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Where to get high speed ADC's and DACs

R

RobertMacy

Jan 1, 1970
0
Where do I get 24 bit high speed ADC and DAC systems out to 10MHz?

Or, turn around how much digitization can I get out to 100MHz today? 20
bits?
 
R

RobertMacy

Jan 1, 1970
0
This is about right:

http://www.linear.com/designtools/hsadcs.php


We use their 250 MHz, 12-bit LVDS ADC and it's pretty good.

https://dl.dropboxusercontent.com/u/53724080/PCBs/ESM_rev_B.jpg

A 20 or 24-bit ADC, at 100 MHz, probably isn't useful. Wideband noise
would
trash a lot of LSBs.


John,

You have no idea how much I respect Linear and their products. but I was
talking about 20+bits not the insignificant 12 bit range.

[I recently did 18 bits at 500MHz - Jim Williams would have been proud,
NEVER AGAIN!!!

From simulations, I need 20+ bits, else quantization noise eats me alive!
 
R

RobertMacy

Jan 1, 1970
0
Sure thing. Just use two 10-bit ADCs and put a 60 dB pad in front of
one of them. ;)

Cheers

Phil Hobbs

PHIL! Not funny! well maybe, a bit, still LOL
 
R

RobertMacy

Jan 1, 1970
0
Way back in the design days for the L1011, I suggested a seat-audio
system made up of two 8-bit DAC's, one basically volume riding, and
the other the "detail".

Demonstrated it. Sounded great. Rejected in spite of how inexpensive
it was. They went with a much more expensive 12-bit DAC.

...Jim Thompson

Don't get me started on 'closed mindedness'!

Back around 1966, I designed the hardware computer interface for L1011.
Going from that environment [aerospace and autopilots] to HP' RF/Microwave
Lab, noted for their conservative designs, was like being thrust into the
sloppiest garage designers I'd ever seen! Imagine what it was like to go
from that into coin-opeated electronic games!
 
R

RobertMacy

Jan 1, 1970
0
You can get true 24 bit performance in a bandwidth of somewhat like 50Hz
(current state of art).
For 100 MHz bandwidth, you just have to parrallel 2000000 frequency
split channels.


VLV

Vladimir,

I know your answer was 'tongue in cheek' but you actually have made me
think about directions/concepts that had NOT occurred to me before. Thanks.

Interesting about that bandwidth. TI makes a 24 bit seismic ADC [ADS1282?]
that just about has that bandwidth. Give me an email address and I'll send
you an example of using a PCB Layout Tool I created for checking PCB Plane
noise around uP, etc and ADC. I used the tool to check the efficacy of a
'first pass' PCB layout design using that chip. The tool showed were
better than 1/4 LSB noise.
 
John,

You have no idea how much I respect Linear and their products. but I was
talking about 20+bits not the insignificant 12 bit range.

At least a few years ago getting 120 dB SNR with 20 kHz audio
bandwidth was quite normal (20 bits at 50 kHz) or in scales getting 24
bits with 1-2 samples/second.
[I recently did 18 bits at 500MHz - Jim Williams would have been proud,
NEVER AGAIN!!!

From simulations, I need 20+ bits, else quantization noise eats me alive!

Is adding dithering noise out of the question ?
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
At least a few years ago getting 120 dB SNR with 20 kHz audio
bandwidth was quite normal (20 bits at 50 kHz) or in scales getting 24
bits with 1-2 samples/second.
[I recently did 18 bits at 500MHz - Jim Williams would have been proud,
NEVER AGAIN!!!

From simulations, I need 20+ bits, else quantization noise eats me alive!
Is adding dithering noise out of the question ?



Look into what GPS receivers use.



They are the lowest level signals we discriminate currently. They

reside just above the noise floor. At -127.5 dBm.



But that is a receiver signal value, not an ADC SNL function.

Still, one might find some pointers by examining what those folks do.

GPS only use a few bits of adc if not only one bit ...



-Lasse
 
On Sun, 01 Sep 2013 09:44:40 -0700, John Larkin

Where do I get 24 bit high speed ADC and DAC systems out to 10MHz?

Or, turn around how much digitization can I get out to 100MHz today? 20
bits?

