Digital Signal Processing: Pulse Modulation and Character Coding, Slides of Control Systems Analysis

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Formatting and Baseband Modulation

Chapter 2

Formatting and Baseband Modulation

Overview

 Formatting:  Character Coding  Sampling  Quantization  Pulse Code Modulation (PCM)  Baseband signaling  PCM Waveforms (line codes)  Non-Return to Zero (NRZ), Return to Zero, Phase encoded, Multilevel binary.  M-ary Pulse Modulation  PAM, PPM, PDM  Formatting:  Character Coding  Sampling  Quantization  Pulse Code Modulation (PCM)  Baseband signaling  PCM Waveforms (line codes)  Non-Return to Zero (NRZ), Return to Zero, Phase encoded, Multilevel binary.  M-ary Pulse Modulation  PAM, PPM, PDM

Messages, Characters and Symbols

 Each textual information is composed of messages.  Messages are the combination of characters.  Characters are converted into character codes.  Character codes are converted into bits.  Bits are concatenated to form symbols. k bits combines to make M= k Symbols.  A symbol using a symbol set size of M is referred to as an M-ary System.  k=1, M=2, Two possible waveforms, Symbol length =1.  k=2, M=4, Four possible waveforms, Symbol length =2.  Each textual information is composed of messages.  Messages are the combination of characters.  Characters are converted into character codes.  Character codes are converted into bits.  Bits are concatenated to form symbols. k bits combines to make M= k Symbols.  A symbol using a symbol set size of M is referred to as an M-ary System.  k=1, M=2, Two possible waveforms, Symbol length =1.  k=2, M=4, Four possible waveforms, Symbol length =2.

2. Formatting Analog Information.

 If character encoding is not possible, information is converted into digital using two steps:  Sampling  Collecting Amplitude of the signal at different time intervals.  Qunatization:  Assigning each sample a particular code.  Both sampling and quantization results in Pulse Code Modulation (PCM).  If character encoding is not possible, information is converted into digital using two steps:  Sampling  Collecting Amplitude of the signal at different time intervals.  Qunatization:  Assigning each sample a particular code.  Both sampling and quantization results in Pulse Code Modulation (PCM).

Sampling

 Sampling can simply be done by a switching operation.  Sample and hold (transistor and capacitor) approach is used avoid any fluctuations between two consecutive samples.  The output of the sampling process is called Pulse Amplitude Modulation.  How frequently the samples should be taken so that a closely approximated analog signal can be re-generated?  Answer is Sampling theorem.  Sampling can simply be done by a switching operation.  Sample and hold (transistor and capacitor) approach is used avoid any fluctuations between two consecutive samples.  The output of the sampling process is called Pulse Amplitude Modulation.  How frequently the samples should be taken so that a closely approximated analog signal can be re-generated?  Answer is Sampling theorem.

Impulse Sampling

Impulse Sampling: Aliasing

Fourier Series computation

3.Flat-top sampling: Sample and hold

operation.

 Compatible with a digital system since the amplitude of each sample has finite number of possible values.  Input signal is continuously sampled and then the value is held for as long as it takes to for the A/D to acquire its value.  Compatible with a digital system since the amplitude of each sample has finite number of possible values.  Input signal is continuously sampled and then the value is held for as long as it takes to for the A/D to acquire its value.

Aliasing: A problem

Reason:

 Aliasing occurs due to under sampling (i.e. fs <

2B ) of the analog signal.