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xuel New Member Offline Posts: 5	difference between phase noise testing and simulation Aug 04^th, 2008, 7:33pm In simulation the phasenoise is very good, is 100dbc at 1MHz. But in testing, phasenoise is only 60dbc at 1MHz. But the jitter is not large, 20ps peak-to-peak measured from oscilloscope. Why is the measured phasenoise so bad?
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luantan New Member Offline Posts: 4	Re: difference between phase noise testing and simulation Reply #1 - Aug 10^th, 2008, 8:37am anybody knows?
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ACWWong

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Posts: 539
Oxford, UK

Re: difference between phase noise testing and simulation
Reply #2 - Aug 11^th, 2008, 12:30am

I'm assuming your simulation gives -100dBc/Hz

In such a case your measurement shows about -95dBc/Hz at 1MHz offset.
That is -60dBc in a 3kHz RBW, so you need to adjust the marker by 10*logRBW=34.8 dB.

Often the analyser has the marker on noise function which will take into account the RBW automatically (and more accurately).

So in fact you are 5 to 6 dB of where you expect to be. The reasons for this can be many e.g. discrepenacy in models, simulation setup issues, measurement issues, PCB design, noise pickup etc.....

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iaman

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Posts: 1
China,Shanghai

Re: difference between phase noise testing and simulation
Reply #3 - Sep 12^th, 2008, 8:32am

ACWWong wrote on Aug 11^th, 2008, 12:30am:

I'm assuming your simulation gives -100dBc/Hz

In such a case your measurement shows about -95dBc/Hz at 1MHz offset.
That is -60dBc in a 3kHz RBW, so you need to adjust the marker by 10*logRBW=34.8 dB.

Often the analyser has the marker on noise function which will take into account the RBW automatically (and more accurately).

So in fact you are 5 to 6 dB of where you expect to be. The reasons for this can be many e.g. discrepenacy in models, simulation setup issues, measurement issues, PCB design, noise pickup etc.....

Great.
from the test picture, we can find some details:
1. RBW is 3kHz, so we should normilized the PN to dBm/Hz.
2. the Spectrum analiyzer power dector is peak dector , you should change the power dector to rms dector.
2.

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RFsage New Member Offline Posts: 3 Melbourne, Australia	Re: difference between phase noise testing and simulation Reply #4 - Sep 15^th, 2008, 12:53am The phase noise at higher offset frequencies is generally limited to thermal or white noise floor of your load. If you are using a resistive load you should expect higher noise floor.
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