[SI-LIST] Re: Assessing insertion loss profiles
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 13 Jul 2013 14:45:56 -0700
Both single-ended and differential S parameters provide useful
information. Which to use when has the familiar answer: it depends.
A channel with halves that have ugly single-ended S parameters may yet
still be able to communicate OK as a single channel if the differential
parameters are OK, but will likely present EMC and/or cross-talk problems.
Steve.
On 7/13/2013 10:55 AM, Istvan Nagy wrote:
> Assessing insertion loss profiles
>
> Hi,
>
> Sometimes I have to look at insertion loss profiles (before running a full
> channel simulation with IBIS AMI models) to assess the quality of a channel
> on a PCB.
> Someone says we have to look at the mixed mode Sdd21 for this purpose, but I
> think we should look at the S21 single-ended curve. The PCB-EM simulations
> are done with single ended ports.
> The Sdd21 looks a lot better than the S21, resonances look smaller.
> I think Sdd21 would only be indicative if the channel and the return path
> was perfect without discontinuities.
> I have doubts about the signals being perfectly differential at both TX and
> RX buffers. (for example 10GBASE-KR from an FPGA)
> So, what is the correct approach?
>
> Regards,
> Istvan Nagy
>
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