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aaron_do

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closed loop direct vco modulation bandwidth limit
Mar 15^th, 2012, 7:50am

hi all,

Can anybody tell me what I'd the maximum signal bandwidth we could have for a closed-loop direct modulation vco? I'm also interested in knowing the main limitations. Basically I want my output phase to track my reference phase, and I want to know how fast can I expect to make my reference phase change...

Thanks,
Aaron

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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: closed loop direct vco modulation bandwidth limit Reply #1 - Mar 15^th, 2012, 8:19am loop bandwidth. Thanks, raj.
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: closed loop direct vco modulation bandwidth limit Reply #2 - Mar 15^th, 2012, 11:33am Less than the loop bandwidth. If you want to maintain phase errors low you don't want to be near the edge of the loop BW.
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aaron_do

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Re: closed loop direct vco modulation bandwidth limit
Reply #3 - Mar 16^th, 2012, 6:32pm

Hi,

thanks. Yes I suspected the answer was as simple as that. So can anybody tell me what kind of loop bandwidth is possible and roughly how much power consumption it would take?

So I want to actually divide from 2 GHz to some reference frequency (up to me to define), but I need my loop bandwidth to be large. Is it possible to achieve a 100 MHz loop bandwidth? I understand that for an integer-n PLL, the reference frequency is usually around 10* the loop bandwidth. So does that rule out such a simple architecture?

thanks,
Aaron

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: closed loop direct vco modulation bandwidth limit Reply #4 - Mar 16^th, 2012, 6:41pm Your reference frequency which, in lock, will end up being seen by the charge pump, needs to hit a loop filter where they do not feed through the filter. So, higher the reference frequency the higher you can push the loop BW.
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