Interconnect Length Detection Based On FMCW

In the ranging system,frequency-modulated continuous wave(FMCW)technology has the characteristics of low transmission power and high resolution compared with the timeof-flight(To F)method and does not rely on high-precision timing system.Therefore,it is widely used in military high-precision radar ranging and automatic driving of civil vehicles(laser radar).In this thesis,combining the popular FMCW technology with electronic package assembly test,a PCB board-level interconnect line length detection system is designed and implemented.Firstly,FMCW-related technologies being investigated,mainly the generation mode and length detection principle.In understanding the basis of the principle of system,the system simulation and scheme demonstration of FMCW detection board-level interconnect are carried out by using Optisystem simulation software.Meanwhile,the parameters such as distributed inductance,distributed capacitance and distributed resistance on the interconnect are calculated by mathematical formula.Secondly,On the basis of understanding various FMCW waveform generation methods-VCO(voltage-controlled oscillator),PLL + ΔΣ modulation(phase locking loop)and DDS(direct digital synthesis),according to the design requirements,the AD9910 chip of ADI company was selected,developed the DDS frequency synthesizer with100MHz~200MHz bandwidth,and wrote the code control synthesizer to generate the FMCW triangle modulation wave.Thirdly,according to the principle of analog multiplier,the peripheral circuit of AD835 chip is configured,and a beat module based on AD835 multiplier is designed.The output of the beat frequency module is the " beat frequency" and " additional frequency " of the two input signals.In order to detect the beat frequency signal,so a Sallen-key active filter composed of multiple operational amplifiers is designed.The two modules are connected in turn to complete the reception and filtering of the test signal.Finally,On the basis of completing the hardware design,the experiment of interconnect length detection based on FMCW is designed.The relevant parameters of PCB interconnect length detection are determined,such as measurement accuracy of 2mm,frequency sweep period of 40 us,interconnect reference length,etc.The software code and hardware circuit are debugged cooperatively.Finally,the data of interconnect length detection experiment show that the maximum error is 2.73 mm,the minimum error is 1.05 mm,and The average absolute deviation is 1.64 mm.In summary,this dissertation takes the board-level interconnect detection as the object,uses DDS to generate frequency-modulated continuous wave,carries out the theoretical derivation,experimental simulation,circuit implementation and board-level interconnect test based on FMCW detection technology,and finally completes the length detection of PCB interconnect based on frequency-modulated continuous wave.