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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 Photon
    Jun 3 '15 at 1:31
  • \$\begingroup\$ Thanks for the interest. Vref is the input, Vo is the output. \$\endgroup\$
    – Lello
    Jun 3 '15 at 1:53
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    \$\begingroup\$ Are we assuming an ideal op-amp? \$\endgroup\$
    – John D
    Jun 3 '15 at 2:16
  • \$\begingroup\$ Yes ideal op amp \$\endgroup\$
    – Lello
    Jun 3 '15 at 2:28
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    \$\begingroup\$ Use superposition: [Vref(1+Z2/Z1)+Vout*(-Z2/Z1)]*G=Vout \$\endgroup\$
    – John D
    Jun 3 '15 at 3:02
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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\$
    – Lello
    Jun 3 '15 at 8:43
  • \$\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\$
    – LvW
    Jun 3 '15 at 11:46
  • \$\begingroup\$ ok thx, it makes sense \$\endgroup\$
    – Lello
    Jun 3 '15 at 21:40

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