vco phase noise simulation problem in ADS

ads simulation phase noise

hello all:

i use ads to simulate vco phase noise, but the simulator gives a warning and no results can be obtained.(the vco config is showed in the attached pic). the vco can work normally under tran simulation,the warning information seems so strange. can some one give some suggestion. thanks

gargoyle


Simulation / Synthesis Messages


Warning detected by HPEESOFSIM in frequency search during HB analysis `HB2'.
Cannot find a frequency where small signal loop gain phase equals 0.0 deg.
The magnitude of the loop gain is greater than one but additional phase
shift around the loop is needed. Will try fixed frequency amplitude search.
Error detected by HPEESOFSIM in arc-length continuation during HB analysis `HB2'.
Cannot sweep to desired level.
Try decreasing MaxShrinkage and re-simulating.
Warning detected by HPEESOFSIM during HB analysis `HB2'.
Oscillator analysis did not converge. Setting solution to zero.
Warning detected by HPEESOFSIM during HB analysis `HB2'.
More than one mixing term has landed on frequency 0 Hz.