Transfer function of an OP amp circuit.

TimeToShine

I have to find the transfer function H(w) = V0(w) / Vin(w) of a circuit which looks similar to the following:

http://i.imgur.com/LjCnt.jpg

I know that since the OP amp is infinite gain and ideal no current flows into the terminals, meaning that:

Ic = IR1 = IR2

I've let the impedance of C and R1 be R1 + 1/jwC, and R2 be R2.

How do I find the transfer function given these values? And how do i determine gain in dB as w tends to infinity if i'm given values when I have no gain A?

Michael Collins

Just find Vo in terms of Vin, using the rules you've already mentioned and the fact that the voltage at both op-amp inputs is equal. You'll see it's fairly easy.

The transfer function then is just Vo(jw)/Vin(jw) as I'm sure you know.

pljudge321

Maybe do your own circuits assignment instead of relying on people here.

TimeToShine

pljudge321 wrote: »

Maybe do your own circuits assignment instead of relying on people here.

it was just a question, relax. i didn't ask anyone to "do" it for me.

FarmerGreen

Assume the gain of the op-amp, open loop is say a 100 thousand, give or take a few thousand.
With feedback you can define this to say times ten or times fifty.
With great accuracy.
It doesnt really matter that much what the gain of the amp is, as long as its a lot and you dont ask too much from it.
There are frequency limitations, say if you were try and use an audio type at 50 Mhz then it wouldnt matter that much if it was in the circuit or not.

.........Oh.
You've just been suckered,TimeToShine
The hint is cnt.jpg

Bastards.
Me too, I can be hoaxed into crap so easily.
So lets take the piss out of it.

You gotta understand the problem before you find the the solution.
Otherwise you end up with Concorde or the Space Shuttle.

Ahem, looking at the circuit diagram we see that the generator has a + at the top and a - at the bottom.
So its a DC source, and rather luckily its decoupled with a capacitor so we dont need to worry about that any more.
I'm assuming its supposed to be a rail to rail IC, but it doesnt have a +ve supply does it?.

I'm not sure if this kind of crap is helpful when youre starting out, but you will damned lucky if you can put you feet up at the end of it and not say 'Oh Christ I Cant Believe I Did That'

Good luck with it.

JohnnyTodd

pljudge321 wrote: »

Maybe do your own circuits assignment instead of relying on people here.

Wow!

Guess I better not post my Analog questions in here

Michael Collins

JohnnyTodd wrote: »

Wow!

Guess I better not post my Analog questions in here

Feel free, once you're not looking for someone else to do an exam question for you. TimeToShine's question seems like it came straight from a past paper and he didn't show much engagement with it himself.

pljudge321

Michael Collins wrote: »

Feel free, once you're not looking for someone else to do an exam question for you. TimeToShine's question seems like it came straight from a past paper and he didn't show much engagement with it himself.

Exactly, I'm more than willing to help people who have problems with a concept and give them a nudge in the right direction. Circuits take practice which means solving them yourself, not copying down the answer and hoping the lecturer doesn't throw a curve ball in the exam.

JohnnyTodd

pljudge321 wrote: »

Exactly, I'm more than willing to help people who have problems with a concept and give them a nudge in the right direction. Circuits take practice which means solving them yourself, not copying down the answer and hoping the lecturer doesn't throw a curve ball in the exam.

It's an OP amp lads. Get over yourselves.