HdrChopper wrote on May 23rd, 2009, 10:58am:you should start thinking the modelling of your parasitics might not be good enough, since transient analysis should reflect the actual stability condition of the system....
I don't think so.
Results of Transient Analysis are very affected by initial conditions or startup conditions.
This is very true for weak parasitic oscillation.
http://www.designers-guide.org/Forum/YaBB.pl?num=1234428781/7#7I used same initial conditions and startup pulse(voltage supply rampup) for Cadence Spectre and Agilent GoldenGate.
Transient Analysis(both traponly and gear2only) of Cadence Spectre don't show any remarkable oscillation.
Envelope Transient Analysis of Agilent GoldenGate also don't show any remarkable oscillation, here waveforms of this result are completely same as results of Transient Analysis of Cadence Spectre.
On the other hand, Transient Analysis(gear2) of Agilent GoldenGate show remarkable oscillation which is relatively close to actual phenomena.
I suspect that treatments during initial phase are different between Cadence Spectre and Agilent GoldenGate.
If circuits are in very critical "Conditionally Stable State" at DC operation points, behavior during initial phase is very important regarding whether circuits show oscillation or not.
http://www.designers-guide.org/Forum/YaBB.pl?num=1190272820I can set very unstable conditions by decreasing decoupling capacitor value.
When I create very unstable conditions, both Cadence Spectre and Agilent GoldenGate give same oscillation waveforms.