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  

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).

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.