From: Tadashi ARAI (firstname.lastname@example.org)
Date: Tue Feb 13 2001 - 01:40:31 PST
I met this issue and was confused too, but now it was a legend.
Receiver waveform sometime appears before the driver waveform has reached
to its end of swing. Note that you have observed not only driven
waveform but also reflections. It was reasonable result.
So that you should consider about substitution of reflections from
observed waveform, but it must be difficult.
You can measure the propagation delay instead of the flight time.
To measure propagation delay, you should know the driver delay, in XTK
words "TIME_TO_VM". You can measure it from simulation using a test
fixture, or it was automatically calculated in ibis2xtk.
Prop. delay was measured from when driver waveform reached to
measurement voltage (Vmeas) with test fixture, to the time receiver
waveform reached to Vmeas.
I hope this helps you.
//// /// // / / / / / / / / / /
Tadashi Arai//Platform Developing Dept.,Desktop Prd Div. Fujitsu Limited
email@example.com TEL:+81-42-370-7624 Inagi-shi, Tokyo, Japan
/ / / / / / / / / / / // ///
On Sun, 11 Feb 2001 15:09:16 -0800
Mail from Suchitha.V@smartm.com described as below:
> Hello, All,
> I have a question related to the flight time measurement of GTL+ signals.
> on the FrontSideBus between the Mobile Pentium III processor and the 440BX
> Since the GTL signals are very short and have no termination, there is
> seen at the Chipset end when the Processor is driving.
> I have simulated this in XTK tool, with the processor as driver and the
> chipset as the receiver.
> I have measured the flight time on the rising edge. I have taken the
> impedance to be 55ohms +/- 10% for simulations
> After the processor reaches 1.0 volts or so, at the rising edge, the
> waveform at the processor pin dips, and then rises.
> Therefore after around 1.0 volts, the chipset appears to be leading the
> processor which is wrong.
> Is this happening due to change in impedance? can anyone explain.
> In a case like this, how should the flight time be measured?
> For measurement, should i consider the falling edge including a cycle of
> ringing at the receiver end?
> Can anybody explain?
> looking forward to your replies and suggestions.
> Thanking you
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