Circuit Simulation packages?

Discussion in 'General Electronics Chat' started by Shocker33, Sep 18, 2015.

  1. Shocker33

    Thread Starter New Member

    Oct 28, 2013

    Are there any differences in circuit simulation packages and what they're used for?

    I have a circuit, where the signal has step raise/fall times of approximately 1ns. I want to see how the signal propagates through the circuit and i also want to see how parasitics of the circuit affect signal integrity, as i want the steps in voltage to settle within a nanosecond or two. With a rise time of about 1ns, i'm looking at harmonics at up to about 300-400MHz.

    The circuit takes a digital input, amplifies it, where it turns it in to an analog signal and continues to be an analog signal until it reaches the output.

    I've tried simulated traces as lossy transmission lines, and components with their parasitic elements in Multisim but it doesn't seem to like it because after so many picoseconds the simulation halts and it tells me that the step size is too small. I only have the step sizes at a moderate 0.1ns, which is only 10 times greater than my signal. I can't increase my step size because then i will completely loose the detail that i'm interested in.

    The circuit simulated before i turned the traces in to transmission lines. I thought about simulating the transmission lines as RLC circuits, but this will give inaccurate results.

    I've thought about going to other simulation packages such as LTSpice, Hyperlynx, ADS but i don't know if they'll be advantageous? Or whether i'll be just wasting my time and should stick with Multisim?

    My PCB is designed using Mentor Graphics, and so Hyperlynx is a potential option because it comes as part of the package. I'm also led to believe it has the ability to simulate each trace with how it's laid out on the PCB. Not sure if this is correct or not.

    I've tried doing a bit of Googling but i haven't found anything that gives me the type of answers that i've looking for.

  2. crutschow


    Mar 14, 2008
    Convergence problems are common to all Spice derived simulators (of which Multisim is an example).
    The minimum step size is not the value you selected, it's an internal size it selects during the simulation.
    If you post your circuit I might be able to give you some suggestions to help.
  3. dannyf

    Well-Known Member

    Sep 13, 2015
    Without knowing anything, the chance of two or more things are the same is quite remote, especially for something as complex as simulation.

    Having said that, the single biggest factor for a reasonably good simulator is the models.