Failed Harmonic Balance of Oscillator using ADS - RF Cafe Forums
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Post subject: Failed Harmonic Balance of Oscillator
using ADS Posted: Fri Jul 18, 2008 10:54 am
Joined: Tue Feb 27, 2007 6:16 am
I have managed to gain access to the use of the ADS simulator.
Below is an Oscillator I modified for my purposes.
Below is the results of the S parameter simulation. As you can see
it appears to oscillate at 120MHz.
Unfortunately when I
try and perform the Harmonic Balance Simulation (I wish to determine
phase noise), the simulation fails.
Does anyone have
any suggestions as to how I can correct the problem?
Regards, Darcy Randall, Perth, Western Australia
Post subject: Posted: Fri Jul
18, 2008 10:57 am
Joined: Tue Feb 27, 2007
On a last note, referring to the results figure,
whats the difference between the option of plotting analysis.sp1.s(1,1)
Darcy Randall, Perth, Western Australia
Post subject: Posted: Fri Jul 18, 2008 4:33 pm
Joined: Tue Jul 08, 2008 7:15 pm
It looks like you are trying to model a
crystal oscillator. It can be difficult for simulators to converge when
circuits have very high Q. This is because small steps in frequency
can cause large jumps in voltage and current which gives simulators
With the circuit shown, it looks like the crystal will
be inductive at resonance, and will resonate with the two series caps.
I would start by calculating an inductor that will resonate with caps,
and see if simulator converges. Modify inductor to get desired frequency.
Then insert series (Rm) with inductor, and see circuit has enough loop
gain to sustain oscillation. You may need to change ratio of caps to
improve margin. At this point, it will be likely your XO will at least
- Mark -