Dear members of All About Circuits,

I am back to disturb you for a question I am stuck with.

I am asked to sketch a Bode Plot (magnitude only), for the circuit in the picture, showing the frequencies where the midband gain has fallen by 3dB.

I see that there are both a LPF and an HPF, so the first formula that comes into my mind is omega=1/RC. The problem is how to "relate" it to the op amp, can anyone help me?

Thanks in advance

All the best

 

You will firstly have to derive the transfer function relating the output voltage to the input voltage. If you can do this in the Laplace Transform domain it will make your job that much easier to then create the Bode plot.

 

Dear t_n_k,
first of all thanks for your reply.

One thing I don't get, though, is that in all the examples I have seen so far, the negative input of the Op Amp had the voltage source, whereas the positive input was grounded.

How does this affect the transfer function?

My idea was to work it out with something similar to the picture I am attaching, would that be ok?

Thank you so much!

 

The voltage gain for non inverter amplifier is equal to
Av = 1 + Z2/Z1
So the transfer function will look different.

 

Thanks Jony.

z2 is the feedback (1.5n || 9k) and z1 the "ground" (1k + 1u), isn't it?

Thank you!

 

z2 is the feedback (1.5n || 9k) and z1 the "ground" (1k + 1u), isn't it?

Yes, you got that part right.