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Simulators >> Circuit Simulators >> Trapezoidal ringing in Cadence
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Message started by inqui123 on Mar 10^th, 2017, 8:51am

Title: Trapezoidal ringing in Cadence
Post by inqui123 on Mar 10^th, 2017, 8:51am

Hi

This is with reference to Ken Kundert's book, The Designer's Guide to Spice and Spectre, Chapter4: Section 4.2.2.1-Stiff circuits under Transient analysis. I am trying to understand the three numerical methods discussed and recreate the graphs shown on page 136-138. The problem is for trapezoidal method, I am unable to see the ringing shown for higher values of pole frequencies. I have tried with very small time constants and very high time steps(forced cadence to follow the required time step only). I changed the settings to Conservative/Liberal and traponly. When I code the same equation in Matlab, the results come as expected. Has the cadence done some error correction for this, and I should indeed not see the trapezoidal ringing in this case?

Title: Re: Trapezoidal ringing in Cadence
Post by Geoffrey_Coram on Mar 10^th, 2017, 11:02am

Are you properly restricting the simulator to use traponly?

Title: Re: Trapezoidal ringing in Cadence
Post by inqui123 on Mar 12^th, 2017, 5:52am

I have checked the traponly in transient options. Is there any other setting pertaining to this as well?

Title: Re: Trapezoidal ringing in Cadence
Post by Ken Kundert on Mar 12^th, 2017, 11:42pm

Spectre, and SPICE in general, always places a backward-euler step at corners. This will make it harder to see the effect you seek as it will suppress the trapezoidal ringing.

-Ken

Title: Re: Trapezoidal ringing in Cadence
Post by inqui123 on Mar 13^th, 2017, 6:43pm

If I understand correctly, the simulator uses break-points at every sharp corner of the stimuli. This circuit, however, has no such source. It is a rc circuit, with an initial condition.
The idea actually is to understand in which circuit to expect trapezoidal ringing, and if there are some differences between theory and practice.

Title: Re: Trapezoidal ringing in Cadence
Post by inqui123 on Mar 16^th, 2017, 6:08am

Any update on the question posted?