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Unformatted text preview: 1 1 Summary of Lecture #28 10/30/09 • Analog filters • Realization of LP filters, examples • Transformation from LP to HP, BP and BR • Frequency and magnitude scalingT • Examples • Additional remarks on SallenKey circuit • An example of active BP filters • Transformation from LP filters to HP filters • An example of RLC HP filters • See me before next Friday, Nov. 6, 2009 • if your test 2 score is less than 25. 2 Low pass filters • Ideal specification of low pass filters – Brick wall specification – H(j ϖ ) = 1 for ϖ ϖϖ < ϖ p – H(j ϖ ) = 0 for ϖ ϖϖ > ϖ p • Realization or approximation – Butterworth low pass transfer characteristic (maximum flat in pass band) – Chebyshev low pass transfer characteristic (equal ripples in pass band) – Inverse Chebyshev low pass transfer characteristic (equal ripples in stop band) – Elliptic low pass transfer characteristic – (equal ripples in pass and stop bands) • Prototype circuit with ϖ p = 1 rad/s, rate of roll off and 1 ohm impedance level • Frequency and magnitude scaling • 2 examples, by coefficient matching H(j ϖ ) 1 ϖ p ϖ 3 Max. flat in pass band Equal ripples in pass band Equal ripples in stop band Equal ripples in pass and stop bands H’, H”, H’” … are 0 dB at ϖ = 0. 4 Ex. 2. Design a LP filters with ϖ p = 218.7 π rad/s , a roll off rate of 60 dB/dec . and for a 100 Ω load. 60 dB/dec. → third order filter By applying KCL to nodes 1 and 2, we obtain 2 1 2 1 2 1 2 2 1 3 2 1 C LC 2 s C LC C C L s ) C 1 C 1 ( s ) C LC /( 1 ) s ( H + + + + + + = 5 2 1 2 1 2 1 2 2 1 3 2 1 C LC 2 s C LC C C L s ) C 1 C 1 ( s ) C LC /( 1 ) s ( H + + + + + +...
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This document was uploaded on 02/18/2010.
 Fall '06

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