CDR tracks only in-band modulation like SSC and low frequency sinusoidal modulation. If the '+100ppm' is directly added to the frequency without modulation, then you are running the serdes with a different refclk, which is 161.146MHz, instead of 161.13MHz. Many serdes applications calls for using this kind of timing scheme called plesiochronous timing where Tx runs at a slightly different clock frequency from Rx or vice versa. Regards, TK -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of prasad Sent: Thursday, April 05, 2012 9:55 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] to what extent recovered clock depends on the serdes ref clock Hi everyone, might this be a fundamental question. If this can be answered by some self reading, please point me to the source of such notes. Thanks in advance. My question is , to what extent the recovered clock of the CDR inside the SERDES depend on the reference clock given to it? I believe the RX side of the SERDES uses the input ref clock given to it as a guiding clock , to track the incomind data signal. which means, for eg, if I/p serial signal is at 10.3125Gbps ( 10GELAN) serdes is of BW 64 on parallel side ( FYI this is IBM HSS11G serdes) ref clock given is 161.13MHz ( 10.3125G/64, this gets multiplied by HSPLL to generate the guiding clock fr the serdes) in this case, i should be/am getting, the recovered clock/64 as 161.13MHz. But what happens if my ref clock is 161.13MHz+100ppm? shouldnt the recovered clock/64 be still 161.13MHz, as the CDR shuld be still tracking 10.3125GHz? From an experiment I did, i observed the recovered clock/64 be around 161.13MHz+100ppm (roughly). I am not sure why this happens. It would be great if any of you kindly help me understand this. Thanks one and all... Best Regards, VEnkat ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu