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Messages from 9500

Article: 9500
Subject: Re: Linux and Xchecker
From: Uwe Bonnes <bon@elektron.ikp.physik.tu-darmstadt.de>
Date: 19 Mar 1998 08:52:26 GMT
Links: << >>  << T >>  << A >>
keiser anthony lynn <akeiser@ews.uiuc.edu> wrote:
:   Greetings,

:   I am trying to make an xchecker download program to run on Linux.
: I have found the schematics on Xilinx's web page, but can find no
: information on any of the "commands" that are obviously being stored
: in the XC3042 and/or SRAM.  Any help you can provide would be 
: appreciated.

Hallo,

I don't know what system the original program runs on, but I guess either
Dos or win. If these commands are doenloaded via either the serial or
parallel port, dosemu or wine might be good programms to spy what is going
on on these ports.

Bye 
-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
Article: 9501
Subject: Re: Linux and Xchecker
From: Thomas Sailer <sailer@ife.ee.ethz.ch>
Date: Thu, 19 Mar 1998 11:23:27 +0100
Links: << >>  << T >>  << A >>
Uwe Bonnes wrote:
> 
> keiser anthony lynn <akeiser@ews.uiuc.edu> wrote:
> :   I am trying to make an xchecker download program to run on Linux.
> : I have found the schematics on Xilinx's web page, but can find no
> : information on any of the "commands" that are obviously being stored
> : in the XC3042 and/or SRAM.  Any help you can provide would be
> : appreciated.

Depends on what you want to do, but maybe you can use Xilinx's
parallel cable, which consists only of two 74HC125 and therefore
should be easy to figure out.

> I don't know what system the original program runs on, but I guess either
> Dos or win. If these commands are doenloaded via either the serial or

And Solaris - sort of.

Tom
Article: 9502
Subject: Looking for space qualified FPGAs/ASICs
From: "Stephen King" <sking@crl.co.uk>
Date: 19 Mar 98 10:45:09 GMT
Links: << >>  << T >>  << A >>
We are looking to encode a complicated algorithm onto either an FPGA or
ASIC for space applications.

We are interested to know of any space qualified:

1.) FPGAs,

2.) Low volume ASIC processes (e.g. laser programmable, shared wafer etc),

3.) Conventional ASIC processes.

Thanks for you help in this matter.

-- 
Stephen King
CRL
sking@crl.co.uk
Article: 9503
Subject: Re: Looking for space qualified FPGAs/ASICs
From: Randy Tietz <rrtietz@cca.rockwell.com>
Date: Thu, 19 Mar 1998 08:09:57 -0600
Links: << >>  << T >>  << A >>
Stephen King wrote:
> 
> We are looking to encode a complicated algorithm onto either an FPGA or
> ASIC for space applications.
> 
> We are interested to know of any space qualified:
> 
> 1.) FPGAs,
>
  Might want to look at RH1280 from Actel (http://www.actel.com)
> 
> 2.) Low volume ASIC processes (e.g. laser programmable, shared wafer etc),
>
  One possibility is UTMC rad hard gate arrays (http://www.utmc.com)
> 
> 3.) Conventional ASIC processes.
> 
> Thanks for you help in this matter.
> 

Randy
Article: 9504
Subject: Re: Strange Xilinx question?
From: acher@informatik.tu-muenchen.de (Georg Acher)
Date: 19 Mar 1998 14:53:19 GMT
Links: << >>  << T >>  << A >>

In article <Eq0zI6.J3H@world.std.com>, jhallen@world.std.com (Joseph H Allen) writes:
..<del>..
|> I think what he wants is to take all of the possible bitstreams for his
|> application (each generated with XDE), XOR them together and store the
|> differences from a "master" one.  It would be a kind of compression...

