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基于FPGA和单片机的多功能等精度频率计设计

摘 要

基于传统测频原理的频率计的测量精度将随着被测信号频率的下降而降低，在实用中有很大的局限性，而等精度频率计不但有较高的测量精度，而且在整个测频区域内保持恒定的测试精度。运用等精度测量原理，结合单片机技术设计了一种数字频率计，由于采用了屏蔽驱动电路及数字均值滤波等技术措施，因而能在较宽定的频率范围和幅度范围内对频率，周期，脉宽，占空比等参数进行测量，并可通过调整闸门时间预置测量精度。选取的这种综合测量法作为数字频率计的测量算法，提出了基于FPGA 的数字频率计的设计方案。给出了该设计方案的实际测量效果，证明该设计方案切实可行，能达到较高的频率测量精度。

关键词 等精度测量，单片机，频率计，闸门时间，FPGA

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ABSTRACT

Along with is measured based on the traditional frequency measurement principle frequency meter measuring accuracy the signalling frequency the drop but to reduce, in is practical has the very big limitation, but and so on the precision frequency meter not only has teaches the high measuring accuracy, moreover maintains the constant test precision in the entire frequency measurement region. Using and so on the precision survey principle, unified the monolithic integrated circuit technical design one kind of numeral frequency meter, because has used the shield actuation electric circuit and technical measure and so on digital average value filter, thus could in compared in the frequency range and the scope scope which the width decided to the frequency, the cycle, the pulse width, occupied parameter and so on spatial ratio carries on the survey, and might through the adjustment strobe time initialization measuring accuracy. Selection this kind of synthesis measured the mensuration took the digital frequency meter the survey algorithm, proposed based on the FPGA digital frequency meter design proposal. Has produced this design proposal actual survey effect, proved this design proposal is practical and feasible, can achieve the high frequency measurement precision

Keywords Precision survey, microcontroller, frequency meter, strobe time，field programmable gate array

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1 绪论

测量频率是电子测量技术中最常见的测量之一。不少物理量的测量, 如时间、速度等都涉及到或本身可转化为频率的测量。目前, 市场上有各种多功能、高精度、高频率的数字频率计, 但价格不菲。而在实际工程中, 并不是对所有信号的频率测量都要求达到非常高的精度。

目前, 有三种常用的数字频率的测量方法: 直接测量法(以下称M法) 、周期测量法(以下称T法) 和综合测量法(以下称M /T法) 。M法是在给定的闸门时间内测量被测信号的脉冲个数, 进行换算得出被测信号的频率。T法是通过测量被测信号一个周期时间计时信号的脉冲个数, 然后换算出被测信号的频率。这两种测量法的精度都与被测信号有关, 因而它们属于非等精度测量法。而M /T法它通过测量被测信号数个周期的时间, 然后换算得出被测信号的频率, 克服了测量精度对被测信号的依赖性。M /T法的核心思想是通过闸门信号与被测信号同步, 将闸门时间τ控制为被测信号周期长度的整数倍。测量时, 先打开预置闸门, 当检测到被测信号脉冲沿到达时, 标准信号时钟开始计数。预置闸门关闭时, 标准信号并不立即停止计数, 而是等检测到被测信号脉冲沿到达时才停止, 完成被测信号整数周期的测量。测量的实际闸门时间与预置闸门时间可能不完全相同, 但最大差值不超过被测信号的一个周期。

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