Table 1: Properties of the Continuous-Time Fourier Series x(t) = +∞Xk=−∞ akejk!0t = +∞Xk=−∞ akejk(2/T)t ak = 1 T ZT x(t)e−jk!0tdt = 1 T ZT x(t)e−jk(2/T)tdt Property Periodic Signal Fourier Series Coefficients x(t) y(t) Periodic with period T and fundamental frequency !0 = 2/T ak bk Linearity Ax(t) + By(t) Aak + Bbk Time-Shifting x(t − t0) ake−jk!0t0 = ake−jk(2/T)t0 Frequency-Shifting ejM!0t = ejM(2/T)tx(t) ak−M Conjugation x∗(t) a∗ −k Time Reversal x(−t) a−k Time Scaling x(t), > 0 (periodic with period T/) ak Periodic Convolution ZT x( )y(t − )d Takbk Multiplication x(t)y(t) +∞X l=−∞ albk−l Differentiation dx(t) dt jk!0ak = jk 2 T ak Integration Z t −∞ x(t)dt (finite-valued and periodic only if a0 = 0) 1 jk!0ak = 1 jk(2/T)ak Conjugate Symmetry for Real Signals x(t) real ak = a∗ −k ℜe{ak} = ℜe{a−k} ℑm{ak} = −ℑm{a−k} |ak| = |a−k| <) ak = −<) a−k Real and Even Sig- nals x(t) real and even ak real and even Real and Odd Signals x(t) real and odd ak purely imaginary and odd Even-Odd Decompo- sition of Real Signals xe(t) = Ev{x(t)} [x(t) real] xo(t) = Od{x(t)} [x(t) real] ℜe{ak} jℑm{ak} Parseval’s Relation for Periodic Signals 1 T ZT |x(t)|2dt = +∞Xk=−∞ |ak|2 Table 2: Properties of the Discrete-Time Fourier Series x[n] = X k=<N> akejk!0n = X k=<N> akejk(2/N)n ak = 1 N X n=<N> x[n]e−jk!0n = 1 N X n=<N> x[n]e−jk(2/N)n Property Periodic signal Fourier series coefficients x[n] y[n] Periodic with period N and fun- damental frequency !0 = 2/N ak bk Periodic with period N Linearity Ax[n] + By[n] Aak + Bbk Time shift x[n − n0] ake−jk(2/N)n0 Frequency Shift ejM(2/N)nx[n] ak−M Conjugation x∗[n] a∗ −k Time Reversal x[−n] a−k Time Scaling x(m)[n] = x[n/m] if n is a multiple of m 0 if n is not a multiple of m 1 m ak viewed as periodic with period mN ! (periodic with period mN) Periodic Convolution Xr=hNi x[r]y[n − r] Nakbk Multiplication x[n]y[n] Xl=hNi albk−l First Difference x[n] − x[n − 1] (1 − e−jk(2/N))ak Running Sum nX k=−∞ x[k] finite-valued and periodic only if a0 = 0 1 (1 − e−jk(2/N))ak Conjugate Symmetry for Real Signals x[n] real ak = a∗ −k ℜe{ak} = ℜe{a−k} ℑm{ak} = −ℑm{a−k} |ak| = |a−k| <) ak = −<) a−k Real and Even Signals x[n] real and even ak real and even Real and Odd Signals x[n] real and odd ak purely imaginary and odd Even-Odd Decomposi- tion of Real Signals xe[n] = Ev{x[n]} [x[n] real] xo[n] = Od{x[n]} [x[n] real] ℜe{ak} jℑm{ak} Parseval’s Relation for Periodic Signals 1 N Xn=hNi |x[n]|2 = Xk=hNi |ak|2 Table 3: Properties of the Continuous-Time Fourier Transform x(t) = 1 2 Z ∞ −∞ X(j!)ej!td! X(j!) = Z ∞ −∞ x(t)e−j!tdt Property