I did such a compression. Due to a tight timing, I've implemented the address 
decoders for a DRAM controller (using a 3042A) without the possibility of in 
system reconfiguration (without RAM (like XC4000), this would mean a lot of 
wasted FFs).
Because there were various decoding schemes, I got tired of changing the 
decoder in the schematic and guided routing. I've then locked the 
decoder CLBs to fixed locations, and compared the bitstreams. 'diff' is a very
useful tool ;-) So I've figured out the LUT-position for about 10 CLBs. Now 
there's only one 'master' bitstream plus various patch informations. Before 
downloading, this information is analyzed and patched into the bitstream...

|> Someone should write a program to automate this process...  I.E., it would
|> generate a test design, run makebits and store the xor difference between
|> the result and a blank design.  This would probably get you pretty close to
|> a reverse engineered bit-stream format.  Then you just need to adapt a few
|> of those berkeley tools, and voila, a freeware xilinx design system :-)

Any volunteers? ;-)


-- 
	Bye
         Georg Acher, acher@informatik.tu-muenchen.de         
         http://www.informatik.tu-muenchen.de/~acher/
          "Oh no, not again !" The bowl of petunias          
Article: 9505
Subject: Re: Looking for space qualified FPGAs/ASICs
From: Ray Andraka <no_spam_randraka@ids.net>
Date: Thu, 19 Mar 1998 12:17:26 -0500
Links: << >>  << T >>  << A >>
Stephen King wrote:
> 
> We are looking to encode a complicated algorithm onto either an FPGA or
> ASIC for space applications.
> 
> We are interested to know of any space qualified:
> 
> 1.) FPGAs,
> 
> 2.) Low volume ASIC processes (e.g. laser programmable, shared wafer etc),
> 
> 3.) Conventional ASIC processes.
> 
> Thanks for you help in this matter.
> 
> --
> Stephen King
> CRL
> sking@crl.co.uk

For FPGAs, Actel has a hardened line, I think they are in the 1280
family.  A few years ago harris was working on a rad hard device too,
but I don't know if it ever came to market.
Article: 9506
Subject: Re: Strange Xilinx question?
From: David Pashley <david@fpga.demon.co.uk>
Date: Thu, 19 Mar 1998 18:10:23 +0000
Links: << >>  << T >>  << A >>
In article <350D75C6.D51B486D@xilinx.com>, Peter Alfke
<peter.alfke@xilinx.com> writes
<snip>
>Somebody mentioned reverse engineering. Obviously, NeoCAD did it.
>But remember that they were ( are ) a bunch of very experienced
>engineers, and they spent a few dozen man-years ( "person-years" to be
>politically correct ) on their software effort. And they found out that
>it is not a viable stand-alone business.

Er, how do you deduce that it wasn't a viable stand-alone business? 

Surely that Xilinx had to pay (it has been claimed) nearly $20m for
NeoCAD, and that both Xilinx and Lucent are still using the technology
(which also supported Actel and Motorola, with Altera "in the works") is
evidence of the viability of the business?

>
>So, if you have the time and a few million dollars, and nothing better
>to do,  you can do it. Otherwise it's much cheaper to buy the software..
>
And incidentally, you can't try a P&R of your design in other vendors'
FPGAs like you could with NeoCAD. 

--
David Pashley
Article: 9507
Subject: Re: Strange Xilinx question?
From: Peter Alfke <peter.alfke@xilinx.com>
Date: Thu, 19 Mar 1998 10:42:44 -0800
Links: << >>  << T >>  << A >>
Let me just repeat:
Xilinx has no interest in making ( or keeping ) the position of
LUT-defining bits a deep mystery.
Go ahead and create any neat editor, but you should also assume that you
can get the bit positions from us for free and without hassle.

Peter Alfke, Xilinx Applications  

Article: 9508
Subject: Re: Strange Xilinx question?
From: Peter Alfke <peter.alfke@xilinx.com>
Date: Thu, 19 Mar 1998 10:43:04 -0800
Links: << >>  << T >>  << A >>
Let me just repeat:
Xilinx has no interest in making ( or keeping ) the position of
LUT-defining bits a deep mystery.
Go ahead and create any neat editor, but you should also assume that you
can get the bit positions from us for free and without hassle.

