I want to replicate this structure in LTspice where the components 1, 3 et 4 are resistors with the same resistance R and 2 et 5 are two capacitors and opamp LT1356

this is the schema I made
this is the bode plot:
I think it's wrong because the max value of the gain is -50 dB while I need to find the frequency at -3 dB


1 Answer 1


Good intuition that something is wrong. As soon as you see weird things in the AC response, you need to head back to TRANsient or DC to figure out what's going on. However, I did spot two things:

enter image description here

  1. Your negative power supply is supplying +15V instead of -15V. Your circuit is basically unpowered as there is no voltage across the VDD/VSS pins of your op-amp. Either rotate V2 or make the value of V2 negative.
  2. Don't connect two wires directly to the pin of a schematic symbol - it's hard to read and your CAD system might not make one of the three connections you're expecting it to.
  • 1
    \$\begingroup\$ You nailed it. I just tried simulating his circuit in LTSpice, but with the V- negative rail actually negative, and the bode plot looks like just what one would expect: metacollin.com/s/jhJecCPy0Bcd.png Might be worth editing your answer to say that the negative rail is definitely the problem. Feel free to use the screenshot I linked in your answer if desired. \$\endgroup\$
    – metacollin
    Commented Jun 15, 2020 at 18:40
  • \$\begingroup\$ Thank you very much \$\endgroup\$
    – Salah Ar
    Commented Jun 15, 2020 at 18:43
  • \$\begingroup\$ Yet again, blaming the tool instead of the user... This must've originated with the first tool-wielding hominids. \$\endgroup\$ Commented Jun 15, 2020 at 21:19
  • \$\begingroup\$ @aconcernedcitizen What on earth are you talking about? \$\endgroup\$
    – W5VO
    Commented Jun 16, 2020 at 2:01
  • \$\begingroup\$ @W5VO "LTspice provides incorrect bode plot", instead of "What am I doing wrong?". The second part was meant to be a tongue-in-cheek sort of remark (it may not appeal to everyone). I didn't use the "add" because the OP would be noticed, anyway, and it's a comment to your answer to try to make it clear for all the participants in this 'thread' (QA, whatever other name it has), but it was addressed to the OP, not to you. Nothing to worry about. :-) \$\endgroup\$ Commented Jun 16, 2020 at 6:12

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