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Design >> RF Design >> Hooking up VCO and prescaler
https://designers-guide.org/forum/YaBB.pl?num=1107802271

Message started by gogomi on Feb 7^th, 2005, 10:51am

Title: Hooking up VCO and prescaler
Post by gogomi on Feb 7^th, 2005, 10:51am

Hi,

I am working on a fractional-N PLL design and I am having trouble
with the interface from VCO to prescaler. I used a complementary
LC-VCO in my design, which has a 1/2 Vdd DC bias voltage at
the output, and I used CML latches in the prescaler. If I hook them
up directly, it looks the DC voltage from VCO puts the prescaler
latches on all the time. I don't know if there is a good way to solve
this kind of problem without degrading the performance too much.
Thank you for your help!

gogomi

Title: Re: Hooking up VCO and prescaler
Post by DReynolds on Apr 14^th, 2005, 5:59am

Gogomi, I am not sure I understand your problem: what is your vco output swing when you have the latches attached? Worst case, why not ac couple and set your dc level on the latches yourself?

David Reynolds

Title: Re: Hooking up VCO and prescaler
Post by wued on Apr 21^st, 2005, 10:48pm

Hi,
I donot think it is a good way to connected them together directly,why not use a buffer.The buffer may be a CML one,there is not level problem.