Chip with simple program for Toy

[Robert Adsett]

In article <8jd7k.97920$G33.19985@trnddc03>, Talal Itani says...

I have a Tektronix at home, with the 2.k point, and at times it is painful
to use. I see myself trying to scroll and scroll, to see more, and then I
realize that the scope cannot show me more. We are debugging some serial
protocols, so a buffer larger than 2.4 is really needed.

You really want a logic analyser for that rather than an oscilloscope.
You get more triggering options generally and since you only need a
single bit per sample much greater storage depth for the same memory.
You can get combined scope/logic analyzers like the Agilent MSOs

http://www.home.agilent.com/agilent/product.jspx?nid=-35165.536908416.00
&cc=US&lc=eng

that additionally make it easy to trigger digital collection from the
analog channels or vice versa. As an added advantage you can generally
get a number of logic channels for the cost of an analog channels.

Robert
** Posted from http://www.teranews.com **

 

On Jun 21, 12:06 pm, "Talal Itani" <tit...@verizon.net> wrote:

Hello,

I was looking at the schematics for a DSP-based board, running at 100 MHz.
They have a tiny inductor with every bypass cap around the DSP. Do you
think this is necessary? This DSP has analog stuff built-in. If we do not
need analog, can the inductors be eliminated?

Thanks,
T.I.

Is it possible the inductors represent the inductance of the layout,
rather than actual parts on the BOM?

 

On Jun 21, 10:22 am, "Talal Itani" <tit...@verizon.net> wrote:

We are developing a board with a DSP, some logic, and some analog circuitry.
The scope will be used to debug the circuit, make sure signals are clean,
make sure timing is correct. We should get a 4-channel 350 MHz scope, yet

Those are things you need to think about before you even commit to
making a board. The scope won't help you if you do major mistakes in
the design from the start.
You need to simulate stuff before, never mind the scope.

 

[Vladimir Vassilevsky]

Talal Itani wrote:

The DSP is a TI F2808. The schematics I was referring to are here
http://www.ti.com/litv/zip/sprr098. It is a zip file. Once you unzip the
file, 2 pdf files appear. The larger file has the schematics I am referring
to. The inductors are at the top-left corner of the screen.

This mediocre design is obviously made by a superstitious and
unexperienced person. There are several things in the schematics that
should be done differently. No wonder that at some time ago the designer
had burned with the EMC, and after that he sticks the inductors
everywhere. The value of 50uH is ridiculous. Never mind those inductors;
with the sensible layout the F28xx doesn't need them.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[Jim Granville]

Talal Itani wrote:

It is nice if we can do mixed signal, but I am sure we have to pay much
more. We will use this scope in the product development lab, for embedded
work. The signal we are working with is 25MHz digital. Rarely we will look
at a clock of 100 MHz. So, I thought 350 MHz analog is what we should get.
Some Tektronix and LeCroy have a very short buffer. The ones with large
buffer start at $5,000. Is one brand better priced than the others?

Then you may be better with TWO scopes. Get a good, cheap (second hand?)
analog one with as many MHz as you can afford, and then get a Digital
Multi-channel one, with some analog features, but 25MHz digital rates
are not great.
[ie 100MHz-200Mhz Digital/Analog with a 350MHz analog model, is likely
to be cheaper than a 350Mhz bells-and-whistles model.]
Plus, you have TWO instruments, which removes a lab bottle neck.

Use the Analog one once per PCB design to verify clean signals, and the
Digital features you can expect to use during development.

The better digital-leaning ones have more digital channels, and they
can also store EDGES-by-time, rather than have a fixed sample rate.
That means at 25MHz, you can define each edge to 5 or less ns,
and catch rare events.
It is relatively rare these days, to have many digital tracks all over
a PCB - that tends to all swallow into one FPGA+uC, but you can
expect to trouble shoot signals between boards, and things like
protocal margins.

-jg

 

[Joerg]

Talal Itani wrote:

Can ExpressPCB receive files from other PCB software?


I've had good experiences with Advanced Circuits (http://www.
4pcb.com/). Make sure to use their free FDM service
(http://www.freedfm.com/), even if you don't end up going with them for
manufacturing.

ExpressPCB is only good for quick-and-dirty stuff. Their advantage is
that they're cheap and their design software is pretty simple to use,
but the big disadvantage is that it locks you in to their software.
Also I've never done 4-layer stuff with them; I believe they're also
kind of limited in that department. They're great for quick-and-dirty
stuff though.

Regards,
-- Hauke D

On Jun 21, 4:19 pm, "Talal Itani" <tit...@verizon.net> wrote:



Hello,
I need to have a 4-layer board made, a prototype, 2 boards, nothing
fancy.
I did some research in this newsgroup and I narrowed it down to Sierra
Pro
Express, ExpressPCB, and AC Advanced Circuits. ?Do you think I made the
right choice? ?Do you have any recommendations? ?I would like to receive
the
board 3-5 days.
T.I.- Hide quoted text -
- Show quoted text -

I've used ExpressPCB for small projects before, but always 2-layer
stuff.
I've never had a problem with them, or their boards.

