Line 26: Line 26:
 
& = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\
 
& = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\
 
& \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j},  a_k = 0 \text{ for all other k} \\
 
& \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j},  a_k = 0 \text{ for all other k} \\
2) x(t) = 2 + cos(6 \pi t) - \frac{1}{2} sin(3 \pi t), \omega_{o} = 3\pi \\
+
\text{2) } x(t) = 2 + cos(6 \pi t) - \frac{1}{2} sin(3 \pi t), \omega_{o} = 3\pi \\
 
& = 2 + \frac{1}{2}(e^{j6\pi t} + e^{-j6\pi t}) + \frac{1}{4j} (e^{j3\pi t} -e^{-j3\pi t}) \\
 
& = 2 + \frac{1}{2}(e^{j6\pi t} + e^{-j6\pi t}) + \frac{1}{4j} (e^{j3\pi t} -e^{-j3\pi t}) \\
 
& \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\
 
& \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\
Line 32: Line 32:
 
& = 2e^{j \omega_o (0)t} +  \frac{1}{2}e^{j \omega_o (2)t} +  \frac{1}{2}e^{j \omega_o (-2)t} +  \frac{1}{4j}e^{j \omega_o (1)t} -  \frac{1}{4j}e^{j \omega_o (-1)t} \\\
 
& = 2e^{j \omega_o (0)t} +  \frac{1}{2}e^{j \omega_o (2)t} +  \frac{1}{2}e^{j \omega_o (-2)t} +  \frac{1}{4j}e^{j \omega_o (1)t} -  \frac{1}{4j}e^{j \omega_o (-1)t} \\\
 
& \text{So we can say that } a_0 = 2,  a_1 = \frac{1}{4j}, a_{-1} = -\frac{1}{4j}, a_2 = a_{-2} = \frac{1}{2}, a_k = 0 \text{ for all other k} \\
 
& \text{So we can say that } a_0 = 2,  a_1 = \frac{1}{4j}, a_{-1} = -\frac{1}{4j}, a_2 = a_{-2} = \frac{1}{2}, a_k = 0 \text{ for all other k} \\
3) x(t) = cos(\frac{2\pi}{10}t), \omega_{o} = \frac{\pi}{10} \\
+
\text{3) } x(t) = cos(\frac{2\pi}{10}t), \omega_{o} = \frac{\pi}{10} \\
 
& = \frac{e^{j\frac{2\pi}{10} t} + e^{-j\frac{2\pi}{10} t} }{2} \\
 
& = \frac{e^{j\frac{2\pi}{10} t} + e^{-j\frac{2\pi}{10} t} }{2} \\
 
& = \frac{1}{2}e^{j\frac{2\pi}{10} t} + \frac{1}{2}e^{-j\frac{2\pi}{10} t}  \\
 
& = \frac{1}{2}e^{j\frac{2\pi}{10} t} + \frac{1}{2}e^{-j\frac{2\pi}{10} t}  \\
Line 39: Line 39:
 
& = \frac{1}{2}e^{j\omega_o(2) t} + \frac{1}{2}e^{-j\omega_o(-2) t}  \\
 
& = \frac{1}{2}e^{j\omega_o(2) t} + \frac{1}{2}e^{-j\omega_o(-2) t}  \\
 
& \text{So we can say that } a_2 = a_{-2} = \frac{1}{2},  a_k = 0 \text{ for all other k}\\
 
& \text{So we can say that } a_2 = a_{-2} = \frac{1}{2},  a_k = 0 \text{ for all other k}\\
4) x(t) =
+
\text{4) } x(t) =
 
  \begin{cases}
 
  \begin{cases}
 
   3, & \text{if}\ a=1 \\
 
   3, & \text{if}\ a=1 \\
Line 53: Line 53:
 
\begin{align}
 
\begin{align}
  
 
+
\text{1) } x[n] = sin(12 \pi n)
x[n] = 1 + sin(\frac{2\pi}{8}n) + 3cos(\frac{2\pi}{8}n), N=8 --> \omega_{o} = \frac{2\pi}{8} \\
+
& = \frac{e^{j6\pi t} - e^{-j6\pi t} }{2j} \\
x[n] = -j^n, \omega_o = \frac{\pi}{2} \\
+
& = \frac{1}{2j} e^{j6\pi t} - \frac{1}{2j} e^{-j6\pi t} \\
x[n] =
+
& \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\
 +
& \text{Here, } \omega_o = 6 \pi \text{ ,therefore, } \\
 +
& = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\
 +
& \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j},  a_k = 0 \text{ for all other k} \\
 +
\text{2) } x[n] = 1 + sin(\frac{2\pi}{8}n) + 3cos(\frac{2\pi}{8}n), N=8 --> \omega_{o} = \frac{2\pi}{8} \\
 +
& = \frac{e^{j6\pi t} - e^{-j6\pi t} }{2j} \\
 +
& = \frac{1}{2j} e^{j6\pi t} - \frac{1}{2j} e^{-j6\pi t} \\
 +
& \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\
 +
& \text{Here, } \omega_o = 6 \pi \text{ ,therefore, } \\
 +
& = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\
 +
& \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j},  a_k = 0 \text{ for all other k} \\
 +
\text{3) } x[n] = -j^n, \omega_o = \frac{\pi}{2} \\
 +
\text{4) } x[n] =
 
  \begin{cases}
 
  \begin{cases}
 
   sin(\pi t), & \text{if}\ a=1 \\
 
   sin(\pi t), & \text{if}\ a=1 \\
 
   0, & \text{otherwise}
 
   0, & \text{otherwise}
 
  \end{cases}\\
 
  \end{cases}\\
x[n] =
+
 
\begin{cases}
+
  4, & \text{if}\ a=1 \\
+
  -4, & \text{otherwise}
+
\end{cases}
+
  
