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Simulators >> Circuit Simulators >> Can't get right simulation result from transient simulation
https://designers-guide.org/forum/YaBB.pl?num=1386251235

Message started by Mikay on Dec 5^th, 2013, 5:47am

Title: Can't get right simulation result from transient simulation
Post by Mikay on Dec 5^th, 2013, 5:47am

I have a pure LC(inductor-capacitor) tank set up in the Spectre. The initial voltage for the Cap is 1V and the initial current for the ind is 0A. When I do the transient simulation, different accuracy have different results.

1) when the transient accuracy is "consertive" or "liberal", the output finally settle to 0.
2) when the rtansient accuracy is "moderate". the output is sinusoidal wave.

Since the LC tank is lossless, the tank should oscillate and output is sinusodial.

Anybody know how to deal with this?

-Mikay

Title: Re: Can't get right result from transient simulation
Post by Mikay on Dec 5^th, 2013, 5:48am

The output is attached. Red line is for "moderate" accuracy. Another is for "consertive" accuracy.

Can any explain this?

Title: Re: Can't get right simulation result from transient simulation
Post by Frank Wiedmann on Dec 5^th, 2013, 6:27am

Some integration methods used by circuit simulators exhibit numerical damping. See page 24 of http://www.kenkundert.com/docs/bctm98-MSsim.pdf (or Ken's book http://www.designers-guide.org/Books/dg-spice/index.html).

Title: Re: Can't get right simulation result from transient simulation
Post by Mikay on Dec 5^th, 2013, 6:57am

Thanks Frank. A lot to learn for me.
Frank Wiedmann wrote on Dec 5^th, 2013, 6:27am:

Title: Re: Can't get right simulation result from transient simulation
Post by danmiso on Dec 11^th, 2013, 11:50pm

By default, the conservative and liberal settings use the gear2only integration method which has the damping property Frank mentioned whereas the moderate setting uses the traponly method.

You can manually specify an integration method in the transient simulation option.