Peter Alfke, Xilinx Applications  

Article: 9509
Subject: Re: Strange Xilinx question?
From: gah@u.washington.edu (G. Herrmannsfeldt)
Date: 20 Mar 1998 00:06:40 GMT
Links: << >>  << T >>  << A >>

How about the carry logic bits, which my design also required?

-- glen


Peter Alfke <peter.alfke@xilinx.com> writes:

>Let me just repeat:
>Xilinx has no interest in making ( or keeping ) the position of
>LUT-defining bits a deep mystery.
>Go ahead and create any neat editor, but you should also assume that you
>can get the bit positions from us for free and without hassle.

>Peter Alfke, Xilinx Applications  

Article: 9510
Subject: Re: Ideas for an FPGA Project?
From: graeme@wallaby.digideas.com.au (Graeme Gill)
Date: 20 Mar 1998 11:18:43 +1100
Links: << >>  << T >>  << A >>
Guitar Man (abuse@erols.com) wrote:
: Something I have wanted to do for a long time is to make a pulse width
: modulated analog output from a digital signal. For this you will need a
: very high speed clock. 100 MHz is not too high. The samples that you
[snip]
: The limitation of this design is that you need an extremely high speed
: clock to reach the upper limit of human hearing with reasonable dynamic
: range. For example, 16 bits require 65536 clock pulses per sample X
: 40,000 sample per second = 2,560,000,000 Hz or 2.5 GHz clock speed. But
: at telephone quality, 12 bits, 4,096 x 8,000 = 32,000,000 Hz or 32 MHz.
: This is within the range of an FPGA.

Check out how a modern 1 bit D/A convert works. (ie. www.crystal.com)
It gets away with a much lower clock signal that above by spreading
the "on" and "off" periods in a noise shaped way amongst the available
clock periods.

Graeme Gill.
Article: 9511
Subject: Re: Looking for space qualified FPGAs/ASICs
From: dmb00000@erols.com (Dave Bancroft)
Date: 20 Mar 1998 01:19:03 GMT
Links: << >>  << T >>  << A >>
In article <01bd5324$d36ff5e0$1d3872c1@sk_ii.crl.co.uk>, sking@crl.co.uk 
says...
>
>We are looking to encode a complicated algorithm onto either an FPGA or
>ASIC for space applications.
>
>We are interested to know of any space qualified:
>
>1.) FPGAs,

Actel puts out two, the RH1020 and RH1280.  

>
>2.) Low volume ASIC processes (e.g. laser programmable, shared wafer etc),
>
>3.) Conventional ASIC processes.
>

Honeywell has a series of SOI/SOS gate array Asics.  You can check them out at 
www.ssec.honeywell.com  UTMC also has gate array Asics, but I don't think they 
are nearly as radhard as the Honeywell's.  If you're into full custom Asics, 
Harris, Hughes and Raytheon have foundries.  



Article: 9512
Subject: Re: Ideas for an FPGA Project?
From: Guitar Man <abuse@erols.com>
Date: Thu, 19 Mar 1998 22:35:09 -0500
Links: << >>  << T >>  << A >>
Graeme Gill wrote:

> Guitar Man (abuse@erols.com) wrote:
> : Something I have wanted to do for a long time is to make a pulse width
> : modulated analog output from a digital signal. For this you will need a
> : very high speed clock. 100 MHz is not too high. The samples that you
> [snip]
> : The limitation of this design is that you need an extremely high speed
> : clock to reach the upper limit of human hearing with reasonable dynamic
> : range. For example, 16 bits require 65536 clock pulses per sample X
> : 40,000 sample per second = 2,560,000,000 Hz or 2.5 GHz clock speed. But
> : at telephone quality, 12 bits, 4,096 x 8,000 = 32,000,000 Hz or 32 MHz.
> : This is within the range of an FPGA.
>
> Check out how a modern 1 bit D/A convert works. (ie. www.crystal.com)
> It gets away with a much lower clock signal that above by spreading
> the "on" and "off" periods in a noise shaped way amongst the available
> clock periods.
>
> Graeme Gill.

