ADPLL - How to design linear DCO ?

[ashik_na]

Hi All,
I am designing ADPLL for video applications.
For this ADPLL, I am using DCO as oscillator.
Delay cells are used to generate the oscillation.
But frequency chara ( Freq Vs Code ) of the DCO is not linear.
there is large Δfreq, change at high frequencies for small change in code by comparing with lower frequency side.
For eg - Please see the below table
Code Freq( MHz)
0 530
1 309
2 230
3 181
4 151
5 128
6 112
7 100
8 89

I want to design a linear DCO. What is the possible designs to get the linear frequency chara ?
I am a little confused how these type ADPLL will get locked with this DCO behavior .
Could you Please clarify ?
Thanks in advance..!!

 

[neoflash]

First, your question doesn't make sense. It shows that you don't know what you are doing.

What I can suggest is go back buy and read the text book about different types of VCO and the loop dynamics of PLL.

 

[ashik_na]

hi,
this is not about VCO. i am telling about DCO ( Digital Controlled oscillators )

 

[neoflash]

Thanks for clarifying that. Good luck.

:wink: