Lecture 40_v2 - Lecture 40 Active filters Spring 2011 ECE...

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Spring 2011 ECE 2100, Cornell Univ, Prof. Molnar 1 Lecture 40 Active filters
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Spring 2011 ECE 2100, Cornell Univ, Prof. Molnar 2 Example filter design • To meet suppression spec over 2 octaves: get - 12dB/pole, – need 3 poles at 100kHz • If all three real: get -9dB at 100kHz: fails flatness • So need complex conjugate poles as well as real – Choose Q~1.4 to balance roll-off from real pole – This works… but how to implement? – And need gain -36dB 100kHz 400kHz Out-of band rejection In band flatness ( 29 60 , 4 . 1 , 100 2 2 2 2 = = = + + + = G Q kHz Q s s s G s H o o o o o o π ϖ
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Spring 2011 ECE 2100, Cornell Univ, Prof. Molnar 3 Multi-stage filters • In principal can connect multiple stages passively – But hard: stages interact – each loads the previous one – And no gain. • Can use op-amps to buffer stages+ provide gain – Each stage is isolated from the last – Avoids interactions H(s) is not LC RC s s LC RC s RC 1 1 1 1 2 + + + But this is:
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This note was uploaded on 06/10/2011 for the course ECE 2100 taught by Professor Kelley/seyler during the Spring '05 term at Cornell University (Engineering School).

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Lecture 40_v2 - Lecture 40 Active filters Spring 2011 ECE...

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