While it is true that they use a much lower clock rate, I believe it is
typical to work at 128 x the sample rate, they are using a large amount of
analog circuitry. I am more familiar with the delta-sigma ADCs. They have a
comparator and an integrator as well as the low pass filter. With a purely
digital approach, I don't see a way to do the same functions.

Rick Collins




Article: 9513
Subject: Re: Looking for space qualified FPGAs/ASICs
From: "rk" <stellare@erols.com.NOSPAM>
Date: 20 Mar 1998 04:10:01 GMT
Links: << >>  << T >>  << A >>
stephen:
: We are looking to encode a complicated algorithm onto either an FPGA or
: ASIC for space applications.
: 
: We are interested to know of any space qualified:
: 
: 1.) FPGAs,

rk:
actel products, act 1, 2, 3, some members only, act 3 looks the best of the
lot right now. rh series, rh1020, rh1280.  dx with ram is a no go, latchup.
 xl has poor rad tolerance from reported data.  40mx, 42mx, no data. 
others "in development" but can't buy so obviously not qualified.

xilinx makes hi-rel, not rad-hard.  need shields + seu protection + latchup
detection.  do-able, depending on application.

also, utmc has ut22vp10 "rad-pal", probably smaller than what you want, but
worth mentioning.
 
stephen:
: 2.) Low volume ASIC processes (e.g. laser programmable, shared wafer
etc),

rk:
some data on chipx.  qyh500 series pretty good, esp. @ 3.3 v.  cx2001
series, poor seu, logic transient, latchup.  btw, laser programmable is
prototype; "one-mask" would be for space-flight.

stephen: 
: 3.) Conventional ASIC processes.

rk:
lots in no particular order.  northrop-grumman, honeywell, harris,
gec/plessey [sold yet?], lockheed-martin, allied-signal, some others.  utmc
went fabless, has announced "commercial rad-hard" with ami.  lsi logic is
out of the business, iirc.


: 
: Thanks for you help in this matter.
: 
: -- 
: Stephen King
: CRL
: sking@crl.co.uk
: 
Article: 9514
Subject: Front page help please // what idems to up load???
From: !!!n5mpa@mci2000.com!!! (Michelle)
Date: Fri, 20 Mar 1998 04:21:22 GMT
Links: << >>  << T >>  << A >>
If you have a web site that doen't support front page extentions, what
files do you have to up load to get the hover buttons to work
properly?  Please help!  Michelle
Article: 9515
Subject: Re: Looking for space qualified FPGAs/ASICs
From: Alasdair MacLean <alasdair.maclean@gecm.com>
Date: Fri, 20 Mar 1998 08:44:55 +0000
Links: << >>  << T >>  << A >>
Stephen King wrote:
> 
> We are looking to encode a complicated algorithm onto either an FPGA or
> ASIC for space applications.
> 
> We are interested to know of any space qualified:
> 
> 1.) FPGAs,
> 

Actel do rad-hard versions of the 1280 and the 1020. The RH1280 comes in
at about $10000 per part, with a min. order of 10. At the moment, I
think they are the only real players. There are other options if you
don't need real rad-hard parts though.

> 2.) Low volume ASIC processes (e.g. laser programmable, shared wafer etc),
> 

Sorry, don't know. NASA have pages and pages of stuff on the subject on
their web pages though.

> 3.) Conventional ASIC processes.
> 

For European Space Agency approved ASIC fabs see
<http://www.estec.esa.nl/xrmwww/asic/asicpr.wsm.htm>

> Thanks for you help in this matter.
> 
> --
> Stephen King
> CRL
> sking@crl.co.uk

Good luck,
Alasdair.

