Failed Harmonic Balance of Oscillator using ADS - RF Cafe Forums

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darcyrandall2004
Post subject: Failed Harmonic Balance of Oscillator using ADS Posted: Fri Jul 18, 2008 10:54 am

Colonel


Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
Hello,

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?

Thankyou

_________________
Regards, Darcy Randall, Perth, Western Australia


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darcyrandall2004
Post subject: Posted: Fri Jul 18, 2008 10:57 am

Colonel


Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
On a last note, referring to the results figure, whats the difference between the option of plotting analysis.sp1.s(1,1) and sp1.s(1,1)

Thankyou

_________________
Regards, Darcy Randall, Perth, Western Australia


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markapexwireless
Post subject: Posted: Fri Jul 18, 2008 4:33 pm

Captain

Joined: Tue Jul 08, 2008 7:15 pm
Posts: 11
Location: Boulder Colorado
Darcy,

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 fits.

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 fire up.

Good luck,

- Mark -



Posted  11/12/2012