数字频率的设计与制作

文档编号:DZXX166  文档字数:14734,页数:47

摘  要
传统数字频率计的测频误差主要包含两项σ=σ1+σ2。σ1为闸门时间的相对误差，在数值上等于频标信号的准确度，σ1=—ΔFs/Fs，Fs为频标信号频率；σ2位对测频技术的相对量化误差，σ2=±Tx/T，Tx为被测信号周期，T为闸门时间。σ1与所用石英晶体的频率稳定度有关，为减少σ1，常采用高稳定度的石英晶振；σ2是一变量，在同一闸门内低频段和高频段相差几个数量级，它对测频精度的影响最为严重。为减小σ2常采用下列方法：频率较低时改用测周期；多周期测量法；模拟内插法；频率倍增法等。采用这些方法对测频误差有一定的改善，但并未解决根本问题，且增加了软硬件成本。
本文介绍一种利用单片机实现的高精度测频仪，其特点是：
(1) 测量精度高，且在同一闸门内，各被测频率的测量精度相等，当闸门的时间为10s时，σ2≈10﹣7；
(2) 闸门时间在0.01s--10s间任意设置；
(3) 测频范围宽，Fx=0.1Hz—100M Hz；
(4) 预算速度高，通过特殊的定点数运算代替浮点数运算，运算中保留4字节有效数字；
(5) 显示软件中通过浮动小数点的位置显示8位十进制有效数字；
(6) 具有连续显示功能。
关键词：频率计、等精度测量、单片机

Abstract
For the traditional numeral frequency meter the frequency measurement error mainly contains two itemsσ=σ1+σ2. σ1 is the relative error of strobe time which in value is equal to the accuracy of standard frequency signal, σ1=-ΔFs/Fs, Fs is the standard frequency of the standard signal; σ2 is the relative quantification error to the frequency measurement technology, σ2=±Tx/T, Tx is the period of the measured signal, T is the strobe time. σ1 is related with the uses the frequency stability of the quartz crystal. σ1 often can be reduced by using high stability quartz crystal oscillator; σ2 is a variable, the value of which the differs several magnitudes between the low frequency band and the high frequency band in the identical strobe, so the influence to the frequency measurement precision of σ2 is the most serious. In order to reduceσ2 the following method is often used: chang to cycle measure when the frequency is low; multi-cycles measure; Analog interpolation; ampify the frequency and so on. By using these methods the frequency measurement error can be reduced for a little, but the basic problem can not be solved, and also increased the software and hardware cost.
In this article, we introduced a cymometer with high accuracy which realizes by using the monolithic integrated circuit, its characteristics are:
High Measuring accuracy, and the precision of all of the measured frequency is equal in the identical strobe, when the strobe time is 10s, σ2≈10 -7;
(2) The strobe time can be random setting in the rang of 0.01s--10s;
(3) The frequency measurement scope is wide, Fx=0.1Hz --100M Hz;
(4) The operation rate is high. By using special given points operation to replace the floating number operation, 4 byte significant digit is retains in the operation;
(5) In the software for display 8-bit decimal bases significant digits are displayed through the fluctuation decimal point position;
(7) It has the continuously demonstration function.
Key words:  Cymometer,  Measurements with the same precision,  Single-chip Machine

目  录

摘  要 I
Abstract II
第一章  引  言 1
1.1 国内外研制状况 1
1.2 课题的目的意义 1
1.3 预期达到的目标 2
1.4 设计所需要的仪器设备、器件 3
第二章 设计方案提出与论证 4
第三章  系统硬件设计 6
3.1 系统硬件总述 6
3.2 复位电路 6
3.3 时钟电路 8
3.4 分频电路 9
3.5  8051经8255与键盘显示器接口电路 11
3.5.1 键盘工作原理 11
3.5.2 LED显示器工作原理 12
3.5.3 其它主要功能器件 16
3.5.3.1 驱动LED显示器集成芯片7407 16
3.5.3.2  8051单片机芯片 17
3.5.3.3  8255微机并行接口芯片 18
3.5.4 键盘显示器接口整体电路图 20
3.6 整形放大电路 20
3.7 看门狗电路 22
第四章  系统软件系统设计 24
4.1 软件系统总述 24
4.2 系统初始化设计 24
4.3 键盘程序设计 24
4.4 测试程序设计 25
4.4.1 T0和T1工作方式确定 25
4.4.2 测试程序 26
4.5 数据处理程序设计 27
4.6本章小结 29
第五章  结论 30
致谢 31
附录1：数据处理程序 33
附录2：键输入原程序 41
附录3：显示程序 43
附录4：系统总硬件图 44

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