problem with butterworth filter?

Question

problem with butterworth filter?

Answer 1

The op amp enables you to synthesize lively aspects like L and C that are too intense to be actual. huge inductances and capacitances, and subsequently make a filter out that does no longer be in any respect useful to construct employing unquestionably catalog instruments. i in my view can no longer do the synthesis, yet count on a instruction manual again up with the designs. that's the "instruction manual of lively filter out layout", by potential of Hilburn and Johnson, McGraw-Hill. A cookbook. All diagrams and charts, no heavy math. Butterworths and Chebyshev. For the dressmaker that merely desires a layout that works and could no longer get homework factors for synthesis, that's a sturdy e book and its designs have labored for me. i prefer to propose it.

Answer 2

A 4th order lowpass filter has a -80 db/decade roll off. Do you want a roll off of -5 db/dec or -50db/dec? -5 doesn't make sense. Do you need a passband gain of exactly 4.0? If you use a Sallen-Key configuration, the filter will have a passband gain of 4.0 if each resistive feedback network has a feedback ratio of .5, in other words, 2 resistors of equal value for each stage, but the filter may not be configurable as a Butterworth to get this gain. The filter poles for Butterworth are to be placed at uniform angle separation on a semicircle in the left half-plane of the s-domain, or 45 degrees apart, for 4-pole. The 2 conjugate poles closest to the jw axis are 22.5 degrees displaced from this axis. The problem is this: getting the exact gain that you want influences placing the poles where you want them on this semicircle, so I'm not sure you can properly place the poles being constrained by a gain of 4 and the Sallen-Key topology. The angle that a pair of complex poles makes with the real axis is influenced by the passband gain of the Sallen-Key topology. I must say the design of these filters is a challenge for beginners. It really is almost a requirement that you completely understand the canonical 2nd order system function, every term and parameter in this function AND how each relates to pole location, AND how pole location affects system behavior. Try this tutorial on Sallen-Key filter design: http://web2.clarkson.edu/class/ee311/Experiment3/Lab3_F06.PDF

That being said, we experienced engineers are spending time on these questions and would be impressed with proper spelling, capitalization, punctuation and grammer from the questioners.

Answer 3

Not making any sense. A 4th order Butterworth filter has an attenuation of 24 dB/octave = 80 dB/decade outside the passband. So what's 5 dB/decade got to do with anything? A single reactive pole can only give 6 dB/octave = 20 dB/dcade. A 4th order Butterworth non-unity gain filter has a first stage voltage gain of about 1.15 and a second stage voltage gain of about 2.24 for a total circuit voltage gain of about 2.6. Because the gain directly affects the damping, changing the gain changes the damping which makes the filter no longer a Butterworth.