Does anyone know how to calculate the transfer function for this circuit if Vref is the input an Vo the output? Thank you 
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\$\begingroup\$ What are you taking as the input? \$\endgroup\$– The PhotonCommented Jun 3, 2015 at 1:31
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\$\begingroup\$ Thanks for the interest. Vref is the input, Vo is the output. \$\endgroup\$– LelloCommented Jun 3, 2015 at 1:53
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1\$\begingroup\$ Are we assuming an ideal op-amp? \$\endgroup\$– John DCommented Jun 3, 2015 at 2:16
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\$\begingroup\$ Yes ideal op amp \$\endgroup\$– LelloCommented Jun 3, 2015 at 2:28
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1\$\begingroup\$ Use superposition: [Vref(1+Z2/Z1)+Vout*(-Z2/Z1)]*G=Vout \$\endgroup\$– John DCommented Jun 3, 2015 at 3:02
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1 Answer
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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.
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\$\begingroup\$ Thank you, what do you mean exactly with H(forward)? in your formula: Vout/Vin=H(forward)/(1-loop gain). \$\endgroup\$– LelloCommented Jun 3, 2015 at 8:43
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\$\begingroup\$ As you can see from the final transfer function formula, H(forward) is the forward gain between input and output without any feedback. \$\endgroup\$– LvWCommented Jun 3, 2015 at 11:46
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