hmm.....interesting.
Does the Q of the varactor show a Dip at CM voltage ???
If possible, pls. post the graph of Qvaractor vs. Input Current.
if it were the case, then i doubt it would show the effect you originally quoted.
Quote:If I reduce back to the current, it looks ok and have wider tuning range.
It should have shown same behaviour approaching from both sides.
Have you checked Raja's point whether simulator converged properly at those spiky points ?