Electronics > Projects, Designs, and Technical Stuff
LTSpice pulse options
iMo:
An example:
The square red or green wave/trace you see in the picture has unlimited numbers of "points".
The rising and falling edges are there, in those unlimited numbers.. You cannot see them because of set zoom. You can zoom in, however.
I selected 16.7mil of them for FFT.
I can select the entire 10ns transient sim time for FFT. And the trace will be split into the 16.7mil points.
Simon:
So what is the smalest time step in the simulation for?
Simon:
Sorry it's the maximum not the minimum i am looking at. So presumably it decides the minimum by itself and is then allowed to use up to the maximum when it detects a steady state condition.
iMo:
Spice is adjusting the "time steps" dynamically during the transient simulation such it gets best results within required voltage/current tolerances.
Imagine you do transient analysis 1sec long of a circuit.
When the circuit is "smooth enough" (from math point) it uses "large steps".
When there is a lot of nonlinearities (ie complex highly nonlinear models), the time step could decrease such the iteration results are "smooth enough".
There is not such setting like min step therefore.
You may set for the transient analysis a "maximum timestep" that forces the solver not to use "large" steps when the iterations are already within the abs/rel V/A tolerances.
Simon:
And the FFT on 1'000 cycles is completely different from what it is on 20 cycles
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