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Phase Noise of Oscillator after capacitor (Read 3544 times)
martin88
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Phase Noise of Oscillator after capacitor
Dec 15th, 2016, 5:27am
 
Hi,
I build a oscillator with a buffer stage after it. To cancel out the common voltage I also added a capacitor before the load. My problem now is why the phase noise is almost constant over the offset voltage after this capacitor and doesn't show the decreasing behaviour. See the picture attached.
Hopefully someone knows why the phase noise is looking like that.
Thanks
Regards,
Martin
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Phase_noise_after_Cmim.jpg
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vroy_92
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Re: Phase Noise of Oscillator after capacitor
Reply #1 - Dec 15th, 2016, 5:54am
 
Can you please share a snapshot of the circuit?
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V Roy
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martin88
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Re: Phase Noise of Oscillator after capacitor
Reply #2 - Dec 15th, 2016, 6:12am
 
The setup looks like this:
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setup.PNG
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vroy_92
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Re: Phase Noise of Oscillator after capacitor
Reply #3 - Dec 17th, 2016, 10:02pm
 
This capacitor should not change the phase noise significantly. The phase noise is mostly introduced by the device noise of the ring devices.
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V Roy
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martin88
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Re: Phase Noise of Oscillator after capacitor
Reply #4 - Dec 19th, 2016, 2:36am
 
But before the capacitor the phase noise looks like this:
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Phase_noise_before_Cmim.png
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Ken Kundert
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Re: Phase Noise of Oscillator after capacitor
Reply #5 - Dec 20th, 2016, 12:50pm
 
The first result you gave is clearly wrong. This appears to be a simulator issue. How big is the capacitor you are adding?

-Ken
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martin88
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Re: Phase Noise of Oscillator after capacitor
Reply #6 - Dec 22nd, 2016, 2:33am
 
The capacitor is 8pF.
Thanks for the answers, I will check the testbench again.
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Andrew Beckett
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Re: Phase Noise of Oscillator after capacitor
Reply #7 - Dec 29th, 2016, 10:20am
 
Which MMSIM version are you using (the spectre version will be shown near the top of the spectre log file)? There were some bugs in shooting pnoise (in oscillator mode) prior to MMSIM15.1 which could lead to bizarre results in certain situations (the results were generally obviously wrong when it occurred - it didn't happen all the time), so I'd certainly recommend switching to something more recent.

Andrew.
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