Study Of Phase Distance Measurement Based On Dual-frequency Modulated Signals

As a way of positioning and reckoning, distance measurement has been applied inelectricity, aviation, military and other fields. Advances in science and technology at homeand abroad, which has promoted the rapid development of information industry and integratedcircuits, therefore gives people new understandings and requirements in various fields on therange, accuracy and speed of distance ranging system. The advantages and disadvantages arediscussed based on the analysis and comparison of various methods of distance measurement.Meanwhile considering demands for the project, the paper proposes a design of phasedistance measurement on dual-frequency modulated signals and discusses it in detail. Thedesign achieves high-precision positioning in some particular environment through the use oflow jitter, small frequency difference clock generation technology and phase-shiftmeasurement technology, etc.On the basis of resolving requirements of the task, the paper provides solutions andimplementations on short-range phase ranging study. From phase ranging principle, the paperdetails the overall design of the phase difference frequency laser ranging system and its keytechnology analysis, and makes special descriptions on both hardware circuits and softwarecontrol. The system mainly composes of cascaded PLL programmable modulation signalgenerating, laser transmission and receiving, signal processing, mixing and data acquisitionand digital phase detection. Sinusoidal wave modulation signals are obtained level of themeasuring tape with a slight frequency difference by programming low jitter clocks withdigital signal processor (DSP), and after filtered and mixed，they will be sent through anadjustable intensity laser emission; instead of the usual optical receiving system which detectsphase between transmitted signal and one single conditioning received signal, both of themare in nearly same condition which contains operational amplifying and gain adjustment to get two main frequency signals with phase information; after mixed with local oscillator signalsand passing through a narrowband frequency selective net whose voltage gain is greater thanone, the two high main signals are converted to IF signal; the DSP control part will getacquisition of these two channel analog signals and converts them to digital ones, so that theycan be in phase detective processing which can be used to obtain the distance to be measured.The paper proposes an overall design and circuit planning of phase method ranger finder,and debugging and performance testing of the front-end software and hardware are completed.The modulated signal source high frequency output (10MHz) phase noise offset at1kHz is-142dBc/Hz, and its RMS jitter is2.4ps, and it can also changes its signal original phase,which efficiently reduces noise and interrupting problems about the common DDS ones andmakes the best phase setting in signal processing become possible; dual optical conditioningcan be in automatic gain control (AGC), which holds an adjustable magnification of12to110and can be adapted to various types of optical receiving weak signal detection; the receivingsystem bandwidth is150MHz, ten times frequency difference dual modulation signals(reference1MHz) through the system owns stable phase difference; frequency-selective filternon-offset phase change turns out to be zero and it reduces the main phase impacting part insignal conditioning; Ranging error for one hundred meters on front-end circuits is6.657mm,thus the results verifies the system design’s rationality and basically meet the requirements ofthe subject.