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Unformatted text preview: ENEE 241 02 * READING ASSIGNMENT 18 Thu 04/16 Lecture Topics: periodic signals in continuous time; sums of harmonically related sinusoids; introduction to Fourier series Key Points: Most periodic signals in continuous time can be expressed as sums of Fourier sinusoids. For a fundamental period T and (correspondingly) fundamental frequency = 2 /T , the k th complex Fourier sinusoid (where k Z ) is given by v ( k ) ( t ) = e jk t The frequency k is referred to as the k th harmonic (of ). The complex Fourier series of period T with coefficients { S k } is defined by s ( t ) = X k = S k e jk t , provided the infinite sum converges. It is realvalued if and only if ( k Z ) S k = ( S k ) * Theory and Examples: 1 . We have seen that the DFT synthesis equation s [ n ] = 1 L L 1 X k =0 S [ k ] e jk (2 /L ) n , n = 0 : L 1 can be extended outside the time index range n = 0 : L 1 to produce an infinite periodic sequence having period L . This also means that every discretetime sequence that is periodic with period L can be expressed as a sum of L Fourier sinusoids with coefficients given by the (scaled) DFT of the segment of the sequence corresponding to time indices n = 0 : L 1. Not surprisingly, the L Fourier frequencies k = k (2 /L ) (where k = 0 : L 1) are the only distinct values of in [0 , 2 ) such that x [ n ] = e jn is periodic with period L . 2 . Most periodic signals encountered in continuous time have a similar structure. In other words, they can be written as a sum of continuoustime Fourier sinusoids, whose coefficients are obtained by an operation that resembles the DFT....
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 Spring '08
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