As for being "locked-in" to their software, for an extra $60 (last
time I checked), they will send you the Gerber files. From there, you
can import to many of the other programs avail.

Then if you need to make a little change it'll be another $60?

Also, I recall hearing a while ago that a lot of these PCB prototype
houses are all built at the same place anyway. So, while you might
see 10 different company names (i.e., resellers), the boards
themselves all come from the same place. Sorry, I don't remember the
names of the companies involved, and don't know whether ExpressPCB is
one of them.

I have also used 4PCB, quite happy so far. They only messed up once
(unapproved Gerber edits) but made good on that with an additional fast
run, on the house. The nice thing is that I always have a real contact
person there. She really helped us when they defaulted to this dreaded
RoHS process which we absolutely did not want.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

On Jun 21, 4:14 pm, "Talal Itani" <tit...@verizon.net> wrote:

I cannot tell. I do not have BOM. The schematics are here, a zip file
that has 2 PDF files. The large PDF file has the schematics. The inductors
are at the top-left corner of the page. Thanks.

Is it possible the inductors represent the inductance of the layout,
rather than actual parts on the BOM?

That's interesting, the resonance frequency for 100nF with 50uH is
about 21KHz. I wonder what the resonance-decoupling-multi-value caps
crowd has to say about this design?

 

[Joerg]

Talal Itani wrote:

The DSP is a TI F2808. The schematics I was referring to are here
http://www.ti.com/litv/zip/sprr098. It is a zip file. Once you unzip the
file, 2 pdf files appear. The larger file has the schematics I am referring
to. The inductors are at the top-left corner of the screen.

To be honest 50uH and 0.1uF is a recipe for disaster. At the most a
ferrite SMT-bead should be used but usually I don't even do that. A nice
full ground plane and a nice full VCC plane is usually best. Problem
with DSP like this is that you need an additional lower voltage supply
so now you are up to three supply planes, meaning you won't get away
with less than a 6-layer board.

If it's super critical you could have the analog supplies come from a
separate regulator but often converters on a chip with fast digital
processing going on are quite disappointing. A bond wire affords only so
much in RF conductivity.

Hint: Carefully read up on power supply sequencing. Best case wriobng
sequencing leads to a locked up DSP, worst case to a dead DSP.

Oh, and please don't top post.

I was looking at the schematics for a DSP-based board, running at 100 MHz.
They have a tiny inductor with every bypass cap around the DSP. Do you
think this is necessary? This DSP has analog stuff built-in. If we do
not
need analog, can the inductors be eliminated?
Are you sure that these are ordinary inductors or just a wire through
a ferrite bead?

While the ferrite will increase the inductance, a suitable ferrite
material is also quite lossy at higher frequencies, reducing the risk
for unwanted resonances with the capacitors.

Paul

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

Talal Itani wrote:

Ok, maybe not tiny. I have never seen this before, so I wonder whey these
inductors are there.

Possibly a very young guy did the design. There are people who take a
sledgehammer to hang a picture. Sometimes the sledgehammer then makes a
hole in the wall ;-)

BTW, 50uH isn't really "tiny".

For RF it's huge. Like a sledgehammer. Sledgehammers can cause a lot of
grief.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

Tim Wescott wrote:

Talal Itani wrote:
Hello,

I was looking at the schematics for a DSP-based board, running at 100
MHz. They have a tiny inductor with every bypass cap around the DSP.
Do you think this is necessary? This DSP has analog stuff built-in.
If we do not need analog, can the inductors be eliminated?

Thanks,
T.I.

Search for newsgroup postings with "Jeorg" and "ground" or "grounding"
in them.

You'll get a load of (AFAIK) good opinions.

Thanks for the kudos. It would have to be "Joerg" though. Sometimes I
wish I had an easier name.

Inductors in series with the caps would tend to isolate the power supply
from noise in the DSP, but it would also create a bunch of odd
resonances. It's not how I'd want to isolate a power supply from a chip.

It will become really interesting when the DSP exhibits a somewhat
burst-like load behavior. On the scope it'll look like Dolphins
frolicking in the ocean.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

On Jun 21, 12:06 pm, "Talal Itani" <tit...@verizon.net> wrote:

Hello,

I was looking at the schematics for a DSP-based board, running at 100 MHz.
They have a tiny inductor with every bypass cap around the DSP. Do you
think this is necessary? This DSP has analog stuff built-in. If we do not
need analog, can the inductors be eliminated?

Thanks,
T.I.

BTW, 50uH isn't really "tiny".

