cadence simulation setting

[whlinfei]

Hi all,

I try to simulate transient response of my circuit, ( a bit large as it's a complete ic)

However, there are some nodes which continuously oscilates within a very small range in a triangular wave shape.

I double checked my circuits, which should have enough phase margine.
Also if there is really phase margin issue, the wave should be sinusoidal I guess.

So I assume problem lies with my simulation settings..

Can anyone help me on that ?

Thank you!

 

[erikl]

Which simulator do you use, and which integration method?
If you used trap or traponly, try and select gear2, gear2only or even euler.

 

[whlinfei]

Which simulator do you use, and which integration method?
If you used trap or traponly, try and select gear2, gear2only or even euler.

Hi
thank you for your reply.

I use Spectra and the method I use is traponly. I heard it was the most accurate one.
Not sure on that though.

Would you kindly tell me which method to select and what the differences are?

Thank you so much.

Best Regards,
Linfei

 

[erikl]

Would you kindly tell me which method to select and what the differences are?

I already told you above:

If you used trap or traponly, try and select gear2, gear2only or even euler.

For the differences, study e.g. Kenneth S. Kundert's book "The Designers Guide to SPICE & SPECTRE", especially the 4.2.2 chapter on "Characteristics of the Integration Methods" (about 25 pages).
Here just a few clippings: "trapezoidal rule exhibits strong point-to-point ringing." (p.135); "backward Euler exhibits heavy damping" (p.147); "trapezoidal ringing" (p.150); "To avoid trapezoidal ringing, use Gear2" (p.155).

If you set Spectre's errpreset property to conservative, the gear2only method is used by default. I'd suggest to use this one first.