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Design >> Mixed-Signal Design >> closed loop direct vco modulation bandwidth limit
https://designers-guide.org/forum/YaBB.pl?num=1331823017

Message started by aaron_do on Mar 15^th, 2012, 7:50am

Title: closed loop direct vco modulation bandwidth limit
Post by aaron_do on 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

Title: Re: closed loop direct vco modulation bandwidth limit
Post by raja.cedt on Mar 15^th, 2012, 8:19am

loop bandwidth.

Thanks,
raj.

Title: Re: closed loop direct vco modulation bandwidth limit
Post by loose-electron on 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.

Title: Re: closed loop direct vco modulation bandwidth limit
Post by aaron_do on 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

Title: Re: closed loop direct vco modulation bandwidth limit
Post by loose-electron on 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.