[SI-LIST] Re: high speed test measurement equipment?
- From: "Douglas C. Smith" <doug@xxxxxxxxxx>
- To: louis.sanchez@xxxxxxxxx
- Date: Wed, 06 Feb 2002 12:19:54 -0800
Hi Louis,
It should be pointed out that probe risetime as seen in your circuit may
have nothing to do with its specification! Probes are usually specified
with a 50 Ohm source and then used in an environment that is not 50
Ohms. EMI filters and some immunity test equipment it treated the same
way leading to problems there as well. Another result of such a
specification is that you can not generally use a probe anywhere near
its stated bandwidth because the probe input impedance near the
bandwidth spec is usually comparable to 50 Ohms! The result is to slow
down the risetime charging up the probe capacitance. The resulting
circuit loading can have a significant effect on the waveform in the
circuit being probed.
Doug
"Sanchez, Louis" wrote:
>
> Scope bandwidth required, is also based on how much error you are willing to
> accept when measuring the rise time on the scope. Using a factor of either 3
> or 5 is a good rule of thumb. The rise time observed on the scope is the
> root sum square of the scope rise time, probe rise time, and the rise time
> of the waveform under observation. Given a permissable % or error in
> measured risetime, and a particular probes risetime, then the root sum
> square relationship can be massaged to yield the minimum scope bandwidth. I
> have used a Mathcad worksheet to graph percentage of error as a function of
> scope bandwidth. This proved useful in helping us to evaluate our
> requirements prior to purchasing.
>
> Although the relationship between the bandwidth of a scope and its
> equivalent risetime is expressed by BW=.35/risetime for a 10% to 90%
> measurement, the rise time of many high frequency signals are measured from
> the 20% to 80% points on the waveform, e.g., LVDS and PECL. Using a single
> pole response model, the relationship between bandwidth and risetime becomes
> approximately: BW=.22/risetime. I mention this because I think its important
> to consider whether the risetime of a pulse is measured using the 10%/90%
> method or the 20%/80% method. Particularly if you're performing any analysis
> that reduces everything to an equivalent bandwidth.
>
> -----Original Message-----
> From: Dagostino, Tom [mailto:tom_dagostino@xxxxxxxxxxx]
> Sent: Wednesday, February 06, 2002 9:31 AM
> To: 'jvalle@xxxxxxxxxxxxxxxxxxxxxx'; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: high speed test measurement equipment?
>
> Scope bandwidth required is determine by the fastest risetime you need to
> observe, look at the IBIS models or SPICE models you have. Compute the
> bandwidth of that risetime (falltime). For a risetime expressed from 10 to
> 90% use the equation BW = .35/risetime. For example a 350 psec risetime
> yields a 1 GHz bandwidth. To properly display this risetime you will need 3
> to 5 times the bandwidth in the scope and probe system. So you need to look
> at the bandwidth at the probe tip. Remember to keep your probe's ground
> lead as short as possible. The scope probe should have minimum loading on
> the circuit, less than 1 pF.
>
> It is impossible for an outsider to tell you what you need. You need to
> look at what signals you are exploring. Rise/fall times for modern
> component range from about 1 nsec to 15 psec which result in bandwidth
> requirements from over 1 GHz to way over 30.
>
> Tom Dagostino
> Modeling Manager
> Mentor Graphics Corp.
> SAS
> tom_dagostino@xxxxxxxxxx
> 503-685-1613
>
> -----Original Message-----
> From: Javier del Valle [mailto:jvalle@xxxxxxxxxxxxxxxxxxxxxx]
> Sent: Tuesday, February 05, 2002 11:27 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: high speed test measurement equipment?
>
> Thanks for the info but, could someone also tell me which test equipment
> models they use for signal integrity?. I mean the oscilloscope should have
> 500Mhz, 1GHz bandwith or more, and also is it needed a special probes for
> signal integrity measurements?.
>
> Thanks a lot again,
>
> Javi
>
>
> -----Mensaje original-----
> De: Bob Patel [mailto:whizplayer@xxxxxxxxx]
> Enviado el: martes 5 de febrero de 2002 19:22
> Para: jvalle@xxxxxxxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Asunto: Re: [SI-LIST] high speed test measurement equipment?
>
> Hi! JAvier,
> Books: 1) High speed digital design- A handbook of
> Black magic by Howard Johnson
> 2)High Speed Digital System Design: Hall Hall McCall
> Web sites: 1)www.sigcon.com
> 2)www.ultracad.com
> 3)www.dsmith.org
> Equipment: I prefer a VNA with built in TDR, this way
> you can do both frequency domain & time doamin
> measurements--Contact Agilent
> Bob
> --- Javier del Valle <jvalle@xxxxxxxxxxxxxxxxxxxxxx>
> wrote:
> >
> > Hi to all,
> >
> > I am quite junior at high speed/signal integrity
> > design and I would like to
> > learn more about it. I have seen some demos of
> > programmes like Specctraquest
> > and hyperlinx, that some of you use for your
> > designs. I would like to know
> > also which is the test and measurement equipment
> > needed, and the required
> > specifications of these equipment for the design of
> > boards similar to PC
> > motherboards that integrates microprocessors like
> > Pentium IV, PowerPC with
> > high speed buses. I also would appreciate if someone
> > could recommend me some
> > books for learning about how to perform high speed
> > measurements, what to
> > measure (timing measurements, ...) etc. (I just have
> > read a book about this
> > field but was not much practical).
> >
> > Thanks a lot and best regards,
> >
> > Javi
> >
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