# op-amp transfer function help

Discussion in 'Homework Help' started by krl003, Jan 30, 2012.

1. ### krl003 Thread Starter New Member

Jan 30, 2012
7
0
Here is the circuit

Here are the equations I have so far:

Are these correct? The first two are obtained from voltage divider and the third one is obtained using KCL at the node between R1 and R2, V1. If these are correct, I'm having a hard time figuring out how to solve for Vo/Vi in the algebra...

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783

Do you mean after making the substitution for V1 [second equation] into the third equation you are struggling with simplifying the algebraic equation?

It might ease the burden somewhat if you recognize that

$V_o-V_1=V_o-V_o(1+j\omega R_2C_2)=-j\omega R_2C_2V_o$

3. ### krl003 Thread Starter New Member

Jan 30, 2012
7
0
I found my mistake, I forgot to multiply the Vo into the jwR2C2 term when simplifying that part of the equation.

Another question asks to find the input and output impedance as a function of radial frequency. But since it is an ideal op-amp, wouldn't the input be infinite and output be zero? What would the Bode Plot for these look like?

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Notwithstanding the op-amp is ideal, you would consider the input impedance (say) when connecting a signal at location Vin. Some current will be drawn into R1 from the signal source, so there will be a finite input impedance which is frequency dependent.