 

On Jun 22, 5:52 am, Paul Keinanen <keina...@sci.fi> wrote:

On Sat, 21 Jun 2008 16:06:02 GMT, "Talal Itani" <tit...@verizon.net
wrote:

I was looking at the schematics for a DSP-based board, running at 100 MHz.
They have a tiny inductor with every bypass cap around the DSP.  Do you
think this is necessary?  This DSP has analog stuff built-in.  If we do not
need analog, can the inductors be eliminated?

Are you sure that these are ordinary inductors or just a wire through
a ferrite bead?

While the ferrite will increase the inductance, a suitable ferrite
material is also quite lossy at higher frequencies, reducing the risk
for unwanted resonances with the capacitors.

Sadly, you can't rely on this. I've had to put little resistors in
series with ferrite bead to kill a resonance - admittedly at a few
hundred kHz, where the bead doesn't look that lossy.

--
Bill Sloman, Nijmegen

 

[JeffM]

Talal Itani TOP-POSTED:

I am sorry, I did not understand what you are telling me.

People who use Outlook Express to read newsgroups should read this:

http://www.google.com/search?q=cache:I4NVjCO2JKIJ:www.torrens.org.uk/SitePhil/Netiquette.html+*-*-*-*-inferior+published+proper+do.not.properly.mark.quoted.text+top.post+Micro.oft.programs+QUILA+Outlook.Express+official+do-not-*-use-Micro.oft-programs+average+Netiquette+Richard.Torrens+dry+top.posting&strip=1#quila

This page tells you what *you* have to do MANUALLY
to compensate for that TERRIBLE software:
http://www.google.com/search?q=cache:jA9I9kln6pkJ:www.usenet.org.uk/ukpost.html+quoting+proper.attribution+use-a-standard-*-character+outlook.express+*-*-*-before-*-quoted-text+default+Trim+*-a-test-post+move-*-cursor-to-*-bottom-*-*-*-*+unable#ss3.1

Outlook Express has MANY, MANY flaws:
http://groups.google.com/group/sci.electronics.design/browse_frm/thread/a7e801164cadb331/f82cdc06a0dca6b7?q=*-triple-extension-*+easy-to-create+execute-*-code+exploited+Outlook-Express+zzz+*-no-longer-safe-*-*-*-*-*-*-*-*-*+exploit+vulnerabilities+qq-qq+uu+exploiting
http://groups.google.com/group/microsoft.public.windowsxp.general/browse_frm/thread/3e63579968f70adc/3bac48809895403a?q=SUCKS+trivial+get.a.real.news.reader+difficult+poor.design+outlook.express+Other-news-readers-*-*-*+OutlookExpress+OE.users+worth.every.penny
http://groups.google.com/group/comp.lang.python/browse_frm/thread/b4d82899afb75538/88c279033a6828dc?q=zz-zz+*-*-*-real-news-reader+skip.leading.hard.tabs+helping+Outlook.Express&fwc=2
http://groups.google.com/group/alt.support.depression/browse_frm/thread/deabc672d1976c4/b20bb0a866d51d93?q=*-*-*-*-*-*-*-*-*-worse-than-OE+zzz+*-*-*-*-surprised-and-delighted-at-*-*-real-news-readers-*+broken.sig.dash+incapable+Outlook.Express

 

[steve]

On Jun 20, 11:19 pm, "Talal Itani" <tit...@verizon.net> wrote:

Hello,

My boss asked me to evaluate oscilloscopes and to recommend one.  I know
Tektronix and LeCroy.  Which is better?  Are they any others?  Ideally, we
would get a 4-channel scope at 300 MHz, with a 5 million sample record
length.  Thanks for your advise.

T.I.

We have a few very high end LeCroys for deep memories and a bunch of
low end Tek's for everyday work, but they really skip on memory, for
some reason they charge $1000's more for a decent size memory, no one
here likes the Agilent's

 

[CBFalconer]

Talal Itani wrote:

Good idea. Thanks. If my highest-frequency digital signal is 25
MHz, do you think a 100 MHz digital scope is sufficient? What is
a digital-learning scope?

Please do not top-post. You have lost all connection with the
previous articles. Your answer belongs after (or intermixed with)
the quoted material to which you reply, after snipping all
irrelevant material. See the following links:

<http://www.catb.org/~esr/faqs/smart-questions.html>
<http://www.caliburn.nl/topposting.html>
<http://www.netmeister.org/news/learn2quote.html>
<http://cfaj.freeshell.org/google/> (taming google)

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.


** Posted from http://www.teranews.com **

 

[steve]

On Jun 21, 5:16 am, "Talal Itani" <tit...@verizon.net> wrote:

Hello,

My company wants to buy an oscilloscope.  The scope that meets our needs is
around $7,000.  I am sure we can save much money if we buy a PC-based unit,
like Picoscope.  Do you have experience with PC based scopes?  Do you
recommend them for serious work?

