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Is this how the lowpass butterworth analog filter can be implemented?

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  • $\begingroup$ sure, but you might need to know the values of $L_1$, $C_2$, $L_3$, and $R_4$ to get a 3rd-order butterworth LPF at with corner frequency, $f_0$, that is specified in advance. $\endgroup$ – robert bristow-johnson Dec 28 '14 at 21:14
  • $\begingroup$ Ok. Thanks, but is there a circuit to implement the 4th order analog lowpass butterworth filter? $\endgroup$ – ammar Dec 28 '14 at 21:23
  • $\begingroup$ you will need 4 reactive elements to get to 4th-order. perhaps another capacitor in parallel with the load resistor might do it. $\endgroup$ – robert bristow-johnson Dec 28 '14 at 21:50
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Yes but there are a lot of details; like merging R4 with a termination impedance and using pre-distortion to compensate for finite Q in the inductors. I would suggest reading some wikipedia articles: https://en.wikipedia.org/wiki/Analogue_filter https://en.wikipedia.org/wiki/Network_synthesis_filters https://en.wikipedia.org/wiki/Butterworth_filter https://en.wikipedia.org/wiki/Electronic_filter_topology#Ladder_topologies To get a feel for you want. Then you can decide how far you want to go along this path. Whether to learn how to do it yourself or find some prepacked program. But, unless you feel lucky today, proceed with caution and some knowledge. There are a lot of in's and out's; pitfalls. I have always found the field fascinating; but that's partially because it is complicated and fundamentally mathematical :) Your mileage will vary. BTW: this is a DSP forum not an analogue design forum.

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  • $\begingroup$ It's for both digital and analog signal processing, but circuit implementations should probably be on electronics.SE $\endgroup$ – endolith Dec 30 '14 at 19:48

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