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1、Unit 9 Digital Signal Processing,Passage C Comparison of DSP and ASP,9单元 数字信号处理,C篇 比较DSP和ASP,学号：20107600 姓名：章太元,Passage C Comparison of DSP and ASPSignals may be processed using analog techniques(analog signal processing,or ASP),digital techniques(digital signal processing,or DSP),or a combination o
2、f analog and digital techniques(mixed signal processing,or MSP).In some cases,the choice of techniques is clear;in others,there is no clear cut choice,and second-order considerations may be used to make the final decision.With respect to DSP,the factor that distinguishes it from traditional computer
3、 analysis of data is its speed and efficiency in performing sophisticated digital processing functions such as filtering,FFT analysis,and data compression in real time.,信号可以用模拟技术处理（模拟信号处理，数字技术（或ASP），数字信号处理，或DSP），或一个组合的模拟和数字技术（混合信号处理，或MSP）。在某些情况下，技术的选择是明确的；在其他情况下，没有明确的选择，和二阶考虑可以用来做最后的决定。对于DSP，使得它与传统计
4、算机数据分析是它的速度和效率，进行复杂的数字处理功能，如滤波，FFT分析，数据的实时压缩,The term mixed signal processing implies that both analog and digital processing is done as part of the system.The system may be implemented in the form of a printed circuit board or a single integrated circuit chip.In the context of this broad definition
5、,ADCs and DACs are considered to be mixed signal processors,since both analog and digital functions are implemented in each.Recent advances in Very Large Scale Integration(VLSI)processing technology allow complex digital processing as well as analog processing to be performed on the same chip.The ve
6、ry nature of DSP itself implies that these functions can be performed in real-time.,术语混合信号处理意味着，模拟和数字处理系统的一部分。该系统可在印刷电路板或一个单一的集成电路芯片的形式实现。在这个广泛的定义下，ADC和DAC被认为是混合信号处理器，由于模拟和数字功能的实现在每个。在超大规模集成电路（VLSI）处理技术的进展使得复杂的数字信号处理和模拟处理的是在同一芯片上进行。DSP本身的性质意味着，这些功能可以在实时执行。,ASP vs.DSP Todays engineer faces a challeng
7、e in selecting the proper mix of analog and digital techniques to solve the signal processing task at hand.It is impossible to process real-world analog signals using purely digital techniques,since all sensors(microphones,thermocouples,strain gages,piezoelectric crystals,disk drive heads,etc.)are a
8、nalog sensors.Therefore,some sort of signal conditioning circuitry is required in order to prepare the sensor output for further signal processing,whether it be analog or digital.Signal conditioning circuits are,in reality,analog signal processors,performing such functions as multiplication(gain),is
9、olation(instrumentation amplifiers and isolation amplifiers),detection in the presence of noise(high common-mode instrumentation amplifiers etc.),dynamic range compression(log amps,LOGDACs,and programmable gain amplifiers),and filtering(both passive and active).Several methods of accomplishing signa
10、l processing are shown in Figure 9.5.The top portion of the figure shows the purely analog approach.The latter parts of the figure show the DSP approach.Note that once the decision has been made to use DSP techniques,the next decision must be where to place the ADC in the signal path.,ASP与DSP今天的工程师在
11、选择适当的混合模拟和数字技术来解决手头的信号处理任务所面临的挑战。这是不可能的真实世界的模拟信号处理采用纯数字技术，因为所有的传感器（麦克风，热电偶，应变计，压电晶体，磁盘驱动器的磁头，等）是模拟传感器。因此，某种形式的信号调理电路是为了准备传感器输出信号进一步处理，无论是模拟或数字。信号调理电路，在现实中，模拟信号处理器，如乘法执行这些功能（增益），隔离（仪表放大器和隔离放大器），在存在噪声检测（高共模仪表放大器等），动态范围压缩（对数放大器，logdacs，和可编程增益放大器），和过滤（包括被动和主动的）。完成信号处理的几种方法，如图9.5所示。图中的顶部显示纯模拟方法。图中的一部分显示的
12、数字信号处理方法。请注意，一旦决定已经做出，采用DSP技术，未来的决定必须在什么地方ADC的信号路径。,Figure 9.5 Some Methods of Accomplishing Signal Processing,In general,as the ADC is moved closer to the actual sensor,more of the analog signal conditioning burden is now placed on the ADC.The added ADC complexity may take the form of increased sam
13、pling rate,wider dynamic range,higher resolution,input noise rejection,input filtering and programmable gain amplifiers(PGAs),on-chip voltage references,etc.,all of which add functionality and simplify the system.With todays high-resolution/high sampling rate data converter technology,significant pr
14、ogress has been made in integrating more and more of the conditioning circuitry within the ADC/DAC itself.,In the measurement area,for instance,24-bit ADCs are available with built-in programmable gain amplifiers(PGAs)which allow full-scale bridge signals of 10 mV to be digitized directly with no fu
15、rther conditioning.At voiceband and audio frequencies,complete coder-decoders(Codecs or Analog Front Ends)are available which have sufficient on-chip analog circuitry to minimize the requirement for external conditioning components.At video speeds,analog front ends are also available for such applic
