To find Cut-off frequency for a Low Pass Circuit

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#1 21672646 27 Oct 2014 20:51

Ansuman Hota Ansuman Hota

Anonymous

Post #1
21672646 27 Oct 2014 20:51

to find the cut off frequency of a low pass ckt having a combination of opamp and resistors?
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#2 21672647 27 Oct 2014 22:41

Nikki Martinez Nikki Martinez

Anonymous

Post #2
21672647 27 Oct 2014 22:41

Hi Ansuman. I think you can use the formula for cut-off frequency: fc= 1/2πfC
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#3 21672648 27 Oct 2014 23:43

Richard Gabric Richard Gabric

Anonymous

Post #3
21672648 27 Oct 2014 23:43

The simplest way is to plug the schematic into spice, which will give you the information you need quite rapidly.
To work out the transfer function analytically is quite time consuming, and probably best avoided, unless the question is related to a course of study.
You can't treat it simply as two cascaded RC sections, since feedback from the op amp significantly changes the behaviour.
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#4 21672649 28 Oct 2014 06:48

Ansuman Hota Ansuman Hota

Anonymous

Post #4
21672649 28 Oct 2014 06:48

thank you for replying but I dont understand how to solve this circuit , if i can get a little details then it would help me a lot ,as i'm preparing for some exams.
#5 21672650 28 Oct 2014 13:37

Richard Gabric Richard Gabric

Anonymous

Post #5
21672650 28 Oct 2014 13:37

The filter architecture is a Sallen-Key. There are many articles, with a full analysis of the transfer function available on the web. Try http://www.vyssotski.ch/BasicsOfInstrumentation/AnalysisOfTheSallen-KeyArchitecture.pdf for starters. If you are heading towards an exam, you will need to do more than just copy the article, work through it yourself from first principles and compare answers.
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To find Cut-off frequency for a Low Pass Circuit

To find Cut-off frequency for a Low Pass Circuit

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