Where to get high speed ADC's and DACs

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.

--

John Devereux

Thank you for the info.

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

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.

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.

--
Regards, Joerg 

http://www.analogconsultants.com/

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?

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

--

John Devereux

You have it backwards. The one-bit ADCs used in GPS receivers are followed by a system that has lots and lots of coding gain. The _signal_ has to be pulled out of the noise correctly and continually, but the ADC value includes lots of noise.

--

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

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.

--

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

I was making 8-bit DAC's in the mid-60's, and no trimming required. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

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

In the early 80's ITT made the best ones, and cheap. I used them in my master's project.

You've got mail.

--
Regards, Joerg 

http://www.analogconsultants.com/

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

-Lasse

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

1. 2**20 ~= 10**6.

Therefore, 1 LSB ~= 5 uV.

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

1. 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).

2. 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.

1. IOW, good luck.

That's just engineering rules of thumb.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net

Am 02.09.2013 19:17, schrieb RobertMacy:

Yes, we used it also: <

>

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.

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 <

>

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

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.

(Context restored)

So apart from posturing, what do you actually disagree with, and why?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net

Don't take umbrage. I don't think I disagree. I'm sure everything you said was correct, and as you said, they are rules of thumb for engineering. It's just that nothing there was useful for me. Well, at first glance seemed like almost nothing. I couldn't see how to apply all you said to what I'm doing.

In retrospect, not nothing, because you made me THINK. Your comment, 'good luck with that' challenged my thinking. Perhaps, I was wrong in what I was doing. So I went back to my basic system and had to recreate all my equations from ground zero back up to try operating at 10-100MS/s rates. Why ground zero? I don't even trust my own equations. I question EVERYTHING. So four hours of intensive effort later, I verified a lot and feel better, thanks. Plus, you triggered a topological approach using 'available' parts that had NEVER occurred to me until just now. And, all those recreated equations allowed me to verify [not rigorously, but at least a bit empirically] that the approach would be possible. Even better, for my requirements, I might even be able to get more than 24 bits at

100MS/s.

Gone brain dead here, have I sent any images of results using the present system to you? If not, send me an email address, and I'll send a couple.

How are you measuring that 22.5 bits?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

As with most of the measurements, made them, continually have their values verified indirectly while using the system, so don't revisit.

(Context restored again)

The address in my sig works. You haven't given any details, but very simple and compelling arguments of the above sort tell me that you aren't getting anywhere near 22 bits at 100 MHz, unless you're using all low-TC SQUID-based circuitry.

If I'm wrong about that, and you really have found a way to do it for real, you're going to be extremely famous in very short order.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net