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1、信息科学与电子工程专业英语Technical EnglishFor Information Science and Electronic Engineering信息科学与电子工程专业英语Unit 9Electronics:Digital Signals and Signal Processing信息科学与电子工程专业英语Part IDigital Signal Processing 3New Wordssub-field sub-field 分领域，子领域 分领域，子领域 sonar sonar 声呐 声呐sensor array sensor array 传感器阵列 传感器阵列 biomed
2、ical biomedical 生物特征的 生物特征的algorithm algorithm 算法 算法 abbreviate abbreviate 缩写，缩略 缩写，缩略purpose-designed purpose-designed 针对目的设计的 针对目的设计的 application-specific application-specific 面向应用的 面向应用的integrated circuits integrated circuits 集成电路 集成电路 autocorrelation autocorrelation 自相关 自相关wavelet wavelet 小波 小波
3、baseband baseband 基带 基带informed informed 有知识的，有见闻的 有知识的，有见闻的 spatial domain spatial domain 空间域 空间域cross-correlation cross-correlation 互相关 互相关 interval interval 间隔 间隔discretization discretization 离散化 离散化 quantization quantization 量化 量化partition partition 分割，分区 分割，分区 finite set finite set 有限的集 有限的集4Ne
4、w Wordstheorem theorem 定理 定理 scenario scenario 情节，方案 情节，方案carrier carrier 载波 载波 ingredient ingredient 成分，因素 成分，因素demodulation demodulation 解调 解调 enhancement enhancement 增强 增强filtering filtering 滤波 滤波 weighted weighted 加权的 加权的characterize characterize 描绘，刻画性质 描绘，刻画性质 superposition superposition 叠加 叠加
5、causal causal 因果关系的 因果关系的 converge converge 收敛 收敛diverge diverge 发散 发散 bounded bounded 有界的 有界的transfer functions transfer functions 传递函数 传递函数 block diagram block diagram 方框图 方框图derive derive 推导 推导 magnitude magnitude 大小 大小cepstrum cepstrum 倒谱 倒谱 logarithm logarithm 对数 对数5New WordsFIR(finite impulser
6、esponse filter)FIR(finite impulseresponse filter)有限冲击响应滤波器 有限冲击响应滤波器IIR(infinite impulse response filter)IIR(infinite impulse response filter)无限冲击响应滤波器 无限冲击响应滤波器field-programmablegate array field-programmablegate array(FPGA)(FPGA)现场可编程门阵列 现场可编程门阵列computer aidedtomography(CAT)computer aidedtomography
7、(CAT)计算机断层扫描 计算机断层扫描seismology seismology 地震学 地震学 equalization equalization 均衡 均衡hifi(high fidelity)hifi(high fidelity)高保真（音乐）高保真（音乐）reinforcement reinforcement 加强 加强animation animation 动画 动画 loudspeaker loudspeaker 扬声器 扬声器floating point floating point 浮点 浮点 arithmetic arithmetic 算术 算术magnetic reson
8、anceimaging(MRI)magnetic resonanceimaging(MRI)磁共振成像 磁共振成像fixed-point arithmetic fixed-point arithmetic定点运算，整数运算 定点运算，整数运算61Digital signal processing(DSP)is the study of signals in a Digital signal processing(DSP)is the study of signals in a digital representation and the processing methods of these
9、digital representation and the processing methods of these signals.DSP and analog signal processing are sub-fields of signals.DSP and analog signal processing are sub-fields of signal processing.DSP includes sub-fields like signal processing.DSP includes sub-fields like audio and audio and speech si
10、gnal processing,sonar and radar signal processing,speech signal processing,sonar and radar signal processing,sensor array processing,spectral estimation,statistical signal sensor array processing,spectral estimation,statistical signal processing,image processing,signal processing for processing,imag
11、e processing,signal processing for communications,biomedical signal processing communications,biomedical signal processing,etc.,etc.音频及语音信号处理、声纳和雷达信号处理、音频及语音信号处理、声纳和雷达信号处理、传感器阵列处理、谱估计、统计信号处理、图 传感器阵列处理、谱估计、统计信号处理、图像处理、通信信号处理、生物医学信号处理 像处理、通信信号处理、生物医学信号处理72Since the goal of DSP is usually to measure or
12、 filter continuous Since the goal of DSP is usually to measure or filter continuous real-world analog signals real-world analog signals,the first step is usually to convert,the first step is usually to convert the signal from an analog to a digital form,by using an analog the signal from an analog t
