"Timestep too small" error in proteus

Discussion in 'Digital Circuit Design' started by A.N_1994, Jun 19, 2017.

  1. A.N_1994

    Thread Starter New Member

    Jun 19, 2017
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    Hello
    I simulated a simple pmos current mirror circuit with a pulse current source as reference in proteus 8. But it gives the following error:
    transient GMIN stepping at time = ...
    Timestep too small; ...
    Can anybody help?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    Have you given the current source a finite resistance?
    Have you tried making the two PMOS devices slightly different rather than identical?
     
  3. crutschow

    Expert

    Mar 14, 2008
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    The source of a timestep error in Spice can be hard to pinpoint.
    Sometimes just a small change in the circuit will eliminate the problem.
    Try removing part of the circuit at a time to see if you can determine, which area is the problem.

    Also you might go into the Spice transient simulation values and try reducing some of the default accuracy parameters by a factor of 10 (shown below in the righthand column from LTspice).
    If you can change the default integration method to Gear, that also sometimes helps.

    upload_2017-6-19_12-14-15.png
     
  4. A.N_1994

    Thread Starter New Member

    Jun 19, 2017
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    Thanks for your reply.
    Putting resistance doesn't help, but I don't know how to change transistor properties in proteus.
     
  5. A.N_1994

    Thread Starter New Member

    Jun 19, 2017
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    Thank you.
    But I simulated the circuit in proteus not spice, how can we change transient simulation values in proteus?
     
  6. A.N_1994

    Thread Starter New Member

    Jun 19, 2017
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    And I should add that when I change reference current from pulse to dc current source, it answers properly.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    I'm not familiar with Proteus, but I would think it uses a Spice engine with Spice simulation parameters.
    Most available analog simulators use Spice as the basis for the calculations.
    You need to search for simulation options in Proteus.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Try adding, say, 1 milliOhm in series with the emitter of one (only one) of the transistors forming the current mirror. The intention is to avoid exact symmetry so that Spice/Proteus isn't trying to assign two values to the same node at exactly the same instant (as far as I understand the machinations of Spice ..... which could be way off :) ).
     
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