Aperiodic Signal Fourier transform x(t) X(j!) y(t) Y (j!) Linearity ax(t) + by(t) aX(j!) + bY (j!) Time-shifting x(t − t0) e−j!t0X(j!) Frequency-shifting ej!0tx(t) X(j(! − !0)) Conjugation x∗(t) X∗(−j!) Time-Reversal x(−t) X(−j!) Time- and Frequency-Scaling x(at) 1 |a| X j! a Convolution x(t) ∗ y(t) X(j!)Y (j!) Multiplication x(t)y(t) 1 2 X(j!) ∗ Y (j!) Differentiation in Time d dt x(t) j!X(j!) Integration Z t −∞ x(t)dt 1 j! X(j!) + X(0)(!) Differentiation in Frequency tx(t) j d d! X(j!) Conjugate Symmetry for Real Signals x(t) real X(j!) = X∗(−j!) ℜe{X(j!)} = ℜe{X(−j!)} ℑm{X(j!)} = −ℑm{X(−j!)} |X(j!)| = |X(−j!)| <)X(j!) = −<)X(−j!) Symmetry for Real and Even Signals x(t) real and even X(j!) real and even Symmetry for Real and Odd Signals x(t) real and odd X(j!) purely imaginary and odd Even-Odd Decomposition for Real Signals xe(t) = Ev{x(t)} [x(t) real] xo(t) = Od{x(t)} [x(t) real] ℜe{X(j!)} jℑm{X(j!)} Parseval’s Relation for Aperiodic Signals Z +∞ −∞ |x(t)|2dt = 1 2 Z +∞ −∞ |X(j!)|2d! Table 4: Basic Continuous-Time Fourier Transform Pairs Fourier series coefficients Signal Fourier transform (if periodic) +∞X k=−∞ akejk!0t 2 +∞X k=−∞ ak(! − k!0) ak ej!0t 2(! − !0) a1 = 1 ak = 0, otherwise cos !0t [(! − !0) + (! + !0)] a1 = a−1 = 1 2 ak = 0, otherwise sin !0t
j [(! − !0) − (! + !0)] a1 = −a−1 = 1 2j ak = 0, otherwise x(t) = 1 2(!) a0 = 1, ak = 0, k 6= 0 this is the Fourier series rep- resentation for any choice of T > 0 ! Periodic square wave x(t) = 1, |t| < T1 0, T1 < |t| ≤ T 2 and x(t + T) = x(t) +∞X k=−∞ 2 sin k!0T1 k (! − k!0) !0T1
sinc k!0T1 = sin k!0T1 k +∞Xn=−∞ (t − nT) 2 T +∞X k=−∞ ! − 2k T ak = 1 T for all k x(t) 1, |t| < T1 0, |t| > T1 2 sin !T1 ! — sinWt t X(j!) = 1, |!| < W 0, |!| > W — (t) 1 — u(t) 1 j! + (!) — (t − t0) e−j!t0 — e−atu(t),ℜe{a} > 0 1 a + j! — te−atu(t),ℜe{a} > 0 1 (a + j!)2 — tn−1 (n−1)!e−atu(t), ℜe{a} > 0 1 (a + j!)n — Table 5: Properties of the Discrete-Time Fourier Transform x[n] = 1 2 Z2 X(ej!)ej!nd! X(ej!) = +∞ X n=−∞ x[n]e−j!n Property Aperiodic Signal Fourier transform x[n] y[n] X(ej!) Y (ej!) Periodic with period 2 Linearity ax[n] + by[n] aX(ej!) + bY (ej!) Time-Shifting x[n − n0] e−j!n0X(ej!) Frequency-Shifting ej!0nx[n] X(ej(!−!0)) Conjugation x∗[n] X∗(e−j!) Time Reversal x[−n] X(e−j!) Time Expansions x(k)[n] = x[n/k], if n = multiple of k 0, if n 6= multiple of k X(ejk!) Convolution x[n] ∗ y[n] X(ej!)Y (ej!) Multiplication x[n]y[n] 1 2 Z2 X(ej)Y (ej(!−))d Differencing in Time x[n] − x[n − 1] (1 − e−j!)X(ej!) Accumulation nX k=−∞ x[k] 1 1 − e−j!X(ej!) +X(ej0) +∞Xk=−∞ (! − 2k) Differentiation in Frequency nx[n] j dX(ej!) d! Conjugate Symmetry for Real Signals x[n] real X(ej!) = X∗(e−j!) ℜe{X(ej!)