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| + | [[Category:problem solving]] | ||
| + | [[Category:ECE301]] | ||
| + | [[Category:ECE]] | ||
| + | [[Category:Fourier transform]] | ||
| + | [[Category:signals and systems]] | ||
| + | == Example of Computation of Fourier transform of a CT SIGNAL == | ||
| + | A [[CT_Fourier_transform_practice_problems_list|practice problem on CT Fourier transform]] | ||
| + | ---- | ||
| + | |||
==Fourier Transform== | ==Fourier Transform== | ||
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<font "size"=4> | <font "size"=4> | ||
| − | <math>x(t)=t^2 u(t)</math> | + | <math>x(t)=t^2 u(t-1)</math> |
</font> | </font> | ||
| − | <math>X(\omega)=\int_{-\infty}^{\infty}t^2 u(t) e^{-j\omega t}dt \; = \int_{ | + | <math>X(\omega)=\int_{-\infty}^{\infty}t^2 u(t-1) e^{-j\omega t}dt \; = \int_{1}^{\infty}t^2 e^{-j\omega t}dt</math> |
| Line 18: | Line 27: | ||
<math>du=2t \; dt \; \; \; \; \; \; \; \; v = \frac{1}{-j\omega}e^{-j \omega t}</math> | <math>du=2t \; dt \; \; \; \; \; \; \; \; v = \frac{1}{-j\omega}e^{-j \omega t}</math> | ||
| − | <math>X(\omega)=\frac{t^2 | + | <math>X(\omega)=\frac{t^2 j}{\omega}e^{-j\omega t}|_{1}^{\infty} + \frac{2}{j \omega}\int_{1}^{\infty}t^2 e^{-j\omega t}dt</math> |
| + | |||
| + | ''Integration by Parts'' | ||
| + | |||
| + | <math>u=t \; \; \; \; \; \; \; \; \; \; \; \; \; dv = e^{-j \omega t}</math> | ||
| + | |||
| + | <math>du=1 \; dt \; \; \; \; \; \; \; \; v = \frac{1}{-j\omega}e^{-j \omega t}</math> | ||
| + | |||
| + | <math>X(\omega)=\frac{t^2 j}{\omega}e^{-j\omega t}|_{1}^{\infty} + \frac{2}{j \omega}[\frac{tj}{\omega}e^{-j\omega t}|_{1}^{\infty}+\frac{1}{j \omega}\int_{1}^{\infty}e^{-j\omega t}dt]</math> | ||
| + | |||
| + | <math>=[\frac{t^2 j}{\omega}e^{-j\omega t} + \frac{2}{j \omega}(\frac{tj}{\omega}e^{-j\omega t}+\frac{1}{\omega ^2}e^{-j\omega t})]_{1}^{\infty}</math> | ||
| + | |||
| + | <math>=(0) - (jt^2 e^{-jt} + 2te^{-jt}+\frac{2}{j}e^{-jt})</math> | ||
| + | |||
| + | <font size="4.5"> | ||
| + | <math>=je^{-jt}(-t^2 + j2t + 2)</math> | ||
| + | </font> | ||
| + | |||
| + | ---- | ||
| + | [[CT_Fourier_transform_practice_problems_list|Back to Practice Problems on CT Fourier transform]] | ||
Latest revision as of 11:24, 16 September 2013
Example of Computation of Fourier transform of a CT SIGNAL
A practice problem on CT Fourier transform
Fourier Transform
$ X(\omega)=\int_{-\infty}^{\infty}x(t)e^{-j\omega t}dt $
$ x(t)=t^2 u(t-1) $
$ X(\omega)=\int_{-\infty}^{\infty}t^2 u(t-1) e^{-j\omega t}dt \; = \int_{1}^{\infty}t^2 e^{-j\omega t}dt $
Integration by Parts
$ \int u \; dv = uv - \int v \; du $
$ u=t^2 \; \; \; \; \; \; \; \; \; \; \; \; \; dv = e^{-j \omega t} $
$ du=2t \; dt \; \; \; \; \; \; \; \; v = \frac{1}{-j\omega}e^{-j \omega t} $
$ X(\omega)=\frac{t^2 j}{\omega}e^{-j\omega t}|_{1}^{\infty} + \frac{2}{j \omega}\int_{1}^{\infty}t^2 e^{-j\omega t}dt $
Integration by Parts
$ u=t \; \; \; \; \; \; \; \; \; \; \; \; \; dv = e^{-j \omega t} $
$ du=1 \; dt \; \; \; \; \; \; \; \; v = \frac{1}{-j\omega}e^{-j \omega t} $
$ X(\omega)=\frac{t^2 j}{\omega}e^{-j\omega t}|_{1}^{\infty} + \frac{2}{j \omega}[\frac{tj}{\omega}e^{-j\omega t}|_{1}^{\infty}+\frac{1}{j \omega}\int_{1}^{\infty}e^{-j\omega t}dt] $
$ =[\frac{t^2 j}{\omega}e^{-j\omega t} + \frac{2}{j \omega}(\frac{tj}{\omega}e^{-j\omega t}+\frac{1}{\omega ^2}e^{-j\omega t})]_{1}^{\infty} $
$ =(0) - (jt^2 e^{-jt} + 2te^{-jt}+\frac{2}{j}e^{-jt}) $
$ =je^{-jt}(-t^2 + j2t + 2) $
