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Design >> Analog Design >> Intuitively find poles and zeros in a RC circuit
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Message started by curious on Nov 3^rd, 2017, 6:19pm

Title: Intuitively find poles and zeros in a RC circuit
Post by curious on Nov 3^rd, 2017, 6:19pm

I am reaching out to you to ask for some technical help. The question is how do we find poles and zeros in a circuit intuitively in the RC circuits without doing any mathematical calculations. This is something I am not good at and would like to learn. RC circuits by themselves or RC with Opamp. I would greatly appreciate if you can help me on this. Thank you very much in advance. http://www.swarthmore.edu/NatSci/echeeve1/Ref/FilterBkgrnd/Filters.html for example if we can discuss the simple bandpass with opamp in the link

Title: Re: Intuitively find poles and zeros in a RC circuit
Post by Ken Kundert on Nov 4^th, 2017, 9:58am

I recommend taking a look at Introduction to Phasors.

-Ken

Title: Re: Intuitively find poles and zeros in a RC circuit
Post by curious on Nov 4^th, 2017, 5:45pm

Hi Ken,

Thank you for referring me to the Phasors document. I understood the document and now trying to relate it to intuitively finding poles and zeros. In the last example of active filter (I think there is a typo in the diagram, shouldn't it be connected to the negative terminal), I can see there is a dominant pole from RfCf and now trying to figure out where is the other pole and zero coming from looking at the phasor diagram. Again I can derive mathematically. Also if one does not give any values to the components and ask for poles and zeros how do I do it (I am under the assumption that for Phasor analysis component values should be known)

If you can drive me through this one example step by step that would be of great help.
Thanks

Title: Re: Intuitively find poles and zeros in a RC circuit
Post by Ken Kundert on Nov 7^th, 2017, 12:06am

The other pole and zero come from Z_i. Remember that the input components that make up Z_i are completely isolated from the feedback components that make up Z_f by the opamp's virtual ground. Z_i ends up in the denominator of the overall transfer function, and so the pole and zero in Z_i become a zero and pole in the overall transfer function.

-Ken

Title: Re: Intuitively find poles and zeros in a RC circuit
Post by curious on Nov 8^th, 2017, 4:06am

Hi Ken,

Thank you. I also found this document during my search, attached to the message. I found it helpful as well.

Curious

Title: Re: Intuitively find poles and zeros in a RC circuit
Post by Frank_Heart on Nov 17^th, 2017, 10:53pm

also check Elmore delay which might be useful to you. -Frank