What is main difference between CDR and PLL?

[surianova]

what is main different between CDR and PLL?

 

[IanP]

pll+cdr

Some digital data streams, especially high-speed serial data streams, (such as the raw stream of data from the magnetic head of a disk drive) are sent without an accompanying clock. The receiver generates a clock from an approximate frequency reference, and then phase-aligns to the transitions in the data stream with a phase-locked loop (PLL). This process is commonly known as clock and data recovery (CDR).

Quoted from:
"Clock recovery"
https://en.wikipedia.org/wiki/Clock_recovery

Regards,
IanP

 

[safwatonline]

CRD and PLL

the CDR is extracting the clock from random input data while the pll works on a certain frerence clock.

 

[surianova]

Re: CRD and PLL

then how to congfigure PLL to function as CDR?

 

[safwatonline]

CRD and PLL

u cannot , a special PD must be used as it alligins the phase and not like PFD which lock to the frequency

PD used for CDR are as alexander and hogg , refer to razavi's optical communication book for more details

 

[nbj78]

Re: CRD and PLL

between CDR and pll , the different thing is PD scheme , generally

the pfd using in pll always cant use in CDR for pll

because of the data patten , hogge and alexader detect the rising and falling

this meaning is very important and differentation between pll and CDR

if u want to , find the opital book written by RAZAVI

 

[surianova]

Re: CDR and PLL

u cannot , a special PD must be used as it alligins the phase and not like PFD which lock to the frequency

PD used for CDR are as alexander and hogg , refer to razavi's optical communication book for more details

Can u explain to me how clock can be extracted random data bit stream?
Is it need sample and hold circuit? Or is it depend on the filter ?

 

[safwatonline]

CDR and PLL

hello,
for CDR there r some diffrent architectures of PD that can allign the phase of the clock to the ideal sampling point which is the half period point , each of the phase detector have its own theory of operatio there r many types like linear and Binary (bang-bang), u should refer to ch.2 and ch.9 in Razavi's optical communicaion it has good explaination of the theory of PD .

sample and hold can be used to extract the clock.

i dont think the filter has to do with the type of PD , as each of the PD's will be followed by GM-cell or CP to convert Voltage to current and hence the simple series R and C filter is used.
regards,
a.safwat