The Design Of AC Millivoltmeter Based On Random Equivalent Sampling

Digital AC millivoltmeter is an indispensable tool in electronic measuring and scientific experiments, it’s widely used in schools, factories and research institutes because of it’s features of high accuracy and easy reading. With the improvement of measurement requirements, higher bandwidth and higher precision is an important part of studying the AC millivoltmeter. The random equivalent sampling algorithm is used in the design of AC millivoltmeter, it not only improve the measure bandwidth as well as accuracy, but also reduce the requirement of analog to digital conversion rate.At present, most of the AC millivoltmeter on sale detects the signal amplitude by sophisticated detection method. However, the bandwidth of detection circuit is limited by the performance of detector diode, with the increase of signal frequency, measurement error will also increase. At the same time, a high flatness of analog channel is needed in this scheme, and this design becomes extremely difficult. This project entrusted by Jiangsu Lvyang Electronic Instrument Group Co., research and develop a digital AC millivoltmeter which have a wider frequency measurement range.It’s the key technical problem of developing AC millivoltmeter based on random equivalent sampling to achieve the algorithm of equivalent random sampling. In this paper, the author uses FPGA and MCU to implement the research of AC millivoltmeter based on random equivalent sampling, FPGA implements random equivalent sampling algorithms and peripheral logic module, in order to control the peripherals, MCU can transmit data to FPGA via the memory bus, and it also can obtain the sample data via this bus.The thesis analyzed two popular solutions:the solution of using random equivalent sampling and traditional detection circuit solution. It evaluates pros and cons of the two solutions. Besides, it introduces the design of relevant hardware and logic module in FPGA, especially the simulation of the key peripheral logic module. In addition, the thesis details the control software on MCU and configurate software for FPGA on PC as well as their working flow diagram. At last, the test of the whole system is given. The test indicates that the AC millivoltmeter has a equivalent sample rate up to 200MSa/s, analog bandwidth up to 20MHz, measurement error is less than 5% when frequency in 10Hz～10MHz and amplitude in 100μV-30OV, all of which meets the technical demands of the users.