光斑位置检测系统中数字锁相放大器的设计与实现

	光斑位置检测系统中数字锁相放大器的设计与实现
其他题名	Design and Implementation of Digital Lock-in Amplifier in theSpot Position Detection System
	张辉
学位类型	硕士
导师	陈涛
	2015-11
学位授予单位	中国科学院大学
学位专业	机械电子工程
关键词	光斑位置检测系统数字锁相放大器相关检测低噪放大器数据采集系统
摘要	近年来激光通信因其通信容量大、抗干扰能力强、结构轻便、设备经济等优点，获得了人们广泛的关注，已成为诸多学者研究的热点。光斑位置检测系统是激光通信中重要的组成部分，其检测精度将直接影响通信质量。作为光斑位置检测系统常用的反馈器件之一，四象限探测器(four-Quadrant Detector, QD) 转换的微弱光电流经放大后解算出光斑位置反馈给伺服系统完成精跟踪，由于背景光、电路噪声等因素的影响，光电转换后的微弱电流中主要包含低频噪声，这将极大的降低QD 最终的检测精度。此外由于QD 的工作频率也在低频段，采用传统的放大技术很难有效地抑制这些噪声。而锁相放大器通过频谱搬移将有用信号的频率从低频搬到高频，在抑制低频噪声方面有很大的优势，它能够测量到输入信噪比低达10-5 的微弱正弦量，具有很高的检测精度。随着数字技术的不断进步，锁相放大器也由模拟型向数字型发展,数字锁相放大器克服了模拟锁相放大器的温漂和其他非理想的低频特性，极大改善了锁相放大器的性能，使锁相放大器的研究发展和应用得到了很大提高。本文将数字锁相放大技术应用到光斑位置检测系统中，首先深入研究了光斑位置检测和锁相放大理论；然后在此基础上设计并实现了数字锁相放大系统，主要由低噪声、高增益前置放大器和高精度数据采集处理系统两部分组成；最后进行了系统测试，实验结果表明数字锁相放大器能够有效地抑制背景光噪声，改善系统信噪比，提高光斑位置检测精度，达到工程要求。具体研究内容包括： 1.研究了高斯光斑模型下位置检测的基本原理，推导出了位置检测精度的数学模型，研究结果表明影响QD 位置检测精度的因素主要有光斑半径、光斑质心位置和系统信噪比，其中最主要因素是系统信噪比，因此提出将数字锁相放大技术应用于光斑位置检测系统中。 2.研究了锁相放大器的检测原理，重点分析了相关检测技术和相关解调算法，并用Matlab/simulink 对单通道和双通道锁相放大器进行了建模仿真，为数字锁相放大系统设计提供了理论基础。 3.设计了低噪声、高增益前置放大器，将受调制的微弱光电流转换成电压，以利于AD 的采集。电路由跨阻放大电路、调零-电压调整电路和有源带通滤波电路三级组成，在其放大倍数为2.5×107V/A 时，开路噪声约为35uV，与理论计算值30uV 基本吻合。 4.设计了高精度数据采集和处理系统，当AD 模拟输入端短路时，系统的输出噪声为10～20uV，有效位数达到18～19 位。此外，在FPGA 中设计了AD 控制器、数字相关解调、参考信号发生器以及数字低通滤波器等模块，实现了信号解调功能。 5.搭建了光斑位置检测平台对数字锁相放大器进行了测试，并与传统的测试方法进行了对比，对比结果表明数字锁相放大器应用于光斑位置检测系统中是可以有效地抑制背景光噪声的，改善系统信噪比，提高光斑位置检测精度，其位置检测精度已优于1μm。
其他摘要	In recent years, the laser communication has taken widespread attention because of its advantages, such as large communication capacity, strong anti-interference ability, light structure, and economic equipment, etc., and has become a research hot spot for many scholars. Spot position detection system is an important part of laser communication, and its detection accuracy will directly affect the quality of communication. Four quadrant detector(QD) as one of the commonly used feedback components of the spot position detection system, the weak conversion photocurrent is amplified to calculate the position of facula, and then feedback to the servo system to complete the precision tracking. Due to the influence of background light and circuit noise, the weak current of the photoelectric conversion mainly contains low frequency noise, which will greatly reduce the detection accuracy of QD. In addition, the working frequency of QD is also in the low frequency band, it is difficult to effectively suppress the noise by the traditional amplification technology. The lock-in amplifier moves the frequency of useful signal from low to high by frequency spectrum shift, and it has great advantages in inhibition of low-frequency noise. It can measure weak sinusoidal signal with SNR as low as 10-5 and has very high accuracy. With the development of digital technology, the lock-in amplifier is developed from the analog to the digital type. The digital lock-in amplifier has overcome the temperature drift and other non-ideal low frequency characteristics, which greatly improve the performance of the lock-in amplifier, so that research development and application of lock-in amplifier has been greatly improved. In this paper, the digital lock-in amplifier is applied to the spot position detection system. Firstly, the theory of spot position detection and lock-in amplifier are studied; Secondly, the digital lock-in amplifier system is designed and implemented, which is composed of two parts: the low noise, high gain preamplifier; and high precision data acquiring, processing system; Finally, the system is tested. The experimental results show that the digital lock-in amplifier can effectively suppress the background light noise, improve the SNR of system and meet engineering requirements. The main research contents include: 1. The basic principle of position detection of Gauss spot model is studied, and the mathematical model of the position detection accuracy is derived. The research results show that the main factors affecting the accuracy of QD position detection are spot radius, centroid position and SNR of system. The most important factor is the SNR of system. Therefore, digital lock-in amplifier technology applied to light spot position detection system is proposed. 2. The detection principle of the lock-in amplifier is studied, the correlation detection technique and correlation demodulation algorithm are analyzed, the modeling and simulation of the single channel and dual channel lock-in amplifiers are carried out with Matlab/simulink. It provides a theoretical basis for the design of digital lock-in amplifier system. 3. A low noise, high gain preamplifier is designed, which converts the weak light current into voltage, for facilitating the acquisition of AD. The circuit is composed of three parts which are cross resistance amplifying circuit, zero - voltage adjustment circuit and active band pass filter. The open circuit noise is about 35uV when the amplification factor is 2.5×107V/A, and is consistent with the theoretical calculation value which is 30uV. 4. High precision data acquiring and processing system is designed. The output noise is 10～20uV when the input is short, and the effective number of AD can be up to 18～19 bits. In addition, the AD controller, digital correlation demodulation, reference signal generator and digital low pass filter are designed in FPGA. And signal demodulation function is realized. 5. The digital lock-in amplifier is tested by the spot position detection platform， and then compared with the traditional test method. The comparison results show that the digital lock-in amplifier can effectively suppress the background light noise, improve the SNR of system, and then improve accuracy of the spot detection. And the accuracy of the spot detection is higher than 1μm.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/49251
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	张辉. 光斑位置检测系统中数字锁相放大器的设计与实现[D]. 中国科学院大学,2015.

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