Thanks

They just aren't convenient, ideally, you want something small so it
can easily be moved from lab to lab to thermal chamber etc. battery
powered is even better.

 

[Tim Wescott]

Joerg wrote:

Tim Wescott wrote:
Talal Itani wrote:
Hello,

I was looking at the schematics for a DSP-based board, running at 100
MHz. They have a tiny inductor with every bypass cap around the DSP.
Do you think this is necessary? This DSP has analog stuff built-in.
If we do not need analog, can the inductors be eliminated?

Thanks,
T.I.

Search for newsgroup postings with "Jeorg" and "ground" or "grounding"
in them.

You'll get a load of (AFAIK) good opinions.


Thanks for the kudos. It would have to be "Joerg" though. Sometimes I
wish I had an easier name.

'O' before 'E' unless I'm at sea?

Dunno why I can't keep it straight.

Inductors in series with the caps would tend to isolate the power
supply from noise in the DSP, but it would also create a bunch of odd
resonances. It's not how I'd want to isolate a power supply from a chip.


It will become really interesting when the DSP exhibits a somewhat
burst-like load behavior. On the scope it'll look like Dolphins
frolicking in the ocean.

That's kinda what I thought. Plus I see no reason to do each power line

individually, and some good reasons not to (Different versions of VDD at
different points in the circuit, oh boy!).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Tim Wescott]

Joerg wrote:

Talal Itani wrote:
Ok, maybe not tiny. I have never seen this before, so I wonder whey
these inductors are there.


Possibly a very young guy did the design. There are people who take a
sledgehammer to hang a picture. Sometimes the sledgehammer then makes a
hole in the wall ;-)


BTW, 50uH isn't really "tiny".


For RF it's huge. Like a sledgehammer. Sledgehammers can cause a lot of
grief.

WHAT? You mean that semiconductor companies hire kids with no real

experience fresh out of college to be applications engineers?

Now THAT would imply that they look at their applications engineers as a
marketing expense, not a profit center.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Jim Thompson]

On Sat, 21 Jun 2008 18:48:53 -0700, Tim Wescott <tim@seemywebsite.com>
wrote:

Joerg wrote:
Talal Itani wrote:
Ok, maybe not tiny. I have never seen this before, so I wonder whey
these inductors are there.


Possibly a very young guy did the design. There are people who take a
sledgehammer to hang a picture. Sometimes the sledgehammer then makes a
hole in the wall ;-)


BTW, 50uH isn't really "tiny".


For RF it's huge. Like a sledgehammer. Sledgehammers can cause a lot of
grief.

WHAT? You mean that semiconductor companies hire kids with no real
experience fresh out of college to be applications engineers?

Now THAT would imply that they look at their applications engineers as a
marketing expense, not a profit center.

Naaaaaah! Can that be ?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
| |
| America: Land of the Free, Because of the Brave |
| |
| Due to excessive spam, googlegroups, UAR & AIOE are blocked! |

 

[Jim Granville]

Talal Itani wrote:

Then you may be better with TWO scopes. Get a good, cheap (second hand?)
analog one with as many MHz as you can afford, and then get a Digital
Multi-channel one, with some analog features, but 25MHz digital rates are
not great.
[ie 100MHz-200Mhz Digital/Analog with a 350MHz analog model, is likely
to be cheaper than a 350Mhz bells-and-whistles model.]
Plus, you have TWO instruments, which removes a lab bottle neck.

Use the Analog one once per PCB design to verify clean signals, and the
Digital features you can expect to use during development.

The better digital-leaning ones have more digital channels, and they
can also store EDGES-by-time, rather than have a fixed sample rate.
That means at 25MHz, you can define each edge to 5 or less ns,
and catch rare events.
It is relatively rare these days, to have many digital tracks all over
a PCB - that tends to all swallow into one FPGA+uC, but you can
expect to trouble shoot signals between boards, and things like
protocal margins.

Good idea. Thanks. If my highest-frequency digital signal is 25 MHz, do
you think a 100 MHz digital scope is sufficient?

I'd see if you can find a 100msps+ Analog, with 200Msps+ Digital (5ns),
that should be at the 'bottom end', as that's quite do-able with
mainstream FPGA and ADC parts.

The Digital Model can also be a PC based one (it's all pixels), whilst
the analog model, clearly is not.

What is a digital-learning scope?
Not digtal-learning, but Digital-leaning

That means one with more 'leaning' towards the digital features.
Edge storage I would classify as Digital-Leaning, as
would good Frequency and Phase resolution.
Some have protocol-extraction software.

As an example, this is one I use :
http://www.cleverscope.com/

[- but the edge-storage feature is still coming as SW upgrade...]

-jg