how to run the simulaiton for 1 ns step interval ..?

Sunil,

You cannot constrain the "minimum" simulation time. If the simulator is taking very short timesteps, it does so in order to ensure it accurately follows the signals - if you were able to stop it doing this, it could easily become inaccurate as it would then miss vital detail.

What can cause short timesteps? Here's a few suggestions:

1. Check that you don't have very sharp edges on voltage or current sources. The simulator will need to zoom the timestep in to follow the sharp edges, so that's not a good thing.
2. Very large component values (e.g. very large inductors and capacitors) can cause instability and oscillation
3. Are you over-tightening the tolerances? Start by leaving as many settings (e.g. reltol, vabsol, iabstol, etc) at default, and just use errpreset=liberal or errpreset=moderate on the transient analysis
4. Discontinuities in device models can cause problems, especially if there is insufficient parasitic capacitance to damp out the discontinuities. Using cmin=1f or cmin=0.1f as a transient option can help (this adds a capacitance to ground from every node). Be careful of this though...
5. Try using APS (spectre +aps in the latest releases) to see if that helps to speed up the simulation
6. Speak to Cadence Customer Support to get more advice - and maybe somebody can look at your simulation setup and output logs to give more specific advice.

Regards,

Andrew.

Sunil,

You cannot constrain the "minimum" simulation time. If the simulator is taking very short timesteps, it does so in order to ensure it accurately follows the signals - if you were able to stop it doing this, it could easily become inaccurate as it would then miss vital detail.

What can cause short timesteps? Here's a few suggestions:

1. Check that you don't have very sharp edges on voltage or current sources. The simulator will need to zoom the timestep in to follow the sharp edges, so that's not a good thing.
2. Very large component values (e.g. very large inductors and capacitors) can cause instability and oscillation
3. Are you over-tightening the tolerances? Start by leaving as many settings (e.g. reltol, vabsol, iabstol, etc) at default, and just use errpreset=liberal or errpreset=moderate on the transient analysis
4. Discontinuities in device models can cause problems, especially if there is insufficient parasitic capacitance to damp out the discontinuities. Using cmin=1f or cmin=0.1f as a transient option can help (this adds a capacitance to ground from every node). Be careful of this though...
5. Try using APS (spectre +aps in the latest releases) to see if that helps to speed up the simulation
6. Speak to Cadence Customer Support to get more advice - and maybe somebody can look at your simulation setup and output logs to give more specific advice.

Regards,

Andrew.