13、o a digital form,by using an analog to digital converter.Often,the required output signal is to digital converter.Often,the required output signal is another analog output signal,which requires a digital to another analog output signal,which requires a digital to analog converter.analog converter.数字
14、信号处理的目标通常是 数字信号处理的目标通常是测量连续的真实世界的模拟 测量连续的真实世界的模拟信号或对其滤波 信号或对其滤波83The algorithms required for DSP are sometimes performed The algorithms required for DSP are sometimes performed using specialized computers,which make use of specialized using specialized computers,which make use of specialized micropr
15、ocessors called digital signal processors(also microprocessors called digital signal processors(also abbreviated DSP).abbreviated DSP).These process signals in real time,and are These process signals in real time,and are generally purpose-designed application-specific integrated generally purpose-de
16、signed application-specific integrated circuits(ASICs).circuits(ASICs).1 1 这些（数字信号处理器）实时处理 这些（数字信号处理器）实时处理信号，通常是针对具体目的而设计 信号，通常是针对具体目的而设计的专用集成电路（的专用集成电路（ASIC ASIC）。）。93When flexibility and rapid development are more important When flexibility and rapid development are more important than unit costs
17、at high volume,DSP algorithms may also be than unit costs at high volume,DSP algorithms may also be implemented using field-programmable gate arrays(FPGAs).implemented using field-programmable gate arrays(FPGAs).2 2当灵活性和快速开发比大批量生产的 当灵活性和快速开发比大批量生产的成本更重要时，成本更重要时，DSP DSP 算法也可以用现场 算法也可以用现场可编程门阵列来实现。可编程
18、门阵列来实现。104 DSP domainsIn DSP,engineers usually study digital signals in one of the In DSP,engineers usually study digital signals in one of the following domains:time domain(one-dimensional signals),following domains:time domain(one-dimensional signals),spatial domain(multidimensional signals),frequ
19、ency domain,spatial domain(multidimensional signals),frequency domain,autocorrelation domain,and wavelet domains.autocorrelation domain,and wavelet domains.They choose They choose the domain in which to process a signal by making an the domain in which to process a signal by making an informed guess
20、(or by trying different possibilities)as to which informed guess(or by trying different possibilities)as to which domain best represents the essential characteristics of the domain best represents the essential characteristics of the signal.signal.3 3 他们按某些依据来猜测（或试验不同的可能 他们按某些依据来猜测（或试验不同的可能性）那一个域能够最
21、好地表示信号的本质特 性）那一个域能够最好地表示信号的本质特性来选择在其中进行信号处理的域。性来选择在其中进行信号处理的域。1 14A sequence of samples from a measuring device produces a A sequence of samples from a measuring device produces a time or spatial domain representation,whereas a discrete time or spatial domain representation,whereas a discrete Fourie
22、r transform produces the frequency domain Fourier transform produces the frequency domain information,that is,the frequency spectrum.information,that is,the frequency spectrum.4 4 Autocorrelation Autocorrelation is defined as the cross-correlation of the signal with itself over is defined as the cro
23、ss-correlation of the signal with itself over varying intervals of time or space.varying intervals of time or space.从测量设备得到的样本序列产生（信号的）从测量设备得到的样本序列产生（信号的）时域或空域表示，而离散 时域或空域表示，而离散Fourier Fourier 变换则产 变换则产生频域表示即频谱。生频域表示即频谱。125 Signal samplingWith the increasing use of computers the usage and need of Wi
24、th the increasing use of computers the usage and need of digital signal processing has increased.In order to use an digital signal processing has increased.In order to use an analog signal on a computer it must be digitized with an analog signal on a computer it must be digitized with an analog to d
25、igital converter(ADC).analog to digital converter(ADC).Sampling is usually carried Sampling is usually carried out in two stages,discretization and quantization out in two stages,discretization and quantization.采样通常分两步实现：采样通常分两步实现：离散化和量化 离散化和量化135In the discretization stage,the space of signals is p
