I need to find the transfer function of Sallen-Key second order notch filter.
Is there any program that can show the transfer function of s?
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\$\begingroup\$ Yes, there are both simulation programs like spice and algebraic approaches. \$\endgroup\$– Chris StrattonCommented May 1, 2013 at 17:37
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2 Answers
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answered May 1, 2013 at 18:06
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If you have reduced your filter to a circuit design with known R and C values, then LTSpice or any other SPICE-like simulator can give you transfer function. Simply apply an ac input, and measure the magnitude and phase of the output in an ac sweep.
If you have a set of poles and zeros, you could either reduce it to a circuit and use SPICE, or use any numerical analysis (for example, Matlab or Octave) or computer algebra (for example, Mathematica or Maxsyma) package to calculate the corresponding magnitude and phase response over frequency.
answered May 1, 2013 at 18:12
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\$\begingroup\$ How can i find the transfer function using LTSpice? I can't find out. Thanks in advance. \$\endgroup\$– KeyC0deCommented Sep 1, 2015 at 16:48
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\$\begingroup\$ @RestlessC0bra, apply an AC stimulus at the input. Do an AC simulation. Measure the signal at the output. Plot the ratio between the two (More conveniently, just make the stimulus with amplitude 1 and phase 0). \$\endgroup\$ Commented Sep 1, 2015 at 16:50
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\$\begingroup\$ Sorry, but i don't understand how this will give me the transfer function of a circuit. I want the transfer function complete given all the state variables of the circuit, like the Sallen-Key transfer function. Say i draw a LP Sallen Key on LTSpice. Then, can i go somewhere on the program that will give me explicitly the transfer function of this entire circuit? \$\endgroup\$– KeyC0deCommented Sep 1, 2015 at 17:22
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\$\begingroup\$ @RestlessC0bra Maybe you should ask a new question. But be sure to be clear what you're asking about. The usual meaning of "transfer function" is the ratio between the output and input signals (taken as phasors). \$\endgroup\$ Commented Sep 1, 2015 at 17:39