Re: [SI-LIST] : LVDS SSO Analysis Question

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From: Jim Freeman (freeman@broadcom.com)
Date: Wed Nov 03 1999 - 11:41:33 PST


Hi david,
    I have simulated LVDS drivers and found that a single power/ground pair per driver was necessary.

Jim Freeman

David Haedge wrote:

> Fellow SIers,
>
> I am working on an SSO analysis that involves large numbers of LVDS outputs
> switching on a die. One of the reasons to use LVDS is because the driver is
> basically just redirecting a 4mA current in the output loop, hopefully
> eliminating large di/dt's on power and ground. However, my SPICE analysis
> shows a 20-25mA current spike on VDD and VSS with a rise/fall time of about
> 230ps each time the device switches (375MHz rate). It was assumed that we
> could get by with a lot less VDD and VSS pads due to the expected low di/dt's.
> It appears now that with this large unexpected current spike, we need to triple
> the number of powers and grounds to achieve an acceptable voltage drop/ground
> bounce. Has anybody out there seen this sort of behavior in LVDS circuitry?
> Or is this just perhaps a quirk in SPICE (or my chosen vendor)?
>
> Anxiously awaiting replies,
>
> David Haedge
> Raytheon
>
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