-- 
Alasdair Maclean, Senior Development Engineer,
GEC Marconi Electro-Optics Ltd.,
Building 1A, Room 1-11,
4 Ferry Road, Silverknowes,
Edinburgh, Scotland EH4 4AD
Tel: +44 (0)131 343 5711, Fax: +44 (0)131 343 5050
Email: <mailto:alasdair.maclean@gecm.com>
Article: 9516
Subject: Synthesizable 8B/10B Encoder/Decoder wanted
From: Patrick Mueller <Patrick.Mueller@Schweiz.org>
Date: Fri, 20 Mar 1998 11:13:12 +0100
Links: << >>  << T >>  << A >>
I am searching for a synthesizable 8B/10B Encoder/Decoder for a
FibreChannel Project.
Has anybody VHDL or AHDL code for that?

Thanks

Patrick Mueller

email: no_spam_pbmuelle@stud.ee.ethz.ch ( remove no_spam_ )
Article: 9517
Subject: Actel system available
From: "Douglas W. Olsen" <dwolsen@ra.rockwell.com>
Date: Fri, 20 Mar 1998 09:17:07 -0500
Links: << >>  << T >>  << A >>
FOR SALE    Actel Programming System
		Barely used

        $2500 for all this 
                   (>$7000 new)
Designer Series 3.1 and 3.1.1 Software
  (Product code DAT-PC)
   All disks and documentation intact

Activator 2S Hardware Programmer
   with ACT12-144PQFP adapter
   Used three times

ALS-218 Action Probe (debugger)
   never used

        $2500

Contact:
-----------------------------------------------------------
Douglas W. Olsen     | voice:   770.622.6286               |
Rockwell Automation  | FAX:     770.623.9163               |
2150 Boggs Road      | email:   dwolsen@ra.rockwell.com    |
Duluth, GA 30096     |
Article: 9518
Subject: Canadian Career Opportunity
From: Nancy Kotecki <NancyK@priorresource.com>
Date: Fri, 20 Mar 1998 09:28:29 -0500
Links: << >>  << T >>  << A >>
We are a hi-tech recruiting firm located in "Canada's Technology
Triangle" (Kitchener-Waterloo, Guelph, Cambridge).  This is an exciting,
vibrant area with tremendous new technologies being developed by
hundreds of hi-tech companies.  We have an immediate (and URGENT) need
for a Senior Design Engineer to deliver leading edge design solutions
and enhancements for projection products.  Design disciplines include
high speed digital circuits to process video and graphic images, fast
A/D conversion, phase lock loop, FPGA/PLD designs to support the above,
and an understanding of video analogue circuits.  An electrical
engineering degree and three to five years design experience would be
appropriate.  This opportunity will allow an individual to succeed on a
highly skilled team developing exciting new products.

Please reply to NancyK@PriorResource.com
For more opportunities and information about this wonderful area, check
our web site at www.PriorResource.com

Article: 9519
Subject: Linux Xchecker Downloads?
From: kz@uni.uiuc.edu (Casey Smith)
Date: 20 Mar 1998 14:39:43 GMT
Links: << >>  << T >>  << A >>
	Does anyone out there know where I can get software (bin or ready
 to compile) for Linux to download bitfiles to Xilinx FPGA's via Xchecker?

					Thanks Much,
					kz
					cjsmith@uiuc.edu
Article: 9520
Subject: Re: Ideas for an FPGA Project?
From: James Horn <jimhorn@svn.net>
Date: 20 Mar 1998 18:15:49 GMT
Links: << >>  << T >>  << A >>
> While it is true that they use a much lower clock rate, I believe it is
> typical to work at 128 x the sample rate, they are using a large amount of
> analog circuitry. I am more familiar with the delta-sigma ADCs. They have a
> comparator and an integrator as well as the low pass filter. With a purely
> digital approach, I don't see a way to do the same functions.