This is about right:

http://www.linear.com/designtools/hsadcs.php


We use their 250 MHz, 12-bit LVDS ADC and it's pretty good.

https://dl.dropboxusercontent.com/u/53724080/PCBs/ESM_rev_B.jpg

A 20 or 24-bit ADC, at 100 MHz, probably isn't useful. Wideband noise
would
trash a lot of LSBs.




John,

You have no idea how much I respect Linear and their products. but I was
talking about 20+bits not the insignificant 12 bit range.

At least a few years ago getting 120 dB SNR with 20 kHz audio
bandwidth was quite normal (20 bits at 50 kHz) or in scales getting 24
bits with 1-2 samples/second.
[I recently did 18 bits at 500MHz - Jim Williams would have been proud,
NEVER AGAIN!!!

From simulations, I need 20+ bits, else quantization noise eats me alive!

Is adding dithering noise out of the question ?

Look into what GPS receivers use.

They are the lowest level signals we discriminate currently. They
reside just above the noise floor. At -127.5 dBm.

I guess that I am responding to a troll, but anyway.

With a primitive antenna, it will see partly the "warm" earth at 300 K
as well as the cold sky 3 K (cosmic background radiation). Assuming
worst case 300 K antenna temperature, this corresponds to -174 dBm/Hz.
The GPS data telegrams (such as the almanak) are transimtted at 50
bit/s data rate, thus someting like -157 dBm is required.

The PRN 1000 Hz signal repetition sequence would suggest 1 kHz
bandwidth and -144 dBm signal levels.

Considering the 1.023 MHz chip rate and similar bandwidths, the needed
signal is about -117 dBm.

I have no real understanding, what -127.5 dBm might mean ?

For an unknown startup location and no bit sync, that would be a good
figure. For synchronized data extraction at -127 dBm that would be
quite bad.
 
R

RobertMacy

Jan 1, 1970
0
Well, if we generously assume that an ADC that fast could have a 5V
input range, 1 LSB at 20 bits is 5 uV, and the quantization noise is
1/sqrt(12) times that, or 1.4 uV. In a 100 MHz bandwidth, that's
140 pV/sqrt(Hz). In real life, the input structure would have to be
several times faster than that in order to settle to that accuracy in
the time available, putting the maximum input noise down in the
50 pV/sqrt(Hz) range, not counting the effects of input capacitance.

Good luck with that.

Cheers

Phil Hobbs

Irritated yelling mode...You have just demonstrated once again WHY I
re-derive EVERYTHING! I NEVER trust 'cookbook' equations, especially after
getting severely burnt by an article in EDN showing 'cookbook' values for
a simple 'what's its name? filter [the simple 5-pole low pass type using
two 2N3904's in series]. Whereupon, I was forced to rederive ALL the
values for both Butterworth AND Tschebyshev(sp?) *and* using an HP
calculator with reverse polish input (spit, spit, curse begone!) I
'optimized' a response to obtain values and voila! worked. But that little
effort caught me on a late Friday [deadline Monday morning] to make a
filter that worked! All weekend!

I HATE PACKAGED FORMULAS!!! I have NO idea what these numbers you gave me
should mean to me.

Now back to quiet mode...Thank you for providing 'numbers', although I
have NO idea what they mean, nor how they relate to what I'm doing. I just
checked and found that *if* I use 16 bit 10MHz ADC's in my system, the
system will be next to useless. *IF* I can get 22 bits, it will work
almost as well as the previous system. Probably live with 20 bits, but the
performance is going to suffer.

Digitization noise dominates in my system, NOT the noise density function.
Front end can be lousy at 2nV/rtHz, prefer 1nV/rtHz [50 ohm system], BW is
cutoff at 20MHz, digitize -1V to +1V to 20 bits at 10MS/s the system will
just barely make it. If could digitize to 22 bits, the system will work
acceptibly!

So back to...

Who makes a 20+ bit ADC with 10MS/s capability?

Who makes a 22-24 bit DAC that can operate this fast?
 
J

John Devereux

Jan 1, 1970
0
RobertMacy said:
Well, if we generously assume that an ADC that fast could have a 5V
input range, 1 LSB at 20 bits is 5 uV, and the quantization noise is
1/sqrt(12) times that, or 1.4 uV. In a 100 MHz bandwidth, that's
140 pV/sqrt(Hz). In real life, the input structure would have to be
several times faster than that in order to settle to that accuracy
in the time available, putting the maximum input noise down in the
50 pV/sqrt(Hz) range, not counting the effects of input capacitance.