} = ℜe{X(e−j!)} ℑm{X(ej!)} = −ℑm{X(e−j!)} |X(ej!)| = |X(e−j!)| <)X(ej!) = −<)X(e−j!) Symmetry for Real, Even Signals x[n] real and even X(ej!) real and even Symmetry for Real, Odd Signals x[n] real and odd X(ej!) purely imaginary and odd Even-odd Decomposition of Real Signals xe[n] = Ev{x[n]} [x[n] real] xo[n] = Od{x[n]} [x[n] real] ℜe{X(ej!)} jℑm{X(ej!)} Parseval’s Relation for Aperiodic Signals +∞ X n=−∞ |x[n]|2 = 1 2 Z2 |X(ej!)|2d! Table 6: Basic Discrete-Time Fourier Transform Pairs Fourier series coefficients Signal Fourier transform (if periodic) X k=hNi akejk(2/N)n 2 +∞X k=−∞ ak ! − 2k N ak ej!0n 2 +∞X l=−∞ (! − !0 − 2l) (a) !0 = 2m N ak = 1, k = m,m ± N,m ± 2N, . . . 0, otherwise (b) !0 2 irrational ⇒ The signal is aperiodic cos !0n +∞X l=−∞ {(! − !0 − 2l) + (! + !0 − 2l)} (a) !0 = 2m N ak = 1 2 , k = ±m,±m ± N,±m ± 2N, . . . 0, otherwise (b) !0 2 irrational ⇒ The signal is aperiodic sin !0n
j +∞X l=−∞ {(! − !0 − 2l) − (! + !0 − 2l)} (a) !0 = 2r N ak = 1 2j , k = r, r ± N, r ± 2N, . . . − 1 2j , k = −r,−r ± N,−r ± 2N, . . . 0, otherwise (b) !0 2 irrational ⇒ The signal is aperiodic x[n] = 1 2 +∞X l=−∞ (! − 2l) ak = 1, k = 0,±N,±2N, . . . 0, otherwise Periodic square wave x[n] = 1, |n| ≤ N1 0, N1 < |n| ≤ N/2 and x[n + N] = x[n] 2 +∞X k=−∞ ak ! − 2k N ak = sin[(2k/N)(N1+1 2 )] N sin[2k/2N] , k 6= 0,±N,±2N, . . . ak = 2N1+1 N , k = 0,±N,±2N, . . . +∞X k=−∞ [n − kN] 2 N +∞X k=−∞ ! − 2k N ak = 1 N for all k anu[n], |a| < 1 1 1 − ae−j! — x[n] 1, |n| ≤ N1 0, |n| > N1 sin[!(N1 + 1 2 )] sin(!/2) — sinWn n = W sinc Wn 0 < W < X(ej!) = 1, 0 ≤ |!| ≤ W 0, W < |!| ≤ X(ej!)periodic with period 2 — [n] 1 — u[n] 1 1 − e−j! + +∞X k=−∞ (! − 2k) — [n − n0] e−j!n0 — (n + 1)anu[n], |a| < 1 1 (1 − ae−j!)2 — (n + r − 1)! n!(r − 1)! anu[n], |a| < 1 1 (1 − ae−j!)r — Table 7: Properties of the Laplace Transform Property Signal Transform ROC x(t) X(s) R x1(t) X1(s) R1 x2(t) X2(s) R2 Linearity ax1(t) + bx2(t) aX1(s) + bX2(s) At least R1 ∩ R2 Time shifting x(t − t0) e−st0X(s) R Shifting in the s-Domain es0tx(t) X(s − s0) Shifted version of R [i.e., s is in the ROC if (s − s0) is in R] Time scaling x(at) 1 |a| X s a “Scaled” ROC (i.e., s is in the ROC if (s/a) is in R) Conjugation x∗(t) X∗(s∗) R Convolution x1(t) ∗ x2(t) X1(s)X2(s) At least R1 ∩ R2 Differentiation in the Time Domain d dt x(t) sX(s) At least R Differentiation in the s-Domain −tx(t) d ds X(s) R Integration in the Time Domain Z t −∞ x( )d( ) 1 s X(s) At least R ∩ {ℜe{s} > 0} Initial- and Final