Interfacing to S4/S3 LVDS

[Altera_Forum]

Hi All, 

 I would like to interface an ADC that has a Vocm of 820mV at 780Mbps to the S4 LVDS receiver. The S4 data sheet has the Vicm at:   0.05V < VICM < 1.8V for Dmax less than 700Mbps and 1.05V < VICM < 1.55V for Dmax greater than 700Mbps   How best to connect the two devices?   For comparison, I looked at the Virtex6 LVDS and it has Vicm at: 0.3V < VICM < 2.2V with no separate rows based on Dmax.    Thanks, DannyK

[Altera_Forum]

What's the involved ADC type? The Vocm specification seems surprizing, because it doesn't meet the general LVDS specification. Strictly spoken, it shouldn't be designated LVDS. Depending on the transmitter and signal characteristic, there should be ways to perform a level shifting. At wost case, LVDS repeaters can be used.

[Altera_Forum]

My personal feeling is that you won't have any issues if you just directly connect the two together (dc coupled).  

 However, if you're concerned:  My first suggestion would be to use an LVDS buffer from either Micrel or On semi: http://www.onsemi.com/pub/collateral/nb4n527s-d.pdf http://www.micrel.com/_pdf/hbw/sy58605u.pdf  My second suggestion would be to use an AC coupling scheme with DC bias. This document might be helpful: http://focus.ti.com/lit/an/scaa059c/scaa059c.pdf  Jake

[Altera_Forum]

AC coupling is the most simple way, but is only permitted for DC balanced data, e.g. 8b/10b or manchester encoded. ADC data most likely aren't of this type. But I would prefer to know about the transmitter characteristics before making detail suggestions.