Good luck with that.

Cheers

Phil Hobbs

Irritated yelling mode...You have just demonstrated once again WHY I
re-derive EVERYTHING! I NEVER trust 'cookbook' equations, especially
after getting severely burnt by an article in EDN showing 'cookbook'
values for a simple 'what's its name? filter [the simple 5-pole low
pass type using two 2N3904's in series]. Whereupon, I was forced to
rederive ALL the values for both Butterworth AND Tschebyshev(sp?)
*and* using an HP calculator with reverse polish input (spit, spit,
curse begone!) I 'optimized' a response to obtain values and voila!
worked. But that little effort caught me on a late Friday [deadline
Monday morning] to make a filter that worked! All weekend!

I HATE PACKAGED FORMULAS!!! I have NO idea what these numbers you gave
me should mean to me.

Now back to quiet mode...Thank you for providing 'numbers', although I
have NO idea what they mean, nor how they relate to what I'm doing. I
just checked and found that *if* I use 16 bit 10MHz ADC's in my
system, the system will be next to useless. *IF* I can get 22 bits, it
will work almost as well as the previous system. Probably live with 20
bits, but the performance is going to suffer.

Digitization noise dominates in my system, NOT the noise density
function. Front end can be lousy at 2nV/rtHz, prefer 1nV/rtHz [50 ohm
system], BW is cutoff at 20MHz, digitize -1V to +1V to 20 bits at
10MS/s the system will just barely make it. If could digitize to 22
bits, the system will work acceptibly!

So back to...

Who makes a 20+ bit ADC with 10MS/s capability?

Nobody.

Linear have just released a 20 bit 1MSPS, this is state of the art
AFAIK.
Who makes a 22-24 bit DAC that can operate this fast?

Don't think they make 22+ bit DACs at all, although it would be possible
in principle.
 
R

RobertMacy

Jan 1, 1970
0
Nobody.

Linear have just released a 20 bit 1MSPS, this is state of the art
AFAIK.


Don't think they make 22+ bit DACs at all, although it would be possible
in principle.

Thank you for the info.
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
Well, if we generously assume that an ADC that fast could have a 5V
input range, 1 LSB at 20 bits is 5 uV, and the quantization noise is
1/sqrt(12) times that, or 1.4 uV. In a 100 MHz bandwidth, that's
140 pV/sqrt(Hz). In real life, the input structure would have to be
several times faster than that in order to settle to that accuracy in
the time available, putting the maximum input noise down in the
50 pV/sqrt(Hz) range, not counting the effects of input capacitance.

Good luck with that.



Phil Hobbs



Irritated yelling mode...You have just demonstrated once again WHY I

re-derive EVERYTHING! I NEVER trust 'cookbook' equations, especially after

getting severely burnt by an article in EDN showing 'cookbook' values for

a simple 'what's its name? filter [the simple 5-pole low pass type using

two 2N3904's in series]. Whereupon, I was forced to rederive ALL the

values for both Butterworth AND Tschebyshev(sp?) *and* using an HP

calculator with reverse polish input (spit, spit, curse begone!) I

'optimized' a response to obtain values and voila! worked. But that little

effort caught me on a late Friday [deadline Monday morning] to make a

filter that worked! All weekend!



I HATE PACKAGED FORMULAS!!! I have NO idea what these numbers you gave me

should mean to me.



Now back to quiet mode...Thank you for providing 'numbers', although I

have NO idea what they mean, nor how they relate to what I'm doing. I just

checked and found that *if* I use 16 bit 10MHz ADC's in my system, the

system will be next to useless. *IF* I can get 22 bits, it will work

almost as well as the previous system. Probably live with 20 bits, but the

performance is going to suffer.



Digitization noise dominates in my system, NOT the noise density function.

Front end can be lousy at 2nV/rtHz, prefer 1nV/rtHz [50 ohm system], BW is

cutoff at 20MHz, digitize -1V to +1V to 20 bits at 10MS/s the system will

just barely make it. If could digitize to 22 bits, the system will work

acceptibly!



So back to...



Who makes a 20+ bit ADC with 10MS/s capability?

