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Unformatted text preview: EE 3120 Chapter 3 Introduction to Discrete Time Signals and Systems Sampling C/D DT system D/C x ( t ) x [ n ] ( ) y t y [ n ] CT signal is sampled to convert to a DT signal Signal is processed by a DT system. CT signal constructed from the output sequence We can use a DT system to process a CT signal by sampling the CT signal and applying the resulting sequence to the DT systems, then constructing the output CT signal from the output sequence . ( ) y t y [ n ] Why Sample? Digital signals and systems have many benefits over analog signals. Less sensitive to changes in component and signal variations caused by temperature, manufacture tolerance. Circuits can be easily duplicated, built in high volume for low cost and built on a single chip using VLSI circuits Hardware implementation of digital filters using microprocessors and LSI Digital filters can be programmed and changed easily, more variety of filtering Digital signals can be stored in memory, accessed remotely D sigs can be coded low bit errors and encrypted for privacy D sys can be timeshared allowing for multiple inputs simultaneously (Time division multiple access, TDMA) Reproduction of D sigs can be done with NO deterioration or noise added. (photocopying an image vs. scanning) CPU speeds allow for faster and more complex (real time) digital signal processing, DSP Sampling an Analog Signal Consider an analog f(t) signal defined for all t in ( , ) sampling f(t) with sampling period or sampling rate T gives a discrete time (DT) signal: , where n is an integer ranging from to Define: is a sequence of numbers assumes T = 1 DT signals are also called sequences. . f [n] f [ n ]:= f ( nT ) f ( nT ) Example: is sampled every T = 0.1 seconds. The DT sequence would be: ( ) t x t e = 0.1 ( ) [ ] t n t nT x nT e e x n = = = = ( ) t x t e = [ ] x n Plotted for t from 2 and 2 Plotted for n from 20 to 20 t = 0 nT = 0 t n How often should we sample? The sampling rate should be selected so that the primary shape of the signal is maintained....
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 Fall '08
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