How to use .step param with more than two parameters in LTSpiceIV

I need to do three transient simulations with different values of certain resistors (conveniently called R1 and R2) in each. What I mean to do exactly is this:

• Sim. 1: R1 = 1 k$\Omega$, R2 = 10 k$\Omega$
• Sim. 2: R1 = 1 M$\Omega$, R2 = 10 M$\Omega$
• Sim. 3: R1 = 1 k$\Omega$, R2 = 1 M$\Omega$

If there were just one resistor whose resistance to vary, then I would just set its resistance to "{r1}" (I use lower case letters to make it a different variable/parameter than R1) and use a command such as:

.step param r1 list 1k 1meg 1k


However, since I have to change two parameters (together) two times each, I have read here that (at least on LTSpiceIV) that a workaround to my problem could be using something like this:

.step param X list 1 2 3

.param r1 = table(X, 1k, 1meg, 1k)

.param r2 = table(X, 10k, 1meg, 10meg)


Upon doing the simulation, I get the following warnings:

WARNING: Can´t resolve .param r2 = table(X, 10k, 1meg, 10meg)
Select OK to continue the simulation with the default model or Cancel to quit now.


The same applies for r1.

For some reason, the simulation doesn´t "break" if I add one extra element to the table. In that case, the simulation takes too long, advancing more slowly every time, as it would never end. I have tried setting X to 0 1 2 instead of 1 2 3, but that does not work either.

Here are some pictures:

Circuit + commands

Error message

Your help would be much appreciated.

• I'm confused, do you want to simulate 3 situations or more? If you just want to simulate the 3 scenarios I wouldn't bother doing it with spice. – ACD Aug 26 '14 at 20:32
• And what do you want the X axis to be? – ACD Aug 26 '14 at 21:02
• I would like to simulate those three situations and plot them together. I know I could just export a CSV file and plot them with Octave or Excel, but it would be so much more useful to do it directly on LTSpice. In this post (electronics.stackexchange.com/questions/20811/…) someone said how to do it but it doesn't work for me. In this example I put three scenarios but I might need to put more. – sebascarra Aug 28 '14 at 13:28
• As regards your second question, X would be the different indexes that let me access the table's values. Since (apparently) LT will only allow me to sweep through one variable at a time, I sweep through X and then I try to access the table's values according to the value that X has taken in that step. I hope I'm being clear. Thank you. – sebascarra Aug 28 '14 at 13:31
• Well for one the table command wants an index, which is X, then a set of xy pairs. Each param should have 3 pairs in it, not three values. – ACD Aug 28 '14 at 13:53

In LTSpice the table command really creates a kind of dictionary where you have to specify key value pairs. The proper directive for your case would then be:

.step param Rx list 1 2 3
.param R1 table(Rx,1,1k,2,1Meg,3,1k)
.param R2 table(Rx,1,10k,2,1Meg,3,10Meg)


and set the value of the resistors to {R1} and {R2} respectively.

If you want to have the values of a resistor near to it, you can also enter (instead of value, when right clicking onto it)

R=table(Rx,1,10k,2,1Meg,3,10Meg)


into the resistor value field. This works the same way for all kinds of components and with an external script to create .asc files it can be used as a crutch for LTspices missing monte carlo functonality.

One parameter sweep/step can control multiple component values through expressions.

Your control variable you are stepping could be a phase angle or time delay or similar that you input in one or more formulas/expressions to obtain resulting component values or parameters to be applied in the design as {parameter}

This is useful if you want to maintain a relation or control some indirect physical property of the design like a current or filter property.

In the "op" command editor you can enter something like this:

.STEP param Imax 0.1 0.3 0.1
.PARAM Uin= 5
.PARAM R = (Uin-0.84954605)/Imax


It steps Imax from 0.1 to 0.3 in steps of 0.1 and computes a resistor value R using parameter Imax, Uin, some assumed voltage drop 0.85.. of a diode.

The PARAM R can be referenced in a component value usng {R} notation. Notice Uin could be used as {Uin} in a voltage source or similar and so on.

For multiple lines in the "op" editor window use CTRL+M to keep all params in same textbox.