I probaly missing something but what would be the point of
make a 24 bit adc if the 8 lsb will be noise at that
bandwidth in a 50R system?

-Lasse
 
J

Joerg

Jan 1, 1970
0
Well, there's the solution :)

Thank you for the info.


Considering the specs you set out with this seems to be a project of the
budget category "the sky is the limit". So you could take 10 of these
LTC converters, add 10 track&hold circuits if needed, and pipe the
resulting barrage of data to wherever it needs to be crunched.

No kidding, that's how we did high-end ultrasound machines in the days
when 12-bit converters were too slow for the job. If you decide to go
that route and need ways to auto-align them for offset, gain and
aperture jitter let me know because I've BTDT. The ones I've been
involved in had between four and 32 converters ganged. My DSO works the
same way when operating single or dual channel, it has four converters
that are ganged if you don't use all four channels.
 
R

RobertMacy

Jan 1, 1970
0
Considering the specs you set out with this seems to be a project of the
budget category "the sky is the limit". So you could take 10 of these
LTC converters, add 10 track&hold circuits if needed, and pipe the
resulting barrage of data to wherever it needs to be crunched.

No kidding, that's how we did high-end ultrasound machines in the days
when 12-bit converters were too slow for the job. If you decide to go
that route and need ways to auto-align them for offset, gain and
aperture jitter let me know because I've BTDT. The ones I've been
involved in had between four and 32 converters ganged. My DSO works the
same way when operating single or dual channel, it has four converters
that are ganged if you don't use all four channels.

sadly not 'sky limit' budget.

I remember those ultrasonic days. Late 70's? I remember the excitement
from getting an 8 bit ADC, much better than the previous 6 bit one, didn't
TRW make it? came in a ?? 64 pin ceramic DIP package, the size of a small
chocolate bar. and ran HOT!


10 S/H's multiplexed into 10 ADC's could work, interesting. although do
need at least two channels.

More detail offline? Or can you share here?
 
J

John Devereux

Jan 1, 1970
0
Joerg said:
Well, there's the solution :)




Considering the specs you set out with this seems to be a project of the
budget category "the sky is the limit". So you could take 10 of these
LTC converters, add 10 track&hold circuits if needed, and pipe the
resulting barrage of data to wherever it needs to be crunched.

Yes, Vlads Solution, downscaled into the realms of possibility.
 
J

Joerg

Jan 1, 1970
0
RobertMacy said:
sadly not 'sky limit' budget.

That would mean the proverbial rock and hard spot. "We want creme brulee
but we can only pay a buck fifty".

I remember those ultrasonic days. Late 70's? I remember the excitement
from getting an 8 bit ADC, much better than the previous 6 bit one,
didn't TRW make it? came in a ?? 64 pin ceramic DIP package, the size of
a small chocolate bar. and ran HOT!

In the early 80's ITT made the best ones, and cheap. I used them in my
master's project.
10 S/H's multiplexed into 10 ADC's could work, interesting. although do
need at least two channels.

More detail offline? Or can you share here?


You've got mail.
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
On Sun, 01 Sep 2013 09:44:40 -0700, John Larkin

On Sun, 01 Sep 2013 09:33:15 -0700, RobertMacy
<[email protected]>
wrote:

Where do I get 24 bit high speed ADC and DAC systems out to 10MHz?

Or, turn around how much digitization can I get out to 100MHz today?
20 bits?

This is about right:

http://www.linear.com/designtools/hsadcs.php


We use their 250 MHz, 12-bit LVDS ADC and it's pretty good.

https://dl.dropboxusercontent.com/u/53724080/PCBs/ESM_rev_B.jpg

A 20 or 24-bit ADC, at 100 MHz, probably isn't useful. Wideband noise
would trash a lot of LSBs.




John,

You have no idea how much I respect Linear and their products. but I was
talking about 20+bits not the insignificant 12 bit range.
They have 16 bits at 185 Ms/s.
[I recently did 18 bits at 500MHz - Jim Williams would have been proud,
NEVER AGAIN!!!

From simulations, I need 20+ bits, else quantization noise eats me
alive!
At 500 MHz bandwidth (reasonable s/h bw for a 500 Ms/s ADC) a 50 ohm
resistor makes 20 uV RMS Johnson noise, and I doubt that any actual
front-end amp will be anywhere close to that, probably several times
worse. Seems to me that you'll have many LSBs of noise, which may be OK
if downstream processing is essentially narrowband, like some RF stuff.