 
\end{align}
 
\end{align}

Revision as of 14:39, 26 April 2019


Fourier Series Coefficients

A project by Kalyan Mada



Introduction

I am going to compute some fourier series coefficients.


CT signals

$ \begin{align} \text{1) } x(t) = sin(6 \pi t), \omega_{o} = 6\pi \\ & = \frac{e^{j6\pi t} - e^{-j6\pi t} }{2j} \\ & = \frac{1}{2j} e^{j6\pi t} - \frac{1}{2j} e^{-j6\pi t} \\ & \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\ & \text{Here, } \omega_o = 6 \pi \text{ ,therefore, } \\ & = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\ & \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j}, a_k = 0 \text{ for all other k} \\ \text{2) } x(t) = 2 + cos(6 \pi t) - \frac{1}{2} sin(3 \pi t), \omega_{o} = 3\pi \\ & = 2 + \frac{1}{2}(e^{j6\pi t} + e^{-j6\pi t}) + \frac{1}{4j} (e^{j3\pi t} -e^{-j3\pi t}) \\ & \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\ & \text{Here, } \omega_o = 3 \pi \text{ ,therefore, } \\ & = 2e^{j \omega_o (0)t} + \frac{1}{2}e^{j \omega_o (2)t} + \frac{1}{2}e^{j \omega_o (-2)t} + \frac{1}{4j}e^{j \omega_o (1)t} - \frac{1}{4j}e^{j \omega_o (-1)t} \\\ & \text{So we can say that } a_0 = 2, a_1 = \frac{1}{4j}, a_{-1} = -\frac{1}{4j}, a_2 = a_{-2} = \frac{1}{2}, a_k = 0 \text{ for all other k} \\ \text{3) } x(t) = cos(\frac{2\pi}{10}t), \omega_{o} = \frac{\pi}{10} \\ & = \frac{e^{j\frac{2\pi}{10} t} + e^{-j\frac{2\pi}{10} t} }{2} \\ & = \frac{1}{2}e^{j\frac{2\pi}{10} t} + \frac{1}{2}e^{-j\frac{2\pi}{10} t} \\ & \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\ & \text{Here, } \omega_o = \frac{ \pi}{10} \text{ ,therefore, } \\ & = \frac{1}{2}e^{j\omega_o(2) t} + \frac{1}{2}e^{-j\omega_o(-2) t} \\ & \text{So we can say that } a_2 = a_{-2} = \frac{1}{2}, a_k = 0 \text{ for all other k}\\ \text{4) } x(t) = \begin{cases} 3, & \text{if}\ a=1 \\ 0, & \text{otherwise} \end{cases} \end{align} $


DT signals

$ \begin{align} \text{1) } x[n] = sin(12 \pi n) & = \frac{e^{j6\pi t} - e^{-j6\pi t} }{2j} \\ & = \frac{1}{2j} e^{j6\pi t} - \frac{1}{2j} e^{-j6\pi t} \\ & \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\ & \text{Here, } \omega_o = 6 \pi \text{ ,therefore, } \\ & = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\ & \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j}, a_k = 0 \text{ for all other k} \\ \text{2) } x[n] = 1 + sin(\frac{2\pi}{8}n) + 3cos(\frac{2\pi}{8}n), N=8 --> \omega_{o} = \frac{2\pi}{8} \\ & = \frac{e^{j6\pi t} - e^{-j6\pi t} }{2j} \\ & = \frac{1}{2j} e^{j6\pi t} - \frac{1}{2j} e^{-j6\pi t} \\ & \text{By Fourier Series we know that} \sum_{k=-\infty}^\infty a_k e^{jk\omega_o t} \\ & \text{Here, } \omega_o = 6 \pi \text{ ,therefore, } \\ & = \frac{1}{2j} e^{j\omega_o(1) t} - \frac{1}{2j} e^{j\omega_o(-1) t} \\ & \text{So we can say that } a_1 = \frac{1}{2j}, a_{-1} = -\frac{1}{2j}, a_k = 0 \text{ for all other k} \\ \text{3) } x[n] = -j^n, \omega_o = \frac{\pi}{2} \\ \text{4) } x[n] = \begin{cases} sin(\pi t), & \text{if}\ a=1 \\ 0, & \text{otherwise} \end{cases}\\ \end{align} $



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[to 2019 Spring ECE 301 Boutin]


Alumni Liaison

Abstract algebra continues the conceptual developments of linear algebra, on an even grander scale.

Dr. Paul Garrett