[SI-LIST] Re: Signal at the driver
- From: Rick Collins <gnuarm.2006@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 17 Sep 2012 14:29:02 -0400
I don't know DDR3, but from your description I would have to assume
that your trace is a typical series terminated driver with an
unterminated receiver. In that case the driver impedance is matched
to the transmission line and so will only drive half way at the
onset. The transition propagates to the receiver where it is
reflected by the high impedance of the termination. The reflected
wave adds to the initial wave bringing the signal voltage to the full
value. Once the reflection reaches the driver the output voltage
should rise to the intended value. The timing of this return wave
will be twice the delay along the transmission line.
If the driver termination does not exactly match the line impedance,
the initial wave will not be half the driver source voltage. The
reflected wave will not add properly and the line voltage at the
driver will not be the same as the driver voltage. This results in
further reflections of diminishing amplitude.
Does this sound like what you are seeing?
Rick
At 12:46 AM 9/17/2012, Shilpa Patil wrote:
>Hi SI Experts,
>I have been carrying out the analysis for DDR3 memory. My query is
>that at the driver end I can see a signal with a dip and shorter
>peak-peak the signal is not a pulse even though I have given a
>pulse, but at the receiver the signal is good. So why is the signal
>at the driver so not a proper pulse?
>
>Regards,
>Shilpa P
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