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harpoon Senior Member Offline Posts: 112 Hampshire	How to determine the delay in the reset pulse of a PFD ? Aug 15^th, 2011, 2:51am A classic way of avoiding the dead band zone in a standard PFD is to insert a delay in the reset line. Does anyone know how to determine how long/short this delay should be ? Thanks.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to determine the delay in the reset pulse of a PFD ? Reply #1 - Aug 15^th, 2011, 5:30am hello, higher the delay in reset path, will increase the static phase offset. So many people will add enough delay which can ensure no dead-zone. In many cases this will be done by simulations rather than expressions. Thanks.
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purplewolf Senior Member Offline Posts: 103	Re: How to determine the delay in the reset pulse of a PFD ? Reply #2 - Aug 15^th, 2011, 5:41am i would like to know how to plot vout vs phase error to see the dead zone in the first place
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raja.cedt

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Re: How to determine the delay in the reset pulse of a PFD ?
Reply #3 - Aug 16^th, 2011, 12:37am

hello,
so now i understood your question, you mean to ask how to simulate.

So conect loopfilter cap at the o/p of the charge pump and sweep the phase difference between refclk and fb clk from lag to lead. Then plot the current thorugh the filter cap vs phase difference between refclk and fbclk.

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harpoon Senior Member Offline Posts: 112 Hampshire	Re: How to determine the delay in the reset pulse of a PFD ? Reply #4 - Aug 16^th, 2011, 1:25am opps ... it appears my post has been hijacked and relocated. @raja.cedt, you understood my question correctly the first time. My questions is what determines the lower and upper limit of this reset pulse delay ? If the delay is too long, what effect does it have on the PLL ? Thanks.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to determine the delay in the reset pulse of a PFD ? Reply #5 - Aug 16^th, 2011, 2:55am if delay is too long, then both charge pumps turn on for more time, so more ripple on the control voltage hence ref spurs.......
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harpoon Senior Member Offline Posts: 112 Hampshire	Re: How to determine the delay in the reset pulse of a PFD ? Reply #6 - Aug 16^th, 2011, 3:58am so the shorter the better ? i.e. just enough over process, voltage and temp thanks.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to determine the delay in the reset pulse of a PFD ? Reply #7 - Aug 16^th, 2011, 5:44am yes..you are correct. Make sure than you don't have dead zone across PVT.
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harpoon Senior Member Offline Posts: 112 Hampshire	Re: How to determine the delay in the reset pulse of a PFD ? Reply #8 - Aug 16^th, 2011, 5:57am @raja.cedt thanks for the speedy reply ...
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