26、artitioned In the discretization stage,the space of signals is partitioned into equivalence classes and discretization is carried out by into equivalence classes and discretization is carried out by replacing the signal with representative signal of the replacing the signal with representative signa
27、l of the corresponding equivalence class.corresponding equivalence class.5 5 In the quantization stage In the quantization stage the the representative signal values are approximated by values from representative signal values are approximated by values from a finite set a finite set.在离散化阶段，信号空间被分割为
28、 在离散化阶段，信号空间被分割为相等的区间，用相应区间的代表性 相等的区间，用相应区间的代表性信号值代替信号本身。信号值代替信号本身。用有限集中的值来近似代表 用有限集中的值来近似代表性的信号值 性的信号值146In order for a sampled analog signal to be exactly In order for a sampled analog signal to be exactly reconstructed,the Nyquist-Shannon sampling theorem must reconstructed,the Nyquist-Shannon sa
29、mpling theorem must be satisfied.be satisfied.This theorem states that the sampling frequency This theorem states that the sampling frequency must be greater than twice the bandwidth of the signal must be greater than twice the bandwidth of the signal.定理规定：采样频率必须 定理规定：采样频率必须大于两倍的信号带宽 大于两倍的信号带宽156In
30、practice,In practice,the sampling frequency is often significantly more the sampling frequency is often significantly more than twice the required bandwidth than twice the required bandwidth.The most common.The most common bandwidth scenarios are:DCBW(“baseband”);and bandwidth scenarios are:DCBW(“ba
31、seband”);and fc fc BW,BW,a frequency band centered on a carrier frequency(“direct a frequency band centered on a carrier frequency(“direct demodulation”).demodulation”).采样频率通常远大于信号 采样频率通常远大于信号带宽的两倍 带宽的两倍167A digital to analog converter(DAC)is used to convert the A digital to analog converter(DAC)is
32、used to convert the digital signal back to analog.The use of a digital computer is a digital signal back to analog.The use of a digital computer is a key ingredient into digital control systems.key ingredient into digital control systems.178 Time and space domainsThe most common processing approach
33、in the time or space The most common processing approach in the time or space domain is enhancement of the input signal through a method domain is enhancement of the input signal through a method called filtering.called filtering.Filtering generally consists of some Filtering generally consists of s
34、ome transformation of a number of surrounding samples around transformation of a number of surrounding samples around the current sample of the input or output signal the current sample of the input or output signal.There are.There are various ways to characterize filters;for example:various ways to
35、 characterize filters;for example:滤波通常由在输入或输出信号当前样本 滤波通常由在输入或输出信号当前样本周围的许多样本的某种变换组成 周围的许多样本的某种变换组成188-A“linear”filter is a linear transformation of input A“linear”filter is a linear transformation of input samples;other filters are“non-linear.”samples;other filters are“non-linear.”Linear filters sat
36、isfy Linear filters satisfy the superposition condition,i.e.,if an input is a weighted the superposition condition,i.e.,if an input is a weighted linear combination of different signals,the output is an linear combination of different signals,the output is an equally weighted linear combination of t
37、he corresponding equally weighted linear combination of the corresponding output signals.output signals.6 6 线性滤波器满足叠加条件，就是说，如果输入 线性滤波器满足叠加条件，就是说，如果输入是不同信号的加权线性组合，输出就是（各信 是不同信号的加权线性组合，输出就是（各信号）相应输出的同样加权线性组合。号）相应输出的同样加权线性组合。198-A“causal”filter uses only previous samples of the input or A“causal”filter
