武汉轻工大学
毕业设计外文参考文献译文本
2013届
原文出处：from Vin Skahill.VHDL for Programmable Logic
page 76-88
毕业设计题目：基于FPGA的数字频率计设计
院（系）：电气与电子工程学院 专业名称：电子信息科学与技术 学生姓名： 学生学号： 指导教师：
Introduction of digital frequency meter
Digital Frequency is an indispensable instrument of communications equipment, audio and video, and other areas of scientific research and production . In addition to the plastic part of the measured signal, and digital key for a part of the show, all the digital frequency using Verilog HDL designed and implemented achieve in an FPGA chip. The entire system is very lean, flexible and have a modification of the scene.
1 、And other precision measuring frequency Principle
Frequency measurement methods can be divided into two kinds:
(1) direct measurement method, that is, at a certain time measurement gate measured pulse signal number.
(2) indirect measurements, such as the cycle frequency measurement, VF conversion law. Frequency Measurement indirect measurement method applies only to low-frequency signals.
Based on the principles of traditional frequency measurement of the frequency of measurement accuracy will be measured with the decline in signal frequency decreases in the more practical limitations, such as the accuracy and frequency of measurement not only has high accuracy, but also in the whole frequency region to maintain constant test accuracy. The main method of measurement frequency measurement Preferences gated signal GATE issued by the MCU, GATE time width on the frequency measurement accuracy of less impact, in the larger context of choice, as long as the FPGA in 32 of 100 in the counter b M Signals are not overflow line, in accordance with the theoretical calculation GATE time can be greater than the width Tc 42.94 s, but due to the single-chip microcomputer data processing capacity constraints, the actual width of less time, generally in the range of between 0.1 s choice, that is, high-frequency, shorter gate;, low gate longer. This time gate width Tc based on the size of the measured frequency automatically adjust frequency measurement in order to achieve the automatic conversion range, and expanded the range of frequency measurement; realization of the entire scope of measurement accuracy, reduce the low-frequency measurement error.
The design of the main methods of measuring the frequency measurement and control block diagram as shown in Figure 1. Figure 1 Preferences gated signal GA TE issued by the MCU, GA TE time width of less frequency measurement accuracy, in the larger context of choice, as long as the FPGA in 32 of 100 in the counter b M
signal Overflow will do, according to theoretical calculations GA TE time width T c can be greater than 42194 s, but due to the single-chip microcomputer data processing capacity constraints, the actual width of less time, generally 10 to 011 s in the inter-choice, that is, high - band, the gate time shorter, low gate longer. This time gate width based on the measured T c automatically adjust the size of frequency measurement frequency range to achieve the automatic conversion, and expanded the range of frequency measurement; realization of the entire scope of measurement accuracy, reduce the low-frequency measurement error.
2、 Frequency of achieving
Frequency Measurement accuracy of such method. Can be simplified as shown in the diagram. Map CNT1 and CNT2 two controllable counter, standard frequency (f) signal from the CN F1 clock input cI K input, the signal measured after the plastic (f) CNT2 clock input cI K input. Each counter in the CEN input as enable end, used to control the counter count. When the gate signal is HIGH Preferences (Preferences start time). Signal measured by the rising edge of the D flip-flop input, launched at the same time with two counts of juice; Similarly, when preferences for low gate signal (the end of Preferences time), the rising edge of the measured signals through D Trigger output end of the counter to stop counting.
3、And the median frequency of relevant indicators
Median: At the same time the figures show that up to the median. The usual eight-count frequency of only several hundred yuan can buy. For high precision measurements, nine just beginning, the middle is 11, 13 can be relatively high.
Overflow of:-the ability to promote itself to overflow the equivalent of the total. Some of the frequency with overflow function, which is the highest overflow does not display only shows that the bit behind, in order to achieve the purpose of the median. Here is the estimated value of individual indicators.
Speed: namely, the number of per second. With the high number of measurement particularly slow but also lose its significance. Counting of the usual eight frequency measurement 10 MHz signals, one second gate will be 10000000 Hz, which is actually seven (equivalent to the median number of common admission after the value), to obtain eight needed 10 seconds gate ; to obtain nine needed 100 seconds gate, followed by analogy, shows that even the permission of 11 need 10,000 second measurement time. But in any case, or seven per second. Therefore, to fast must be a few high speed.
