Harmonic Balance -LC Oscillator

Hi all,

I am facing a weird issue. When I am simulating a LC Oscillator in HB, the Estimated oscillating frequency from Tstab Tran differs around 1GHz from the calculated fundamental frequency. The oscillator aims to oscillate in 11.5Ghz.

When I am saying "Estimated oscillating frequency from Tstab", I am referring to the frequency that SpectreRF simulator calculates after the simulation is done. It's written in the output log file.

I have followed all the recommended settings that MMSIM 14.1 Spectre RF document proposes, such as:

A] Transient-Aided Options: 1) Run Transient -->either YES  or Decide automatically

                                                   2) Detect Steady State -->YES

                     3) tstab= 30n

B] Fundamental Freq =12G

    Number of Harmonics =12

    Over-sample Factor = 12

C] Accuracy: conservative

D] Options button:

1)Integration method tstab: I tried both traponly and trap. I am getting the same freq. deviation

2)maxstep=1psec,350f --> I am getting the same freq. deviation

The testbench is consisted  of:  1) the extracted view of the capacitor bank and the GM circuit

                                                         2) N-Port S -parameter file for the inductor and the tracks (extracted from EMX tool)

From my previous experience, the estimated osc. frequency from tstab tran is a bit close to the fundamental freq. 

My questions are: 1) Could anybody tell me what is the reason behind this big deviation? Did anyone has experienced similar HB/tstab behavior?

   2) Is it safe as a verification check to run the same testbench in Transient analysis and set the stop time around 200nsec and then measure the frequency using the "freq" function from the calculator    menu?

Thanks in advance