Whenever I try this imported OpAmp to simulate a Sallen-key 2nd-order OpAmp filter in LTspice, it never reaches the DC operating point.

Is it the spice model or the components' value?

I want to upload the file but no way here.

enter image description here

  • 4
    \$\begingroup\$ V3 appears to have a DC voltage of 5 V, OK so then the DC biasing is such that there will be +5 V at the + input of the opamp. The opamp is in unity gain so there should be +5 V at the output as well. What is the opamp's supply voltage? It's +5 V and - 5 V. Hmm, that means there is no margin between the +5 V DC biasing point and the supply voltage. That will not work. Increase the supply voltage to +10 V and -10 V or make the DC voltage of V3 equal to 0 V. \$\endgroup\$ Mar 2, 2020 at 8:44
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    \$\begingroup\$ If you were to actually build this, the OPA388 will be damaged as the maximum supply voltage of the OPA388 is 6 V (or +3 V and - 3V), you're applying 10 V ! \$\endgroup\$ Mar 2, 2020 at 8:46
  • \$\begingroup\$ I made a stupid mistake. How can I make your answer as the right one? \$\endgroup\$
    – Yaakov
    Mar 2, 2020 at 9:18
  • 1
    \$\begingroup\$ @Yaakov You can write it up, yourself, and then select it. (May as well.) It doesn't appear that anyone else is trying to "take the spot." So you may as well provide your own answer. (It's allowed.) \$\endgroup\$
    – jonk
    Mar 3, 2020 at 2:11

1 Answer 1


THe DC bias should be 0V instead of 5V,as there rail to rail voltage value is +5V/-5V


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