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.
Infrared thermal imager is widely used as target detection, search and tracking system due to its super night vision capability. The traditional thermal imager will cause column noise and serious image degradation due to temperature change, which will affect the observation effect. Therefore, it is necessary to carry out non-uniformity correction by the baffle (or shutter). However, in the process of shutter correction, there will be a short time for the search and tracking equipment to fail to work, which is easy to cause target loss. At present, all search and tracking systems require the installation of a continuously working infrared thermal imager without shutter. In order to realize the non-uniformity correction technology of infrared thermal imaging without shutter, a fast correction method for image gradient optimization based on noise template is proposed in this paper. Due to the special manufacturing process of the detector, when the temperature of the detector changes, the output image will produce vertical stripes with regular shapes. The noise patterns obtained at different temperatures are linearly related. Therefore, there is a noise model M, which makes the noise matrix at any temperature can be expressed as the product of M and a constant k (k is related to the detector Temperature K). The fringe noise of the image is quantified by detecting the sum of the absolute values of the transverse gradients of the image, and the non-uniformity correction without shutter is realized by adjusting the parameters so that the sum of the absolute values of the transverse gradients is minimized. This method can not only compensate temperature drift, but also replace the shutter to realize one-point correction, which reduces the power consumption of the whole machine and improves the reliability. There is no need for complicated calibration work in High and low temperature test chamber. It is not even necessary to record the current detector working temperature in real time for calculation. This method is simple in structure and easy to implement. The practical application proves that the infrared thermal imaging system has clear imaging. The effect is excellent.
At present, the resolution of cooled type infrared thermal imaging systems is generally low. In order to realize longdistance target detection, it is necessary to design a high-performance and high resolution infrared thermal imaging system. The methods of improving resolution both domestic and overseas are discussed and compared. A method of fast imaging in four quadrants by using a micro-scanner to drive an optical lens is proposed. The method has high control precision, simple process and easy realization. Four low-resolution images are spliced into one high-resolution infrared thermograph with high imaging quality. The infrared thermal imaging system designed by this method can search, locate and track targets tens of kilometers away with outstanding indexes and excellent performance.
Infrared thermal imager has developed rapidly in the field of military and civilian applications. How to objectively evaluate the imaging effect of the infrared thermal imager has become a problem that must be solved. Which not only provides quantitative mathematical description for the imaging performance of the infrared thermal imager, but also provides the supporting basis for the study of the image sharpness, target detection distance and target tracking performance of the infrared imaging system. The imaging evaluation system of thermal infrared imager proposed in this paper has the functions of infrared image data acquisition and processing. It is used to test and evaluate infrared image data in coordination with the target system of infrared imaging evaluation (composed of blackbody, radiation target console, collimating optical system and digital display precision turntable). The system has designed the main performance indexes, mathematical model and steps of image evaluation, including image non-uniformity, Signal Transfer Function (SiTF), Noise Equivalent Temperature Difference (NETD) three indicators to evaluate the noise and response characteristics of infrared thermal imager, and Angular Linearity, Target Imaging Positioning Angle Error two indicators to evaluate the image resolution characteristics of infrared thermal imager. After system testing, the performance is very superior and it becomes the necessary debugging and testing equipment in the development of infrared thermal imager.