LTspice syntax problem

It is unlikely that you will be able to do what you want in that way. The fields in the pulse source must be numbers or parameters that can be resolved into a number BEFORE the beginning of the simulation. If you are trying to create a PWM signal with a fixed frequency and a variable duty cycle that will respond to a control voltage, there are better ways to accomplish that.

You could use something like this, where the duty cycle varies with v(a) :-

I am an LTspice newbie and just learned how to do this

Using two interpolated pulses to make two sawtooths with 1000:1 T ratio = 10ms:10us compared with an arbitrary IF statement to make a PWM signal.




For those curious why I use Win7 x64 16GB instead of Win 10/11, it's because I like lean and fast on my 10 yr old PC.