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https://designers-guide.org/forum/YaBB.pl Design >> High-Speed I/O Design >> AC Coupling cap with different values https://designers-guide.org/forum/YaBB.pl?num=1343888766 Message started by casual on Aug 1st, 2012, 11:26pm |
Title: AC Coupling cap with different values Post by casual on Aug 1st, 2012, 11:26pm Hi I tested 5Gbps Tx driver with different ac coupling cap value, 4pF & 100nF with 100ohm differential termination. The waveforms are as below: When the ac coupling cap is 100nF, the differential signals are shifted, is it normal or something wrong?? for PCIe2 , the coupling cap is around 65-200nF right? |
Title: Re: AC Coupling cap with different values Post by loose-electron on Aug 26th, 2012, 1:11pm They are phase shifted in both cases. Basic network theory - Whats the impedance you are coupling into? |
Title: Re: AC Coupling cap with different values Post by casual on Aug 26th, 2012, 8:06pm i know the reason already. it is due to the initial simulation condition, where the nodes are not settle down yet. |
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