John's nailed it.



The determining factor is the noise in the front end of the ADC, and

that's going to be much higher than Johnson noise for a monolithic device.



There may be some ultra-boutique hybrid parts out there that can extend

this, but they'll still be limited by the noise in the comparator and the

need for a high bit-count DAC.



If you really need a 144dB full scale to LSB ratio before the noise

starts interfering with your measurement, then at 10MHz you're probably

screwed. If there is some device that can do this, it's almost certainly

not a chip.



But -- what do you really need? Are you really using the full bandwidth

of this thing, or are you extracting some narrower-bandwidth signal out

of it? Averaging the output of an ADC can do wonders for the precision

of the measurement.

just like a deltasigma adc, but you just trade precision for bandwidth


-Lasse
 
G

Gerhard Hoffmann

Jan 1, 1970
0
Am 02.09.2013 19:17, schrieb RobertMacy:
I remember those ultrasonic days. Late 70's? I remember the excitement
from getting an 8 bit ADC, much better than the previous 6 bit one,
didn't TRW make it? came in a ?? 64 pin ceramic DIP package, the size of
a small chocolate bar. and ran HOT!

Yes, we used it also:
< http://www.hoffmann-hochfrequenz.de/project_gallery/project_gallery.html >

Third picture from the top, as blurred background for its successor.
Lower right, the big white letters said "TRW". We also got a nekkid one
in a cube of Plexiglas. One could see the reference ladder without
microscope.

That was for testing the inner enclosure of nuclear reactors with
ultrasonics.
10 S/H's multiplexed into 10 ADC's could work, interesting. although do
need at least two channels.

You cannot buy interesting S/Hs nowadays, unless you accept an
ADC on the same chip. So you probably end up at the LTC2209 or its
competitors from AD and TI.

When TI had no 100MHz 16Bit ADC to offer, they published an app note
on averaging some 14 bit ADCs to get better dynamic range. Quite
interesting. I'd really like to try that. It is probably easier
than a time staggered setup since you can shift the sampling window
to a moment when the digital part is quiet.
Also there is much less danger of messing up the sampling clock.
(phase noise, spurs..)

Averaging over a large number of parts works nicely as in
< http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf >

Yes, brute force! Nothing to tune or even select.
And crossing the A to D boundary makes no systematic difference.

BTW something like that could be useful to check your supplies
and reference voltages.

regards, Gerhard
 
R

RobertMacy

Jan 1, 1970
0
Sorry? Surely anybody designing high performance A/D subsystems knows
that 2**10 ~= 1000, that the RMS quantization noise of an ideal
digitizer is 1/sqrt(12) of the LSB, and that the noise is more or less
white? You can derive it yourself in about three lines.

All I'm saying is:

1. 1 LSB = FSR/2**N

2. 2**20 ~= 10**6.

Therefore, 1 LSB ~= 5 uV.

3. RMS quantization noise is 1/sqrt(12)* 1 LSB ~= 5 uV/3.46 ~= 1.4 uV,
spread out evenly over the Nyquist interval.

4. The Nyquist bandwidth is 50 MHz (not 100), so given that the noise is
white, the quantization noise PSD is 1.4 uV/sqrt(50 MHz) ~=200
pV/sqrt(Hz).

5. To get that many bits to stay reasonably still, your RMS input noise
has to be well below that. Even slow delta-sigmas are hard pressed to
reach a genuine 20 bits, and most of them actually crap out around 18 or
19, AFAICT.

6. IOW, good luck.

That's just engineering rules of thumb.

Cheers

Phil Hobbs


Sorry? LOL! I actually read that out loud for effect.

In the present 24 bit Data Acquisition system I get something like a
measured 22.5 bits, meaning not quite 23, but better than 22. And, I
couldn't believe I actually ran up to 91% of the Nyquist rate! but I
backed it off down to 89% so didn't see ANY limiting effects.

I tell youu I'm REALLY impressed with this board! buried inside a PC
WITHOUT shielding! I have more trouble from picking up noise from the SMPS
buried inside the LCD scope sitting next to the breadboard. And don't get
me started on having an old CRT monitor turned on in the lab, ...across
the room.
 
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