16、ations as CCD image processing and others.,在一般情况下，作为ADC接近实际的传感器，更多的模拟信号调理的负担，现在放在ADC。增加ADC的复杂性可以增加采样率的形式，更宽的动态范围，高分辨率，输入噪声排斥，输入滤波和可编程增益放大器（PGA），片上的参考电压，等等，所有这些新增功能和简化系统。今天的高分辨率、高采样率的数据转换技术，在集成越来越多的调理电路内的ADC/DAC本身取得了明显的进展。在测量领域，例如，24位ADC提供内置的可编程增益放大器（PGA）允许10 MV全桥被数字化的信号直接没有进一步的调节。在音频和音频解码器（编解码器或编码器，
17、完整模拟前端）可有足够的片上模拟电路，以尽量减少对外部条件的要求。在视频的速度，模拟前端也可用于CCD图像处理和其他的应用程序。,A practical example As a practical example of the power of DSP,consider the comparison between an analog and a digital lowpass filter,each with a cutoff frequency of 1 kHz.The digital filter is implemented in a typical sampled data sys
18、tem shown in Figure 9.6.Note that thereare several implicit requirements in the diagram.First,it is assumed that an ADC/DAC combination is available with sufficient sampling frequency,resolution,and dynamic range to accurately process the signal.Second,the DSP must be fast enough to complete all its
19、 calculations within the sampling interval,1/fs.Third,analog filters are still required at the ADC input and DAC output for anti-aliasing and anti-imaging,but the performance demands are not as great.Assuming these conditions have been met,the following offers a comparison between the digital and an
20、alog filters.,一个实际的例子作为一种实用的DSP的电源的例子，考虑一个模拟和数字低通滤波器之间的比较，各有一个截止频率为1千赫。The digital filter is implemented in a typical sampled data system shown in Figure 9.6.注意，图中的一些隐含的要求thereare。First,it is assumed that an ADC/DAC combination is available with sufficient sampling frequency,resolution,and dynamic r
21、ange to accurately process the signal.第二，DSP必须足够快的采样间隔内完成所有的计算，1/FS。第三，模拟滤波器仍在ADC的输入和抗混叠和反成像DAC输出所需的，但性能的要求是不一样大。Assuming these conditions have been met,the following offers a comparison between the digital and analog filters.,Figure 9.6 A Typical Sampled Data System,The required cutoff frequency of
22、 both filters is 1 kHz.The analog filter is realized as a 6-pole Chebyshev Type 1 filter(ripple in passband,no ripple in stopband),and the response is shown in Figure 9.7.In practice,this filter would probably be realized using three 2-pole stages,each of which requires an op amp,and several resisto
23、rs and capacitors.Modern filter design CAD packages make the 6-pole design relatively straightforward,but maintaining the 0.5 dB ripple specification requires accurate component selection and matching.,两个滤波器的截止频率是1千赫的要求。模拟滤波器的实现为6极切比雪夫型滤波器（1通带阻带纹波，无纹波），和响应如图9.7所示。在实践中，该过滤器可能会使用三极阶段实现，每一个都需要一个运算放大器，和
24、几个电阻和电容器。现代CAD软件包过滤器的设计使六极设计相对简单，但保持0.5 dB的纹波规格要求准确的组件选择与匹配。,Figure 9.7 The Magnitude Response in dB,On the other hand,the 129-tap digital FIR filter shown has only 0.002 dB passband ripple,linear phase,and a much sharper roll off.In fact,it could not be realized using analog techniques!Another obvi
25、ous advantage is that the digital filter requires no component matching,and it is not sensitive to drift since the clock frequencies are crystal controlled.The 129-tap filter requires 129 MACs in order to compute an output sample.This processing must be completed within the sampling interval,1/fs,in
26、 order to maintain real-time operation.In this example,the sampling frequency is 10 kSPS,therefore 100 s is available for processing,assuming no significant additional overhead requirement.Most DSPs can complete the entire multiply-accumulate process(and other functions necessary for the filter)in a
27、 single instruction cycle.,另一方面，129个抽头的FIR数字滤波器具有0.002 dB通带纹波，线性相位，和一个更清晰的滚。事实上，它不可能使用模拟技术的实现！另一个明显的优势是，数字滤波器不需要匹配，它是不敏感的漂移由于时钟频率晶体控制。129抽头滤波器需要129个苹果来计算的输出样本。这样的处理必须在采样间隔内完成，1/FS，为了保持实时操作。在本例中，采样频率为10 kSPS的，因此100的有效处理，假设没有显着的额外的开销的要求。大多数的DSP可以完成整个乘法累加过程（和其他必要的过滤功能）在一个单一的指令周期。,Therefore,a 129-tap fi
28、lter requires that the instruction rate be greater than 129/100 s=1.3 million instructions per second(MIPS)DSPs are available with instruction rates much greater than this,so the DSP certainly is not the limiting factor in this applicationIn a practical application,there are certainly many other fac
29、tors to consider when evaluating analog versus digital filters,or analog versus digital signal processing in general.Most modern signal processing systems use a combination of analog and digital techniques in order to accomplish the desired function and take advantage of the best of both the analog and the digital world.,因此，一个129抽头滤波器要求教学率应大于129/100S=1300000指令每秒（MIPS）。DSP可与指令率比这大得多，所以DSP当然不是在该应用程序中的限制因素。在实际应用中，有一定的评估时，模拟与数字滤波器考虑多种因素的影响，或模拟与数字信号处理的一般。大多数现代信号处理系统，用来模拟和数字技术的组合来完成预期的功能，利用最好的模拟和数字世界。,
