[SI-LIST] Re: Maximum frequency consideration for high-speed digital analysis of differential signals
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Fri, 06 Jan 2006 14:55:18 -0500
Brett corrected me.
What I meant to say was 3X the highest fundamental frequency, which for
a 10G links is 5 GHz.
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
Scott McMorrow wrote:
>Just to throw something out there ....
>
>I contend that BW is not the most interesting specification to be
>concerned about for serial links. BW only tells part of the story. The
>other half is told by the phase response (or group delay). I generally
>like to perform simulation and modeling at a minimum of 3X the Nyquist
>frequency for the data stream, in order to accurately capture phase
>information. For 10G NRZ links, that would require a 15 GHz bandwidth
>in all modeling and simulation.
>
>regards,
>
>Scott
>
>Scott McMorrow
>Teraspeed Consulting Group LLC
>121 North River Drive
>Narragansett, RI 02882
>(401) 284-1827 Business
>(401) 284-1840 Fax
>
>http://www.teraspeed.com
>
>Teraspeed® is the registered service mark of
>Teraspeed Consulting Group LLC
>
>
>
>Grossman, Brett wrote:
>
>
>
>>Wow, if I had a dime for every time this question came up...
>>
>>I had attended a seminar at DesignCon a few years back when I was
>>struggling with this same question on the 40Gb/s interconnects we were
>>designing. The instructor (Henri Merkelo) asked a question of the
>>audience as to the necessary bandwidth for a 10Gb/s. From an audience
>>of folks with collectively dozens of products already shipping in the
>>10Gb/s space, there were plenty of different answers. Here is a
>>sampling.
>>
>>1. BW=3D0.35/tr(10-90)
>>2. BW=3D0.22/tr(20-80)
>>3. f0=3D0.5*datarate, then BW=3D3*f0
>>4. or BW=3D5*f0
>>5. or BW=3D10*f0 (i.e. odd harmonics of the fundamental)
>>6. f0=3D0.5*datarate or 1.0*datarate depending on the coding scheme (for
>>example RZ vs. NRZ)=20
>>7. BW =3D datarate / 2*log2(number of encoded symbols)
>>8. Enough bandwidth such that when passed through a brick-wall (or
>>n-pole) filter the residual power spectral density of enough bits of a
>>PRBS, is small enough.
>>
>>There are lots more, but I'll save the rest (along with the truth about
>>the steroid abuse and wild parties of SI engineers) till I right my
>>'tell all' book of the signal integrity world ;^) =20
>>
>>In reality, I think you will be hard pressed to find a rule of thumb
>>that satisfies all your needs. All those that have been mentioned by
>>myself and others are a good start to help better understand the 'big
>>knobs' in your system. The cost of trying these different approaches
>>and evaluating the sensitivity of your system to the different choices
>>can be pretty reasonable in a simulation environment. BTW, my response
>>is intended to be very general and not specific to the Rocket I/O
>>interface. For that interface some industry standard or customer
>>reference designs may exist, but I am sorry that I haven't worked with
>>it before. Maybe some of the Xilinx folks will have more input.
>>
>>My $0.02,
>>-Brett
>>
>>-----Original Message-----
>>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>On Behalf Of art_porter@xxxxxxxxxxx
>>Sent: Friday, January 06, 2006 8:18 AM
>>To: Cortex.Chen@xxxxxxxxxxxx; tom@xxxxxxxxxxxxx; rula.bakleh@xxxxxxxxxx;
>>si-list@xxxxxxxxxxxxx
>>Subject: [SI-LIST] Re: Maximum frequency consideration for high-speed
>>digital analysis of differential signals
>>
>>Well it all depends on the shape of the filter response. Is it =3D
>>single-pole RC? 3rd-order Chebyshev? Gaussian? The ratios listed below =
>>=3D
>>are true for Gaussian but not necessarily for all responses. For =3D
>>instance, for today's more brick-wall-like scope responses, the 10-90 =
>>=3D
>>numerator is closer to 0.42. =3D20
>>
>>Art Porter
>>Agilent=3D20
>>
>>-----Original Message-----
>>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>=3D
>>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 =
>>=3D
>>digital analysis of differential signals
>>
>>0.35/Tr ---- 10% to 90%
>>0.22/Tr ---- 20% to 80%
>>=3D20
>>Regards,
>>=3D20
>>Cortex
>>________________________________
>>
>>From: si-list-bounce@xxxxxxxxxxxxx =3DA5N=3DB2z Tom Dagostino
>>Sent: 2006/1/6 [=3DACP=3DB4=3DC1=3DA4=3DAD] =3DA4W=3DA4=3DC8 10:03
>>To: rula.bakleh@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
>>Subject: [SI-LIST] Re: Maximum frequency consideration for high-speed =
>>=3D
>>digital analysis of differential signals
>>
>>
>>
>>I'm not sure how you are computing your bandwidth. If you have a 25 =3D
>>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
>>=3D
>>talk
>>about passing the 3rd or 5th harmonic of the clock. In your case that =
>>=3D
>>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 =3D
>>signal
>>speed is 5 Gbit/sec, operating frequency is 2.5 GHz, and fastest edge =
>>=3D
>>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 =
>>=3D
>>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=3D3D1/trise), multiples/harmonics of the =
>>edge
>>=3D
>>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 =
>>=3D
>>0.35
>>or 0.5 of the edge rate, and yet others say multiples of the edge =3D
>>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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