What is the advantage if CDR use external clock reference to extract clock?

[surianova]

hi all!

What is the advantage if CDR use external clock reference to extract clock?

 

[Shohdy]

Re: CDR

Well as far as I know, the CDR's main purpose is to extract the clock from a data flow, this is done usually by adjusting the CDR's internal VCO phase to sample the data flow at the right time.

if it has an external source of clock, then we don't need the CDR at all, as we will sample the data using the external source...am I right???

Regards,
Shohdy

 

[safwatonline]

CDR

CDR is mainly a phase allignment device not a frequency locking device due to the small lock in range consequently if u wanna lock at a certain frequency then use something like CP PLL , note in dual loop CDR a frequency locking loop is added to the phase allignment loop to increase the locking range at the start of allignment.

 

[ericzhang]

CDR

If an external clock is provided, the job of CDR is
easied, which means phase aligment is the only task.
In LVDS/TMDS, a clock link is accomponied with data links, the CDR of the receiver is to extract phase relation between clock and phase. In optical
network, the link is expensive, and there is only
data link, the CDR of the receiver has to extract
both phase and clock from the data, which make it
complicated.