Digital Fundamentals. Introduction to Digital Signal Processing

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1 Digital Fundamentals Introduction to Digital Signal Processing 1

2 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 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 2

3 Digital Signal Processing Basics ADC Analog-to-Digital Conversion - DSP Data Signal Processor DAC Data to-analog Conversion Figure An original analog signal (sine wave) and its stairstep approximation. 3

4 Figure Basic block diagram of a digital signal processing system. 4

5 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 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 5

6 Figure Simple illustration of the sampling process. 6

7 Figure Simple illustration of the sampling theory. 7

8 Figure A basic illustration of the condition f sample < 2f a(max). 8

9 Figure aliasing error. After low-pass filtering, the frequency spectra of the analog and the sampling signals do not overlap, thus eliminating 9

10 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 sampled value 10

11 Figure Illustration of a sample-and-hold operation. 11

12 Figure 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. 12

13 Figure reference. Sample-and-hold output waveform with four quantization levels. The original analog waveform is shown in light gray for 13

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

15 Figure for reference. Sample-and-hold output waveform with sixteen quantization levels. The original analog waveform is shown in light gray 15

16 Figure The reconstructed waveform in Figure using sixteen quantization levels (4 bits). The original analog waveform is shown in light gray for reference. 16

17 Analog-to-Digital Conversion Methods Flash (Simultaneous) Analog-to-Digital Conversion Dual-Slope Analog-to-Digital Conversion Successive-Approximation Analog-to- Digital Converter ADC0804 Analog-to-Digital Converter Sigma-Delta Analog-to-digital Converter 17

18 Figure The operational amplifier (op-amp). 18

19 Figure A 3-bit flash ADC. 19

20 Figure Example 14-1 Determine the digital output for the signal presented below. Sampling of values on a waveform for conversion to binary code. Figure Resulting digital outputs for sample-and-hold values. Output D 0 is the LSB of the 3-bit binary code. 20

21 Figure Basic dual-slope ADC. 21

22 Figure Illustration of dual-slope conversion. 22

23 Figure Successive-approximation ADC. 23

24 Figure Illustration of the successive-approximation conversion process. 24

25 Figure The ADC0804 analog-to-digital converter. 25

26 Figure A simplified illustration of sigma-delta analog-to-digital conversion. 26

27 Figure Partial functional block diagram of a sigma-delta ADC. 27

28 Figure One type of sigma-delta ADC. 28

29 Figure A method for testing ADCs. 29

30 Figure Illustrations of analog-to-digital conversion errors. 30

31 Figure Example 14-2: Identify the problem and the most probable fault 31

32 DSP (Digital Signal Processor) Programming Typically programmed in Assembly language or in C Very specialized applications with much redundancy DSPs instruction set smaller than a microprocessors 32

33 DSP Applications Telecommunications Music Processing Speech Generation and Recognition Radar Image processing Filtering 33

34 Figure The DSP has a digital input and produces a digital output. 34

35 Figure Many DSPs use the Harvard architecture (two memories). 35

36 Figure General block diagram of the TMS320C6000 series DSP. 36

37 Figure The four fetch phases of the pipeline operation. 37

38 Figure The two decode phases of the pipeline operation. 38

39 Figure The five execute phases of pipeline operation. 39

40 Figure A 352-pin BGA package. 40

41 Figure Simplified block diagram of a digital cellular phone. 41

42 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 8 functional units 2 each for multipliers, logic, shift, and data moves Packaged as a 352-pin ball grid array with CMOS technology 42

43 Digital-to-Analog Conversion Methods Binary-Weighted-Input Digital-to-Analog Converter R/2R Ladder Digital-to-Analog Converter 43

44 Figure A 4-bit DAC with binary-weighted inputs. 44

45 Figure Example 14-3: Determine the output for the following DAC Figure Output of the DAC in Figure

46 Figure An R/2R ladder DAC. 46

47 Figure Analysis of the R/2R ladder DAC. 47

48 Figure Basic test setup for a DAC. 48

49 D/A Conversion Errors Nonmonotonicity Differential Nonlinearity Low or High Gain Offset Error 49

50 Figure Illustrations of several digital-to-analog conversion errors. 50

51 Figure Example 14-5: Identify the type of error, and suggest an approach to isolate the fault 51

52 Figure The reconstruction filter smooths the output of the DAC. 52

Data Converter Overview: DACs and ADCs. Dr. Paul Hasler and Dr. Philip Allen

Data Converter Overview: DACs and ADCs Dr. Paul Hasler and Dr. Philip Allen The need for Data Converters ANALOG SIGNAL (Speech, Images, Sensors, Radar, etc.) PRE-PROCESSING (Filtering and analog to digital