It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. I'm trying to design second order multiple feedback low-pass filter with cut-off frequency at Hz and Chebyshev approximation. However using Matlab and cheby1 function I get extremely high values of coefficients and as a result high values of resistors and capacitors.
I believe I know what the problem is: given equations are in normalized form and I need coefficients for normalized form too. Therefore as I understand I have to remove w from the equations but it has not helped me in some reason. Also I found normalized coefficients in my textbook:.
The last column is normalized coefficients for 2d order 3dB Chebyshev filter. But I can't understand where from I have to take H0. I am afraid that your transfer function is not correct. Your error can be verified very easily: All three expressions in the denominator must have the unit "1" - and this is not the case with your function.
The above two equations result from a comparison between the corrected! First, I will present a method that uses Mathematica to solve this problem. When I was studying this stuff I used the method all the time without using Mathematica of course. Well, we are trying to analyze the following opamp-circuit :. When we use and apply KCL , we can write the following set of equations:. When we use and apply Ohm's law , we can write the following set of equations:.
Now, using an ideal opamp , we know that:. My equation was also confirmed using LTspice. So, we get:. In order to make it a bit easier we assume a few things:. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?
Learn more. Multiple feedback low-pass filter design Ask Question. Asked 5 years ago. Active 2 months ago. Viewed 2k times. Transfer function for this scheme is defined as: Where: And condition for real values of resistors: However using Matlab and cheby1 function I get extremely high values of coefficients and as a result high values of resistors and capacitors.
What am I doing wrong? Also I found normalized coefficients in my textbook: The last column is normalized coefficients for 2d order 3dB Chebyshev filter. Long Smith. Long Smith Long Smith 1 1 silver badge 8 8 bronze badges.
This utility written in Javascript shall help you to quickly design and dimension your active Sallen-Key or Multiple Feedback topology low-pass filter. Enter the desired filter parameters and find the resulting circuit diagrams and component values below. In this utility great importance is attached to the possibility of automatic selection of capacitors out of the E6- or Eseries. New: If your filter is odd ordered i.
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