Distinction: it is like a minimum voltage meter can tell how much voltage indicators are similar, the smaller the better, unit ps (picoseconds). 1000ps = 1ns. Suppose you use the frequency of 1 ns to differentiate between an e-12 error, we need a ns/1e-12 = 1000 seconds. Also assume that you have a frequency resolution of 100 ps, the measurement time can be shortened by 10 times for 100 seconds, or can be in the same 1000 second measured under an e-14 Error.
4、 Time and Frequency Measurement
Compared to traditional methods of circuit design, EDA technology uses VHDL language to describe circuit system, including circuit structure, behavior, function and interface logic. Verilog HDL description of a multi-level system hardware functions, and support top-down design features. Designers can not understand the hardware structure. Start from the system design, on the top floor of a system block diagram of the structure and design, in a diagram with Ver-ilog HDL acts on the circuit description and simulation and error correction, and then the system level verification, and finally use logic synthesis optimization tool to create specific gate-level logic circuit netlist, download to the specific FPGA device to in order to achieve FPGA design.
Time and frequency measurement is an important area of electronic measurement. Frequency and time measurement has been receiving increasing attention, length, voltage, and other parameters can be transformed into a frequency measurement and related technologies to determine. Based on the more traditional method of synchronization cycle, and has proposed a multi-cycle synchronization and quantitative method of measuring delay frequency method.
The most simple method of measuring the frequency of direct frequency measurement method. Direct Frequency Measurement is scheduled to enter the gate signal pulse, the adoption of the necessary counting circuit, the number of pulses are filled to calculate the frequency or analyte signal cycle. In the direct frequency measurement on the basis of the development of multi-cycle synchronous measurement method, in the current frequency monitoring system to be more widely used. Multi-cycle synchronization frequency measurement technology actual gate time is not fixed value, but the measured signals in the whole cycle times, and the measured signal synchronization, thereby removing the measured signal count on when the word ± 1 error, measurement accuracy greatly improved, and reached in the entire spectrum of measurement, such as precision measurement.
In the time-frequency measurement method, the multi-cycle synchronization is a high precision, but still unresolved ± a word error, mainly because of the actual gate edge and standard frequency synchronization is not filling pulse edge Tx=N0T0-△t2+△t1, if accurately measured short interval Δ t1 and Δ t2, will be able to accurately measure time intervals Tx, eliminating ± a word counting error, so as to further enhance accuracy.
To measure a short time interval Δ t1 and Δ t2, commonly used analog interpolation method with the cursor or more combined cycle synchronization, although accuracy is greatly improved, but eventually failed to resolve ± a word error this fundamental issue, but these methods equipment complex and not conducive to the promotion.
To obtain high precision, fast response time, simple structure and the frequency and time measurement method is relatively difficult.
Judging from the structure as simple as possible at the same time take into account the point of view of accuracy, multi-cycle synchronization and delay based on the quantitative methods in a short period of time interval measurement, achieved within the scope of broadband, such as high-resolution measurement accuracy.
Quantified by measuring short time intervals Delay
Photoelectric signal can be in a certain stability in the medium of rapid spread, and in different media have different delay. By signals generated by the delay to quantify, and gave a short period of time interval measurement.
The basic principle is that \count\from the traditional counter serial number, that is, to signal through a series of delay unit, the delay unit on the delay stability, under the control of the computer Delay on the state of high-speed acquisition and data processing, for a short period of time to achieve accurate measurement interval.
Delay quantitative thinking depend on the realization of the delay stability delay unit, the unit depends on the resolution of the delay time delay element.
Delay device as a unit can be passive conduit, or other active devices gate circuit. Among them, Traverse shorter delay time (nearly the speed of light transmission delay), the gate delay time longer. Taking into account delays can be predictive ability final choice of the CPLD devices, the realization of the short time interval measurement.
Will be the beginning of a short time interval signal sent delay in the
基于FPGA的数字频率计设计毕业论文