Value Theorems If x(t) = 0 for t < 0 and x(t) contains no impulses or higher-order singularities at t = 0, then x(0+) = lims→∞ sX(s) If x(t) = 0 for t < 0 and x(t) has a finite limit as t → ∞, then limt→∞ x(t) = lims→0 sX(s) Table 8: Laplace Transforms of Elementary Functions Signal Transform ROC 1. (t) 1 All s 2. u(t) 1 s ℜe{s} > 0 3. −u(−t) 1 s ℜe{s} < 0 4. tn−1 (n − 1)! u(t) 1 sn ℜe{s} > 0 5. − tn−1 (n − 1)! u(−t) 1 sn ℜe{s} < 0 6. e−tu(t) 1 s + ℜe{s} > −ℜe{} 7. −e−tu(−t) 1 s + ℜe{s} < −ℜe{} 8. tn−1 (n − 1)! e−tu(t) 1 (s + )n ℜe{s} > −ℜe{} 9. − tn−1 (n − 1)! e−tu(−t) 1 (s + )n ℜe{s} < −ℜe{} 10. (t − T) e−sT All s 11. [cos !0t]u(t) s s2 + !2 0 ℜe{s} > 0 12. [sin !0t]u(t) !0 s2 + !2 0 ℜe{s} > 0 13. [e−t cos !0t]u(t) s + (s + )2 + !2 0 ℜe{s} > −ℜe{} 14. [e−t sin !0t]u(t) !0 (s + )2 + !2 0 ℜe{s} > −ℜe{} 15. un(t) = dn(t) dtn sn All s 16. u−n(t) = u(t) ∗ · · · ∗ u(t) | {z } n times 1 sn ℜe{s} > 0 Table 9: Properties of the z-Transform Property Sequence Transform ROC x[n] X(z) R x1[n] X1(z) R1 x2[n] X2(z) R2 Linearity ax1[n] + bx2[n] aX1(z) + bX2(z) At least the intersection of R1 and R2 Time shifting x[n − n0] z−n0X(z) R except for the possible addition or deletion of the origin Scaling in the ej!0nx[n] X(e−j!0z) R z-Domain zn 0 x[n] X z z0 z0R anx[n] X(a−1z) Scaled version of R (i.e., |a|R = the set of points {|a|z} for z in R) Time reversal x[−n] X(z−1) Inverted R (i.e., R−1 = the set of points z−1 where z is in R) Time expansion x(k)[n] = x[r], n = rk 0, n 6= rk X(zk) R1/k for some integer r (i.e., the set of points z1/k where z is in R) Conjugation x∗[n] X∗(z∗) R Convolution x1[n] ∗ x2[n] X1(z)X2(z) At least the intersection of R1 and R2 First difference x[n] − x[n − 1] (1 − z−1)X(z) At least the intersection of R and |z| > 0 Accumulation Pn k=−∞ x[k] 1 1−z−1X(z) At least the intersection of R and |z| > 1 Differentiation nx[n] −z dX(z) dz R in the z-Domain Initial Value Theorem If x[n] = 0 for n < 0, then x[0] = limz→∞ X(z) Table 10: Some Common z-Transform Pairs Signal Transform ROC 1. [n] 1 All z 2. u[n] 1 1−z−1 |z| > 1 3. u[−n − 1] 1 1−z−1 |z| < 1 4. [n − m] z−m All z except 0 (if m > 0) or ∞ (if m < 0) 5. nu[n] 1 1−z−1 |z| > || 6. −nu[−n − 1] 1 1−z−1 |z| < || 7. nnu[n] z−1 (1−z−1)2 |z| > || 8. −nnu[−n − 1] z−1 (1−z−1)2 |z| < || 9. [cos !0n]u[n] 1−[cos !0]z−1 1−[2 cos !0]z−1+z−2 |z| > 1 10. [sin !0n]u[n] [sin !0]z−1 1−[2 cos !0]z−1+z−2 |z| > 1 11. [rn cos !0n]u[n] 1−[r cos !0]z−1 1−[2r cos !0]z−1+r2z−2 |z| > r 12. [rn sin !0n]u[n] [r sin !0]z−1 1−[2r cos !0]z−1+r2z−2 |z| > r
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