> Rick Collins

Hi Rick -

It's not obvious, but check the actual operation.  The high-speed 1 bit
DACs are *entirely digital* except for the simple filter to convert the 11
MHz On/Off bitstream to 16 bit audio analog.  That filter can easily be a
simple RC filter - it only needs to eliminate noise above a MHz or so.
Yes, that *is* hard to believe.

If you play with clever algorithms (the noise-spreading ideas mentioned),
you can get 2 bits of DAC simplification for every bit of time resolution
(i.e. doubling of bit rate).  So by adding 8 bits of time resolution -
increasing the clock rate by 256 to 1 - you can get 16 bits of DAC
performance with a 1 bit output.  It *does* require a lot of fast
computation.  But nowadays that's nearly free and very easy.  And the
results don't need .001% precision resistors or other parts to be
monotonic and linear.

It still strikes me as one of the cleverer consumer electronics bits of
DSP I've run across.

Jim Horn


Article: 9521
Subject: Dual port
From: jamil.khatib@pemail.net (J. Khatib)
Date: Fri, 20 Mar 1998 19:22:15 GMT
Links: << >>  << T >>  << A >>
What is the  dual   port memory?

thanks in advance
Article: 9522
Subject: Re: Looking for space qualified FPGAs/ASICs
From: "rk" <stellare@erols.com.NOSPAM>
Date: 20 Mar 1998 20:33:08 GMT
Links: << >>  << T >>  << A >>
stephen:

: Actel do rad-hard versions of the 1280 and the 1020. The RH1280 comes in
: at about $10000 per part, with a min. order of 10. At the moment, I
: think they are the only real players. There are other options if you
: don't need real rad-hard parts though.

rk:
"rad-hard" is a term to be used, well, carefully.  it needs to be broken
down into total dose, single event upset, single event latchup, single
event transient, and "other destructive effects" such as antifuse or gate
rupture.  to the best of my knowledge, there is no full rad-hard fpga in
existence, although there are some nice models which do extremely well at
some parameters and moderately well at others.

stephen:
: > 2.) Low volume ASIC processes (e.g. laser programmable, shared wafer
etc),
: > 
: 
: Sorry, don't know. NASA have pages and pages of stuff on the subject on
: their web pages though.

rk:
try:	http://rk.gsfc.nasa.gov
	http://flick.gsfc.nasa.gov/radhome

--------------------------------------------------------------
rk

"there's nothing like real data to screw up a great theory" 
- me (modified from original, slightly more colorful version)
--------------------------------------------------------------
Article: 9523
Subject: To: Paul Young of Caterpillar
From: Richard Schwarz <aps@associatedpro.com>
Date: Fri, 20 Mar 1998 20:02:09 -0500
Links: << >>  << T >>  << A >>
This is a multi-part message in MIME format.
--------------18F5C47642229781E861755F
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Paul Young of Caterpillar,

Paul we have seen your numerous posts to COMP.ARCH.FPGA. We understand
that you have had some concerns about a missed shipping date around the
Christmas time frame.

We are more than willing to try and resolve this, and in fact have
offered to
refund your shipping costs, out of our pockets. We did pursue the matter
with UPS, and they didn't have any idea what we were talking about. You
are free to pursue the matter with UPS also if you wish, but why do so,
when we have already offered to refund your shipments even if we don't
get a refund from UPS.

I believe your story about the UPS operator , and I believe that there
was a
mix up on the date you wanted the board shipped. I will not publicly
hammer UPS
(after all it was Christmas time). You requested a delayed shipment and
we
tried to accommodate you, but apparently there was a misunderstanding
and we
shipped the board on the day you wanted it to arrive. We further tried
to
accommodate you by doing a partial shipment because the manual was out
of
stock. We never charged you for the second shipment of the manual.

