# Op Amp Analysis Question

## Homework Statement

G'day, the op-amp circuit is attached. Need to know the Transfer Function.

## Homework Equations

Using Ideal analysis. In=Ip=0A, and Vn=Vp
Vo/Vi=-15

## The Attempt at a Solution

I have had many attempts at it. Because We don't know the input current (no input resister) it has stumped me. As there is no point doin KCL at the first left node. I have many equations but they don't seem to link up. Obviously V1=0V. V2=(2/10)Vo. and Va/18k=-Vi/6k.
Any help greatly appreciated.

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The Electrician
Gold Member
Assume the opamps are ideal: infinite gain, zero output impedance, zero input current.

Then the 75K resistor does nothing. Vi is driven by a voltage source, so the 75K doesn't load it, and has no effect on the current into the 6K resistor. The output of the second opamp has zero ohms impedance, so whatever current goes from Vi to Vo via the 75K has no effect on the output voltage.

So all you have is an inverting amplifier followed by a non-inverting amplifier. Calculate the gains of each and multiply them and that's your transfer function.

If the assumption about opamp ideality isn't true, then things get more complicated.

thanks

cheers