I want to compare signals from my fancy subcircuit (very complex) and multiple subcircuits level1 (should be almost equivalent, but simpler) with different parameters; these parameters should be passed to level2 subcircuits.

Below is a (simplified) nonworking sample code:

Xfncy 2 0 fancy
Xlvl10 2 0 level1 PARAMS: Y1=1 Y2=1
Xlvl11 2 0 level1 PARAMS: Y1=1 Y2=10
Xlvl12 2 0 level1 PARAMS: Y1=10 Y2=1
Xlvl13 2 0 level1 PARAMS: Y1=10 Y2=10

.SUBCKT fancy 1 2 
.ENDS fancy

.SUBCKT level1 1 2 PARAMS: Y1=1 Y2=2

.param Z10=1 Z20=1 Z11=1 Z21=1 Z12=1 Z22=1

Xlvl20 1 2 level2 PARAMS: Y3=Z10*Y1 Y3=Z20*Y2
Xlvl21 1 2 level2 PARAMS: Y3=Z11*Y1 Y4=Z21*Y2
Xlvl28 1 2 level2 PARAMS: Y3=Z18*Y1 Y4=Z28*Y2

.SUBCKT level2 1 2 PARAMS: Y3=1 Y4=1
.ENDS level2
.ENDS level1

Running like this, I get the following error:

WARNING: Can't resolve .param Y3=Z10*Y1

Select OK to continue the simulation with the default model or Cancel to quit now

My first version of the instance Xlvl20 line:

Xlvl20 1 2 level2 PARAMS: Y3={Z10*Y1} Y3={Z20*Y2}

yields the same error. If I change the line to:

Xlvl20 1 2 level2 PARAMS: {Y3=Z10*Y1 Y3=Z20*Y2}

I get:

Missing expression in

"{Y3=Z10*Y1 Y3=Z20*Y2}"

Is passing parameters like this even possible in LTSpice and if so, how? Alternative approaches are also welcome.

PS: Yes, I've tried .step param to avoid packing level1 stuff into a subcircuit, but then I can't compare it to fancy, because fancy takes about 30 times more time to simulate.

  • \$\begingroup\$ It looks like you're defining Y3 twice. That could be the issue. \$\endgroup\$
    – herrtim
    Sep 20, 2016 at 10:21

1 Answer 1


The LTSpice manual gives an example of how to do this:

* calling a subcircuit
* This is the circuit
X1 in out 0 divider top=9K bot=1K
V1 in 0 pulse(0 1 0 .5m .5m 0 1m)

* This is the subcircuit
.subckt divider A B C
R1 A B {top}
R2 B C {bot}
.ends divider
.tran 3m

The full syntax is given as:

Syntax: Xxxx n1 n2 n3... <subckt name> [<parameter>=<expression>] 

The rules for writing expressions are given in the section of the manual on "arbitrary behavioral voltage and current sources".


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