Now Paul,  please don't continue to take pot shots at us publicly in
this way.
You made your point that you were unhappy with UPS and with us. We are
still
willing to resolve it in any reasonable way possible. Let us do this,
without
having the public discussions on the internet, where we are forced to
defend
ourselves publicly. This does not reflect well on either of us.

For future reference we CAN NOT and WILL NOT and DID NOT guarantee any
DELAYED
target shipment dates. We DID and WILL try to accommodate any and all
customer requests to the best of our ability, and WILL continue to do
so.We WILL
overnight materials when requested and when in stock. This is standard
practice. We do understand your expectations were not met, and we will
refund
ALL of your shipping costs, in order to satisfy you. Beyond this, I
don't know
what else we can do.

Please email me directly at richard@associatedpro.com for further

Respectfully,

Richard D. Schwarz
President, APS


--
__/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/

    Richard Schwarz, President
    Associated Professional Systems Inc. (APS)
    email: richard@associatedpro.com
    web site: http://www.associatedpro.com
    Phone: 410-569-5897
    Fax:   410-661-2760

__/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/




  Richard Schwarz
  President
  Associated Professional Systems
                          <aps@associatedpro.com>
  3003 Latrobe Court
  Abingdon
  MD
  21009
  USA
                          Work: 410.569.5897
                          Fax: 410.661.2760
                          Home: 410.515.3883
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  Additional Information:
  Last Name
           Schwarz
  First Name
           Richard
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           2.1





--
__/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/

    Richard Schwarz, President
    Associated Professional Systems Inc. (APS)
    email: richard@associatedpro.com
    web site: http://www.associatedpro.com
    Phone: 410-569-5897
    Fax:   410-661-2760

__/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/ __/


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--------------18F5C47642229781E861755F--

Article: 9524
Subject: Re: Ideas for an FPGA Project?
From: Rick Collins <redsp@writeme.com>
Date: Fri, 20 Mar 1998 20:47:03 -0500
Links: << >>  << T >>  << A >>
James Horn wrote:

> > While it is true that they use a much lower clock rate, I believe it is
> > typical to work at 128 x the sample rate, they are using a large amount of
> > analog circuitry. I am more familiar with the delta-sigma ADCs. They have a
> > comparator and an integrator as well as the low pass filter. With a purely
> > digital approach, I don't see a way to do the same functions.
>
> > Rick Collins
>
> Hi Rick -
>
> It's not obvious, but check the actual operation.  The high-speed 1 bit
> DACs are *entirely digital* except for the simple filter to convert the 11
> MHz On/Off bitstream to 16 bit audio analog.  That filter can easily be a
> simple RC filter - it only needs to eliminate noise above a MHz or so.
> Yes, that *is* hard to believe.
>
> If you play with clever algorithms (the noise-spreading ideas mentioned),
> you can get 2 bits of DAC simplification for every bit of time resolution
> (i.e. doubling of bit rate).  So by adding 8 bits of time resolution -
> increasing the clock rate by 256 to 1 - you can get 16 bits of DAC
> performance with a 1 bit output.  It *does* require a lot of fast
> computation.  But nowadays that's nearly free and very easy.  And the
> results don't need .001% precision resistors or other parts to be
> monotonic and linear.
>
> It still strikes me as one of the cleverer consumer electronics bits of
> DSP I've run across.
>
> Jim Horn

I am having trouble finding a good explaination of the delta-sigma DAC. But what
I have read about the sigma-delta ADC is that a fair amount of analog circuitry
is required on the chip. This is in the modulator and consists of a Summer (op
amp) Integrator and Comparator (one bit ADC).   I would assume that similar
components must make up the delta-sigma DAC.

BTW, I have seen the term used both ways; delta-sigma and sigma-delta. Is one for
the ADC and the other for the DAC, or are they interchangable?


Rick Collins


redsp@writeme.com





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