FILTERS

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FILTERS

• 09-27-07

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Basics of filter

• Definition passes or blocks certain frequencies
• Components used to design passive filters R, L,
  and C
• Purpose of filter
• Application
• Analysis and Design of filters

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Classification of filters

• Passive filters or Active filters
• Analog or Digital
• Linear or Non linear
• Passive filters subdivided to
• 1) Low pass filter attenuation above cut off
• 2) High pass filter attenuation below cut off
• 3) Band pass
• 4) Stop band/Notch filter

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Filter Analysis

• Bode plots are used to plot the response of the
  filters.
• Log magnitude of the transfer function is plotted
  against log frequency
• Example of Bode plot for low pass filter
• Define components cut off/corner frequency,
  Gain (decibels), Frequency (rad/sec) log scale
  and roll off rate

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Transfer Function

• Output, Input, LTI systems
• Poles and zeroes
• order

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• There is a phase angle vs. log frequency plot.
• Phase relationship of a output at given frequency
  compared to the input.

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System with zeroes and its bode plots
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Phase plot for zeroes in bode plot
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System with poles and its bode plot
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System with a combination of poles and zeroes
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Phase plot
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Frequency components

• Z Impedance is term used in AC circuit
• Impedance for resistor
• Impedance for inductor
• Impedance for capacitor and its representation in
  frequency domain by Laplace transform

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• Circuit for Low pass and high pass filters and
  its solution using the traditional method and
  method of transfer function

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• Ideal Filters and its characteristics
• Filter defined from cut off frequency and roll
  off rate
• Roll of rate and its change with number of poles
  in the circuit
• Trade off between ideal and real filters
• Order of the filter determined from the degree of
  the TF

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• Higher the order of the filter
• 1) closer to ideal behavior
• 2) More complex the circuit
• 3) determined by number of R, L and C in the
  circuit

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Filter response and its categorization

• 1) Butterworth filter
• 2)Chebyshev filter
• 3) Bessel filter

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Design of filter

• Use of look up table for finding the coefficients
  in the TF
• Higher order filters and its implementation from
  lower order filters
• Requirements and that decided number of
  components in the circuit

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• Thank You
• Questions