[SI-LIST] Re: 2.5Gbps
- From: Dorin <dorin.oprea@xxxxxxxxxxx>
- To: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
- Date: Mon, 21 Jul 2003 11:13:31 -0400
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Hi Patrick,
Thanks for you reply. Can we go through an example?
1) We have BER=10e-6; thus,
Poe=0.5*(1-erf)*sqrt(Eb/No)
I need to take a value for erf, error function, to get Eb/No =>
erf=?
Eb= energy in one bit
No= noise power density
=> Eb/No
2) S/N=(Eb/No)*R/W
N=0.05V
S= wanted unknown
R=2.5Gb/s
W= signal energy sent into the line; suppose W=20mW
=> S
3) S=0.1+Smargin
0.1V is the signal threshold
=> Smargin which is the requested value
Is it correct? How do I determine erf?
Best regards,
Dorin
"Zabinski, Patrick J." wrote:
> Dorin,
>
> The answer will come down to the target bit error rate your
> shooting for with the link. From that, you can determine
> the signal to noise ratio, which will lead you to some
> specs for the signal strength.
>
> There is literature on the web and in text to get you going,
> but I suggest you start with the basics on bit error rate
> analysis related to signal to noise ratio. This will give
> you a good idea how they relate and how you can eventually
> derermine the signal margin you want.
>
> As an example (not necessarily applicable to your situation),
> you might determine a bit error rate (BER) of 10^-12 is
> sufficient for your link. From that, you can determine a
> signal to noise ratio (SNR) of 7:1 is required.
>
> You'll then have to determine or estimate your effective RMS
> noise on your link. For typical links, 40-50 mV of RMS noise
> is a reasonable guess, which will then determine that you
> need a 280-350 mV opening within the eye diagram (note: 280-350
> mV opening from threshold to inside portion of eye).
>
> Again, this is an example that is not specifically related to
> your application, so you'll want to perform your own analysis.
> Also, I highly recommend you read up on the topic of BER
> vs SNR, as it will help you with some of the basics and
> the not-so-basic issues.
>
> Hope this helps,
> Pat
>
> > Hi,
> > There is a 2.5Gbps system link through the back plane with an
> > interconnect length of 35".
> > What should be the simulated voltage level for a receiver with 100mV
> > threshold so that one can be confident in his design?
> > Is it 200mV (2*100mV) sufficient? What is preferred value?
> > How much jitter on the simulated eye is accepted?
> >
> > Thanks,
> > Dorin
> >
> >
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