Re: [usb] question about the DLL in the UTMI

[Jiang daosan <jiangdaosan@21cn.com>]

 Hi, Luis:

     Thank you so much for your answer.  However, I think there maybe something
to talk about more, As you written:
>To design a HS PLL you need an external clock of 480x4 MHz (at least, I
>think) to obtain the data signal synchronized with the internally
>extracted 480 MHz clock.
I was wonder that there is some mistake? As the external clock of 480x4 MHz is 
so high, it may be impossibe in practice. I saw the needed external clock in
Phlips ISP1501 is 12MHz. In my opinion, the internal local 480MHz clock is 
produced by the Clock Multiplier with the external 12MHz Clock in the UTM,
And then it was made some Phase delay by the HS DLL to synchronized to the clock of 
the incoming data. That delayed Clock is the exacted clock. Am I right ?    

     
2001-09-18 09:59:00  you wrote£º
>Hello Jiang daosan,
>
>I think that the named "local clock" is the external clock you need to
>generate the "extracted clock", and also used as CLK OUT to the USB
>Device controller. So, the extracted clock is a 12 MHz or 480 MHz (FS or
>HS) clock generated from the external clock (divide it!).
>To design a HS PLL you need an external clock of 480x4 MHz (at least, I
>think) to obtain the data signal synchronized with the internally
>extracted 480 MHz clock.
>
>The need of extracting the clock from the received data is to syncronize
>it with the incoming clock from the HOST/HUB controller.
>
>The clock used to sample the received data is the external (30, 48, 60
>MHz, it depends on you..., and your design).
>
>About the term "delay line", as you need to sample the received data and
>generate the internal clock, the output data from the DPLL will be
>delayed from the incoming data from the USB wire.
>
>Well, I also WAS puzzled with DLL a month ago, and I've learned a lot
>from the people in this list.
>
>I wish my answers (if no mistake: please, correct me if I'm confused)
>will solve your doubts...
>
>Regards,
>
>  --- Luis ---





*************************************************
Jiang daosan   jiangdaosan@21cn.com

Institute of RF&OE-IC of Soutneast University
http://iroi.seu.edu.cn/english/new/index.htm
Nanjing, China
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