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Urgent！Problem about a 1GHz PLL。&#

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linlin

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:!: I think my Pll has gone to its steady state because the output of PDF is unchanged. But the control voltage oscillate. Is there somebody who can tell me why the control voltage oscillate?

The wave is attached in the PPT. Thanks very much!
 

Re: Urgent！Problem about a 1GHz PLL。&a

I really need some guidance, please help~

linlin said:
:!: I think my Pll has gone to its steady state because the output of PDF is unchanged. But the control voltage oscillate. Is there somebody who can tell me why the control voltage oscillate?

The wave is attached in the PPT. Thanks very much!
Click to expand...
 

Re: Urgent！Problem about a 1GHz PLL。&a

q1,2> check the bandwith/Fref and damp factor of your pll; check your PDF dead zoom, the output of PDF1 is 0.7v when locked, does this pulse can open the charge pump?

q3> your PDF is not shown, if phase error is 180degree, PDF must have a big output, I think.

q4> check the high frequency divider, does your divider can work well at 1GHz?
the divide ratio from VCO out to feedback is right?


good luck!

fish
 

Re: Urgent！Problem about a 1GHz PLL。&a

To butterfish: Thanks very much for your help. I didn't realise that the output of PFD1 is only 0.7V until you mention it. I don't know if it is the problem. I will check and give more details about my PLL. I am a novice in Analog Circuit design. Hope to get more help from you. Thanks very much for your kindness and patience.

Best regards,

Linlin
 

Re: Urgent！Problem about a 1GHz PLL。&a

you are wellcome.
The PDF should be PFD.

fish
 

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