charge Pump). In TYPE I PLL, there is only one zero and pole produced by VCO. Therefore, when the loop is locked, there is always a phase error between input and output. However, in TYPE II phase-locked loop, not only does it contain a zero and a pole generated by VCO, but it also introduces a charge pump into the phase-locked loop and provides another pole for the whole loop together with a phase detector, thus making the phase error zero when the loop is locked. Charge Pump Phase-Locked Loop (CPPLL) has a large phase-locked range. Charge pump phase-locked loop (CPPLL) is widely used because of its large capture range and relatively simple structure. In this paper, the principle of charge pump phase locked loop (CPPLL) in phase laser ranging is analyzed, the linear model is built, and the performance of speed conversion is studied. The frequency-locked, phase-locked precision and conversion speed of the loop are analyzed, and the charge pump phase-locked loop circuit is designed. Experiments show that the circuit effectively prevents the charge sharing effect and improves the accuracy and speed of the system.