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TINA/Spice: Example of weirdness with TRANSIENT analysis

jc maillet
Prodigy 90 points
Other Parts Discussed in Thread: TINA-TI

Tool/software: TINA-TI or Spice Models

Hi gang, been using TINA-TI for 5~6 years now,

every once in a while I see strange output, esp. in nested sims (swept parameter)

but this week, I started noticing a very basic problem

something that def. shouldn't be happening

a +/- 5v 1hz square wave is going through an RC stage ... and showing evidence of a decaying voltage from start

ran the sim in both TINA-TI and TINA-10 (purchase)

in both cases TRAN analysis was set with "zero initial values"

as far as I know all simulator settings are set at their default values

got same "non-zero start" results in both cases despite there none being set

never had an issue like this with a circuit simulator

a bit troubling ...

  • 0 in reply to jc maillet
    TI__Prodigy 610 points

    Hi JC,

    We have simulated the same test set up and found the following:

    1) If you zoom the results in the initial part you will see that it is starting from zero only as shown below:

    2) As per the test set up we are applying a square wave of +/-5V with a frequency of 10 hz to a L.P.F with a RC time constant of 5RC=5sec.So the DC value of output which is zero in this case should be passed.Since the Cut off frequency of L.P.F and switching frequency are close some harmonics are present in the output and DC output results  move towards zero DC value with some ripple (200mV)taking 5RC time to become steady.These can be seen in the results shown below.

    Hope this clears your doubts on the simulation results.
    Best Regards,
    Ashis

  • 0 in reply to Ashis Mondal
    Prodigy 90 points

    duh - of course ... thank-you for the explanation Ashis

    ~jcm