transfer function op amp feedback circuit

Does anyone know how to calculate the transfer function for this circuit if Vref is the input an Vo the output? Thank you

• What are you taking as the input? Jun 3, 2015 at 1:31
• Thanks for the interest. Vref is the input, Vo is the output. Jun 3, 2015 at 1:53
• Are we assuming an ideal op-amp? Jun 3, 2015 at 2:16
• Yes ideal op amp Jun 3, 2015 at 2:28
• Use superposition: [Vref(1+Z2/Z1)+Vout*(-Z2/Z1)]*G=Vout Jun 3, 2015 at 3:02

The transfer function of such a system with feedback can be found using the general formula

Vout/Vin=H(forward)/(1-loop gain).

In you case:

Vout/Vref=G(s)(1+Z2/Z1)/[1-G(s)(-Z2/Z1)*H(s)]

If H(s) is not existent set H(s)=1.

• Thank you, what do you mean exactly with H(forward)? in your formula: Vout/Vin=H(forward)/(1-loop gain). Jun 3, 2015 at 8:43
• As you can see from the final transfer function formula, H(forward) is the forward gain between input and output without any feedback.
– LvW
Jun 3, 2015 at 11:46
• ok thx, it makes sense Jun 3, 2015 at 21:40