(New page: == Example of a periodic CT signal == The following is a periodic signal: <math>\,x(t)=(1+j)cos(\pi t)+sin(2\pi t)</math> Using Eulers formula, we can interpret this function in terms of...) |
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| + | == Fourier sum definition == | ||
| + | The function as defined by summing fourier coefficients <math>\,a_k</math> is defined as: | ||
| + | |||
| + | <math>x(t)=\sum^{\infty}_{k=-\infty} a_k e^{jk\omega_0 t}\,</math> | ||
| + | |||
== Example of a periodic CT signal == | == Example of a periodic CT signal == | ||
| + | |||
The following is a periodic signal: | The following is a periodic signal: | ||
<math>\,x(t)=(1+j)cos(\pi t)+sin(2\pi t)</math> | <math>\,x(t)=(1+j)cos(\pi t)+sin(2\pi t)</math> | ||
| − | Using Eulers formula, we can interpret this function in terms of exponentials which can then be used to compute the <math>a_k</math> values for a Fourier series: | + | Using Eulers formula, we can interpret this function in terms of exponentials which can then be used to compute the <math>\,a_k</math> values for a Fourier series: |
<math>\,x(t)=(1+j)\frac {e^{j\pi t}+e^{-j \pi t}}{2} + \frac {e^{j2 \pi t}-e^{-j2 \pi t}}{2j}</math> | <math>\,x(t)=(1+j)\frac {e^{j\pi t}+e^{-j \pi t}}{2} + \frac {e^{j2 \pi t}-e^{-j2 \pi t}}{2j}</math> | ||
| + | Now splitting up: | ||
| + | |||
| + | <math>x(t)=\frac{1+j}{2}e^{j\pi t}+\frac{1+j}{2}e^{-j\pi t}+\frac{1+j}{2j}e^{j\pi t}+\frac{-1-j}{2j}e^{-j\pi t}</math> | ||
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| + | choose <math>\,\omega_0</math> as <math>\,\pi</math>, the smallest period between the two parts. | ||
| + | |||
| + | so this function becomes: | ||
| + | |||
| + | <math>x(t)=\sum^{\infty}_{k=-\infty} a_k e^{jk\pi t}\,</math> | ||
| + | |||
| + | Which very nearly matches our function, we only need solve or point out our <math>\,a_k</math> values. | ||
| + | |||
| + | <math>a_1=\frac{1+j}{2}</math> | ||
| + | |||
| + | <math>a_-1=\frac{1+j}{2}</math> | ||
| + | |||
| + | <math>a_2=\frac{1+j}{2j}</math> | ||
| + | <math>a_-2=\frac{-1-j}{2j}</math> | ||
| − | <math> | + | All other <math>\,a_k</math> values are zero. |
Revision as of 12:24, 25 September 2008
Fourier sum definition
The function as defined by summing fourier coefficients $ \,a_k $ is defined as:
$ x(t)=\sum^{\infty}_{k=-\infty} a_k e^{jk\omega_0 t}\, $
Example of a periodic CT signal
The following is a periodic signal:
$ \,x(t)=(1+j)cos(\pi t)+sin(2\pi t) $
Using Eulers formula, we can interpret this function in terms of exponentials which can then be used to compute the $ \,a_k $ values for a Fourier series:
$ \,x(t)=(1+j)\frac {e^{j\pi t}+e^{-j \pi t}}{2} + \frac {e^{j2 \pi t}-e^{-j2 \pi t}}{2j} $
Now splitting up:
$ x(t)=\frac{1+j}{2}e^{j\pi t}+\frac{1+j}{2}e^{-j\pi t}+\frac{1+j}{2j}e^{j\pi t}+\frac{-1-j}{2j}e^{-j\pi t} $
choose $ \,\omega_0 $ as $ \,\pi $, the smallest period between the two parts.
so this function becomes:
$ x(t)=\sum^{\infty}_{k=-\infty} a_k e^{jk\pi t}\, $
Which very nearly matches our function, we only need solve or point out our $ \,a_k $ values.
$ a_1=\frac{1+j}{2} $
$ a_-1=\frac{1+j}{2} $
$ a_2=\frac{1+j}{2j} $
$ a_-2=\frac{-1-j}{2j} $
All other $ \,a_k $ values are zero.
