# [SI-LIST] Re: Maximum frequency consideration for high-speed digital analysis of differential signals

• From: <art_porter@xxxxxxxxxxx>
• To: <Cortex.Chen@xxxxxxxxxxxx>, <tom@xxxxxxxxxxxxx>, <rula.bakleh@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
• Date: Fri, 6 Jan 2006 09:17:44 -0700

```Well it all depends on the shape of the filter response. Is it =
single-pole RC? 3rd-order Chebyshev? Gaussian? The ratios listed below =
are true for Gaussian but not necessarily for all responses. For =
instance, for today's more brick-wall-like scope responses, the 10-90 =
numerator is closer to 0.42.  =20

Art Porter
Agilent=20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Cortex.Chen@xxxxxxxxxxxx
Sent: Thursday, January 05, 2006 7:26 PM
To: tom@xxxxxxxxxxxxx; rula.bakleh@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Maximum frequency consideration for high-speed =
digital analysis of differential signals

0.35/Tr ---- 10% to 90%
0.22/Tr ---- 20% to 80%
=20
Regards,
=20
Cortex
________________________________

From: si-list-bounce@xxxxxxxxxxxxx =A5N=B2z Tom Dagostino
To: rula.bakleh@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Maximum frequency consideration for high-speed =
digital analysis of differential signals

I'm not sure how you are computing your bandwidth.  If you have a 25 =
psec
risetime (assuming 10-90%) your -3dB bandwidth is 0.35/25psec or 14 GHz.

When analyzing bandwidth requirements for systems like this most people =
talk
about passing the 3rd or 5th harmonic of the clock.  In your case that =
is
7.5 or 12.5 GHz.  Some analysis of your system requirements is in order.

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of rula.bakleh@xxxxxxxxxx
Sent: Thursday, January 05, 2006 2:19 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Maximum frequency consideration for high-speed
digital analysis of differential signals

Hi Everyone,

I'm designing a differential signal for the Rocket I/O interface. My =
signal
speed is 5 Gbit/sec, operating frequency is 2.5 GHz, and fastest edge =
rate
is 25 psec or 40 GHz.

In regards to performing channel analysis, what is the highest frequency
content to consider when designing this particular differential signal
serial link?  If I am measuring or simulating S parameters for various
portions of this link what is the highest frequency of interest that I =
need
to consider as a rule of thumb and why?

Is it the operating frequency only, multiples/harmonics of the operating
freq, edge rate frequency (f=3D1/trise), multiples/harmonics of the edge =
rate
freq, or some fraction of the edge rate?  I'm finding conflicting
information: some people say that it's the full edge rate, others say =
0.35
or 0.5 of the edge rate, and yet others say multiples of the edge =
frequency
should be taken into account for analysis and design.  I'm hoping that
somebody could shed some light on this topic for me.

Thank You,

Rula Bakleh

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