[SI-LIST] Re: Series termination

Vinayak, may God have mercy on your soul.  If you provide next of kin 
information, family notifications may be arranged.

Seriously, I think you are in a world of trouble here. If you set-up a 
simple simulation, I don't think you will like the results of that funky 
arrangement at 100MHz, much less 150MHz to 3GHz.

If Vdd impedance can't be maintained at the pad, the driver will collapse 
and you can't signal.  You must provide enough low inductance charge store 
to support I/O and shoot through current in the spectrum above the package 
cut-off, which sounds like your entire operating envelope.

If the signal is not referenced properly as a well controlled transmission 
line from the pad through the package an on through the PCB, you will 
likely die below 200MHz, never mind 3GHz.  The actual number will depend on 
a number of factors.

I think you need to get your boss to bring in both an I/O design expert, 
and a package expert to spend some time on this design.  I don't know of 
any cookbook recipes for 6Gbps.

Steve.
At 05:18 PM 12/27/2004 +0530, Vinayak AGRAWAL wrote:
>Hi
>
>I am designing a transceiver that will use series termination. The IO is
>a differential driver, so while one pin will be connected to high
>voltage (external pin) through a series resistor of 50ohms, the other
>will be connected to gnd (and the connectivity switches to toggle the
>output) the same way.
>
>when I started design I thought it should be good enough to terminate in
>this way, because I had seen many single-ended (as opposed to
>differential) drivers doing the same. However now I'm worried whether
>the differential termination will be good enough for a 100ohm termination.
>
>Specifically I'm concerned about the return path for the current. As I
>see it, it is something like: into the negative pin, through 50ohm, gnd,
>gnd-vdd coupling, vdd, 50ohms resistor, positive going pin. I doubt
>whether gnd-vdd coupling will be good enough for high speed data
>transfer (300-6000Mbps). On the other hand I believe similar issues
>should come for single-ended drivers.
>
>Can someone point to any reading material. Also any criticisms of the
>approach are welcome.
>
>Regards
>Vinayak
>
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