# Transfer function of an op amp

Discussion in 'Homework Help' started by Geotraker, Feb 24, 2014.

1. ### Geotraker Thread Starter New Member

May 9, 2013
2
0
How to find the transfer function (or the gain) of the following circuit?
Can we short circuit R2 since there cannot be any input current?

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2. ### t06afre AAC Fanatic!

May 11, 2009
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If this is an ideal opamp no current will flow in R2 so I would say yes. However are you sure you have drawn this correct. As your drawing looks very simlar to a Sallen and Key filter section
http://www.ti.com/lit/an/sloa024b/sloa024b.pdf

3. ### LvW Active Member

Jun 13, 2013
674
100
Yes - I agree with t06afre.
However, in case of a true Sallen-Key lowpass (with C2 shifted to the non-inv. opamp input) the resistor R2, of course, must NOT be cancelled.

4. ### Geotraker Thread Starter New Member

May 9, 2013
2
0
Thank you all. The schematic was wrong. Here is the correct one and I was able to solve that.

Solving procedure,
Apply KCL at V1
Apply KCL at V2
Remove V1 from above two equations and find V2-----(A)
Apply KCL at V3 and find V3----(B)
Apply Golden rules V2=V3
Make (A)=(B) and find (Vout/Vin) ratio from it.

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5. ### LvW Active Member

Jun 13, 2013
674
100
Fine - that`s exactly the way I would solve the problem.