The Research Of Three Channel High Precision I/F Converter

I/F converter, i.e. the current-frequency converter,is a device which convertsinput current signal to output frequency signal according to a linear proportionrelationship. The conversion accuracy of conventional I/F converter is only about afew thousandths, temperature drift up to several hundred ppm, this paper design aI/F converter which conversion accuracy is less than five hundred thousandths, itstemperature drift is controlled in less than10ppm, it is applied in military productswhich must have very high accuracy.This project is mainly to design a three-channel,high-precision digital I/F converter (hereinafter referred to as Digital I/F converter).According to the principle of the I/F converter and the features of the input signalsand output signals, this paper choose to use a high-performance24-bit A/Dconverter ADS1256produced by TI and a high-performance16-bit digital signalcontroller MC56F8037produced by Freescale to design a high-performance threechannel digital I/F converter which nonlinearity of output frequency precisionwithin5×10-5. In this paper, we designed the converter from the perspective of bothhardware and software to improve the accuracy and the robustness of the system.In this paper, we designed the corresponding signal conditioning circuits, A/Dsampling circuit and a digital frequency synthesizer circuit after deep analysis theoperating principle of the I/F converter. The I/F converter converted input currentinto corresponding output voltage firstly, then take sample of the voltage signal,after that,we designed a Digital filter to filter the sampled signal, supplemented bynon-linear variable gain compensation algorithm to improve the I/F converterconversion accuracy to solve the converter’s serious drift problems, finally, use thedigital frequency synthesis method to output each channel’s frequency, according tothe experimental measurement, the I/F converter can fully meet the systemrequirements.