Digital Fundamentals - Electronics Research...

Digital Fundamentals

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Introduction to Digital Signal Processing

Objectives

•List the essential elements in a digital signal processing system

•Explain how analog signals are converted to digital form

•Discuss the purpose of filtering

•Describe the sampling process

•State the purposes of analog-to-digital conversion

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•Explain how several types of ADCs operate

•Explain the basic concepts of a digital signal processor (DSP)

•Describe the basic architecture of a DSP

•Name some of the functions that a DSP performs

•State the purpose of digital-to-analog conversion

•Explain how DACs operate

Digital Signal Processing Basics

• ADC – Analog-to-Digital Conversion -

• DSP – Data Signal Processor

• DAC Data –to-Analog Conversion

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Figure 14--1 An original analog signal (sine wave) and its “stairstep” approximation.

Thomas L. FloydDigital Fundamentals, 8e

Copyright ©2003 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

Figure 14--2 Basic block diagram of a digital signal processing system.

4Thomas L. FloydDigital Fundamentals, 8e



Converting Analog Signals to Digital

• Filtering – first step before an A/D conversion, removes unwanted frequencies, called pre-filtering

• Sampling – The process of converting an analog signal into a series of impulses representing the amplitude of the signal at a given time

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signal at a given time• Sampling frequency – should be at least twice the highest

analog frequency• Nyquist limit or Nyquist frequency – if the sampling rate

is less than 2 times the highest analog frequency and effect called aliasing where frequencies are generated by the sampling process that cause interference problems

• Hold – After the signal is sampled it is applied to a hold circuit

Figure 14--3 Simple illustration of the sampling process.




Figure 14--4 Simple illustration of the sampling theory.




Figure 14--5 A basic illustration of the condition fsample< 2fa(max).




Figure 14--6 After low-pass filtering, the frequency spectra of the analog and the sampling signals do not overlap, thus eliminating aliasing error.




Converting Analog Signals to Digital continued

• Convert the sample-hold signal to a digital circuit

• Quantization – during the quantization process a binary code is assigned to each

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process a binary code is assigned to each sampled value

Figure 14--7 Illustration of a sample-and-hold operation.




Figure 14--8 Basic function of an analog-to-digital (ADC) converter (The binary codes and number of bits are arbitrarily chosen for illustration only). The ADC output waveform that represents the binary codes is also shown.




Figure 14--9 Sample-and-hold output waveform with four quantization levels. The original analog waveform is shown in light gray for reference.




Figure 14--10 The reconstructed waveform in Figure 14-9 using four quantization levels (2 bits). The original analog waveform is shown in light gray for reference.




Figure 14--11 Sample-and-hold output waveform with sixteen quantization levels. The original analog waveform is shown in light gray for reference.




Figure 14--12 The reconstructed waveform in Figure 14-11 using sixteen quantization levels (4 bits). The original analog waveform is shown in light gray for reference.




Analog-to-Digital Conversion Methods

• Flash (Simultaneous) Analog-to-Digital Conversion

• Dual-Slope Analog-to-Digital Conversion

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• Successive-Approximation Analog-to-Digital Converter

• ADC0804 Analog-to-Digital Converter

• Sigma-Delta Analog-to-digital Converter

Figure 14--13 The operational amplifier (op-amp).




Figure 14--14 A 3-bit flash ADC.




Figure 14-15 Example 14-1 Determine the digital output for the signal presented below. Sampling of values on a waveform for conversion to binary code.




Figure 14--16 Resulting digital outputs for sample-and-hold values. Output D0 is the LSB of the 3-bit binary code.

Figure 14--17 Basic dual-slope ADC.




Figure 14--18 Illustration of dual-slope conversion.




Figure 14--19 Successive-approximation ADC.




Figure 14--20 Illustration of the successive-approximation conversion process.




Figure 14--21 The ADC0804 analog-to-digital converter.




Figure 14--22 A simplified illustration of sigma-delta analog-to-digital conversion.




Figure 14--23 Partial functional block diagram of a sigma-delta ADC.




Figure 14--24 One type of sigma-delta ADC.




Figure 14--25 A method for testing ADCs.




Figure 14--26 Illustrations of analog-to-digital conversion errors.




Figure 14-27 Example 14-2: Identify the problem and the most probable fault




DSP (Digital Signal Processor) Programming

• Typically programmed in Assembly language or in C

• Very specialized applications with much redundancy

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redundancy

• DSPs instruction set smaller than a microprocessors

DSP Applications

• Telecommunications

• Music Processing

• Speech Generation and Recognition

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• Speech Generation and Recognition

• Radar

• Image processing

• Filtering

Figure 14-28 The DSP has a digital input and produces a digital output.




Figure 14--29 Many DSPs use the Harvard architecture (two memories).




Figure 14--30 General block diagram of the TMS320C6000 series DSP.




Figure 14--31 The four fetch phases of the pipeline operation.




Figure 14--32 The two decode phases of the pipeline operation.




Figure 14--33 The five execute phases of pipeline operation.




Figure 14--34 A 352-pin BGA package.




Figure 14--35 Simplified block diagram of a digital cellular phone.




TMS320C6000 Series DSP

• CPU with 64 general purpose 32 bit registers in C64xx

• CPU with 32 general purpose 32 bit registers in C62xx and C67xx

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registers in C62xx and C67xx• 8 functional units 2 each for multipliers,

logic, shift, and data moves• Packaged as a 352-pin ball grid array with

CMOS technology

Digital-to-Analog Conversion Methods

• Binary-Weighted-Input Digital-to-Analog Converter

• R/2R Ladder Digital-to-Analog Converter

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Figure 14--36 A 4-bit DAC with binary-weighted inputs.




Figure 14-37 Example 14-3: Determine the output for the following DAC

Figure 14--38 Output of the DAC in Figure 14-37.




Figure 14--39 An R/2R ladder DAC.




Figure 14--40 Analysis of the R/2R ladder DAC.


Figure 14--41 Basic test setup for a DAC.




D/A Conversion Errors

• Nonmonotonicity

• Differential Nonlinearity

• Low or High Gain

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• Low or High Gain

• Offset Error

Figure 14--42 Illustrations of several digital-to-analog conversion errors.




Figure 14-43 Example 14-5: Identify the type of error, and suggest an approach to isolate the fault




Figure 14--44 The reconstruction filter smooths the output of the DAC.




Digital Fundamentals - Electronics Research...

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