I'm having issues with a circuit I'm trying to build using analog multiplier AD633. I downloaded the model from the official site.

I included it in the schematic using the guide provided by LTspice: I created a new .asy, inserted it into the LTspice schematic, then I copied the .SUBCKT directive inside a SPICE directive.

I insert some screenshots to illustrate what i did:

The first one is the first line of the circuit I downloaded:

.SUBCKT directive

Here it shows the symbol created in LTspice to represent it.

.asy simbol created

Everything works fine if I simulate one AD633 multiplying one signal for itself. The issues begin when I put in the third copy if this component: the timestep becomes too small, the simulation crashes, and I can't understand why.

If I remove component U3 from the following circuit everything works. I underline the fact that the circuits are completely decoupled from each other.

enter image description here

  • \$\begingroup\$ The U4 circuit doesn't appear to do anything useful so, why is it present? Maybe try making it a squarer like U2 and U3? \$\endgroup\$
    – Andy aka
    Commented Mar 21 at 13:00
  • \$\begingroup\$ Thank you for your answer. I edited the QUESTION. However in the previous picture U4 did actually nothing, but it was inserted to show that the addition of a third component, even if completely decoupled, resulted in an error \$\endgroup\$ Commented Mar 21 at 14:18

1 Answer 1


You need some way to connect those circuits together. One of the problems you are having is The duplication of circuits makes a matrix that is hard to solve. The reason for this is you essentially have three sets of independently parallel equations, this makes systems of equations hard to solve. Since there is no reason to really have parallel circuits and simulation that are doing exactly the same thing it would be better to either leave them off or connect them together in the way you intended.

Another thing that could help is putting series resistance on the VCC rails.

  • \$\begingroup\$ The reason why I put this in parallel is that: I have to make a project of an analog circuit of a dynamical system; only then, if in simulation it works realize the real thing. I need more or less 6 analog multipliers for this circuit and some of these stages will be independent from the other. Thanks for the hints, I'll upload the main question \$\endgroup\$ Commented Mar 21 at 15:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.