38、 uses only previous samples of the input or output signals;while a“non-causal”filter uses future input output signals;while a“non-causal”filter uses future input samples.A non-causal filter can usually be changed into a samples.A non-causal filter can usually be changed into a causal filter by addin
39、g a delay to it.causal filter by adding a delay to it.-A“time-invariant”filter has constant properties over time;A“time-invariant”filter has constant properties over time;other filters such as adaptive filters change in time other filters such as adaptive filters change in time.“时不变 时不变”滤波器对时间具有不变的性
40、质，滤波器对时间具有不变的性质，诸如自适应滤波器等其它滤波器随时间而 诸如自适应滤波器等其它滤波器随时间而改变 改变208-Some filters are“stable”,others are“unstable”.Some filters are“stable”,others are“unstable”.A stable A stable filter produces an output that converges to a constant value filter produces an output that converges to a constant value with t
41、ime,or remains bounded within a finite interval with time,or remains bounded within a finite interval.An.An unstable filter produces output which diverges.unstable filter produces output which diverges.稳定的滤波器产生的输出随时间收敛于一个 稳定的滤波器产生的输出随时间收敛于一个不变的值，或在有限的时间间隔内保持有界 不变的值，或在有限的时间间隔内保持有界218-A“finite impulse
42、 response”(FIR)filter uses only the input A“finite impulse response”(FIR)filter uses only the input signal,signal,while an“infinite impulse response”filter(IIR)uses while an“infinite impulse response”filter(IIR)uses both the input signal and previous samples of the output both the input signal and p
43、revious samples of the output signal signal.FIR filters are always stable,while IIR filters may.FIR filters are always stable,while IIR filters may be unstable.be unstable.而无限脉冲响应（而无限脉冲响应（IIR IIR）滤波器）滤波器同时使用输入信号和以前的输出 同时使用输入信号和以前的输出信号样本 信号样本229Most filters can be described in Z-domain(a superset of
44、the Most filters can be described in Z-domain(a superset of the frequency domain)by their transfer functions.frequency domain)by their transfer functions.A filter may A filter may also be described as a difference equation,a collection of also be described as a difference equation,a collection of ze
45、roes and poles or,if it is an FIR filter,an impulse response or zeroes and poles or,if it is an FIR filter,an impulse response or step response.step response.7 7 滤波器也可以用差分方程或一组零极点 滤波器也可以用差分方程或一组零极点表示，对于 表示，对于FIR FIR 滤波器还可以用冲击响应 滤波器还可以用冲击响应或阶跃响应表示。或阶跃响应表示。239The output of an FIR filter to any given i
46、nput may be The output of an FIR filter to any given input may be calculated by convolving the input signal with the impulse calculated by convolving the input signal with the impulse response.response.Filters can also be represented by block diagrams Filters can also be represented by block diagram
47、s which can then be used to derive a sample processing which can then be used to derive a sample processing algorithm to implement the filter using hardware instructions algorithm to implement the filter using hardware instructions.滤波器还可以用结构图来表示，它能 滤波器还可以用结构图来表示，它能用来推导样本处理算法，以便使用硬 用来推导样本处理算法，以便使用硬件指
48、令实现滤波器 件指令实现滤波器2410 Frequency domainSignals are converted from time or space domain to the Signals are converted from time or space domain to the frequency domain usually through the Fourier transform.frequency domain usually through the Fourier transform.The The Fourier transform converts the signa
49、l information to a Fourier transform converts the signal information to a magnitude and phase component of each frequency magnitude and phase component of each frequency.Often the.Often the Fourier transform is converted to the power spectrum,which Fourier transform is converted to the power spectru
50、m,which is the magnitude of each frequency component squared.is the magnitude of each frequency component squared.Fourier Fourier 变换将信号信息变换成每个 变换将信号信息变换成每个频率的幅度和相位成分 频率的幅度和相位成分2511The most common purpose for analysis of signals in the The most common purpose for analysis of signals in the frequency