Research And Realization Of High-precision Dual-channel Frequency Measurement System

Frequency is one of the most basic parameters in electronic technology.Because of its strong anti-interference ability,rich information carrying,and easy long-distance transmission,it is often widely used in aerospace,satellite navigation,communications,geological exploration and other fields to transmit important information.In addition,the frequency measurement method is simple,can be used to achieve high measurement accuracy,and is closely related to many electrical parameter measurement schemes and measurement results.Therefore,high-precision frequency measurement is particularly important for the entire field of electronic measurement.In this thesis,design ideas provided by many companies at home and abroad using on their frequency measurement products already was discussed.And after analyzing a variety of frequency measurement methods,a combination scheme of phase detection broadband frequency measurement technology and equal-precision frequency measurement is proposed.Then using FPGA+CPCI structure as the bus interface,a multi-functional high-precision dual-channel frequency measurement system was designed and implemented.In this thesis,the application background of high-resolution frequency measurement systems and the development status of modern frequency measurement systems are firstly explained.Secondly,combined with the design scheme of common general counters,a variety of frequency measurement methods are introduced,and their respective advantages and disadvantages are analyzed.In order to eliminate the±1 count error existing in the traditional frequency measurement method,as well as broaden the frequency measurement range and improve the measurement accuracy,a scheme using phase detection broadband frequency measurement technology combined with equal-precision frequency measurement is proposed.Then,according to the system requirements,a signal conditioning circuit with wide dynamic range,high signal-to-noise ratio,and programmable control was designed and implemented to improve the flexibility of measurement;and a high-speed comparator circuit with adjustable trigger level and hysteresis voltage was designed to make the anti-interference ability of the circuit is enhanced.The design of the measurement logic of each parameter(frequency,period,time interval,frequency ratio,etc.),the configuration of the programmable analog signal input channel,and the design of the CPCI interface and the communication logic of the host computer were programmed inside the FPGA.Compared with the traditional design,it not only improves the operating speed of the system,but also greatly enhances the stability and integration of the entire system.At last,actual functional testing of the system was performed with signal generators,oscilloscopes,CPCI chassis,host computer and other equipment.The test proves that under the crystal oscillator of 4.05×10^-8's frequency accuracy and 1 second gate time,the relative error of the designed system for frequency measurement is better than 5×10^-7.The measurement indicators meet the design requirements,which verified the correctness and practicability of the entire design.