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Re: Single ended XGMII


I would also vote for single ended SSTL_2 or HSTL for XGMII.  Currently all 
SerDes HSPI compliant are SSTL_2 which operate at 250 Mb/s.  As we move up in 
the speed 500-1000 Mb/s we need to consider HSTL or STTL_1 (does not exist).  
However if you scale the SSTL2 levels to 1.5 volts you will get HSTL levels.


Ali Ghiasi
Sun Microsystems

> From: Curt Berg <cberg@xxxxxxxxxxxxxxxxxxx>
> To: HSSG <stds-802-3-hssg@xxxxxxxx>
> Subject: Single ended XGMII
> Date: Fri, 24 Mar 2000 05:10:42 -0800
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> A few comments on using a single ended XGMII:
> - Today we have several Quad SERDES chips in production, operating
>   at 1.25/2.5 Gbit/s with 8B or 10B interfaces. Most 
>   use a 3.3V I/O swing, and I would guess about 40 ohm (nominal)
>   LVTTL/LVCMOS drivers. This effectively is a 32 bit interface.
>   I would say, these devices seem to function well for many companies.
> - Some vendors are event moving to higher integration then
>   Quads, still using single ended interface. This further indicates
>   that noise is not a major problem.
> - Single ended interface on the MAC side is not an issue. There
>   are many ASIC in production today with 400+ single ended I/Os,
>   and board with several tens of thousands of single ended nets.
> - If we for XGMII use a (1.5 V swing) HSTL instead, and
>   move to a 50-55 ohm impedance controlled driver, we should be 
>   able reduce the effective noise levels by close to a factor 
>   of three.
> My conclusion is that the industry keeps pushing the 
> capabilities of single ended interfaces, just because
> differential interfaces double this pincount.
> If we can reduce the noise by a factor of 3, and not
> move up much in frequency, from existing proven solutions,
> I believe we have a workable solution.
> -Curt Berg-