Where to get high speed ADC's and DACs

This is about right:

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

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

--

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

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

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

It's cheaper to concatenate the output of a 10-bit ADC with a 10-bit random sequence generator.

--

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

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!

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

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

--
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

But not nearly as sexy.

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

--
| 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  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

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

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!

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.

I remember vividly the experience of pitching Footprints(*) to a major manufacturer of commercial control systems. (You'd recognize the name instantly.)

At the time, they were buying 256-pixel IR sensors for $4000 apiece, which weren't as good as my $100 ones. We pitched it like this:

"You're paying $4k * 1000 units = $4M per year now. Our technology will cost you $100 per unit plus a $50 royalty, i.e. $150k per year."

What we expected them to say: "Wow, we can save $3.85M per year! Let's buy a house in Aruba!

What they actually said: "That's a FIFTY PERCENT ROYALTY! Are you out of your MIND?"

A classical example of inside-the-box thinking, as I later realized. I'd led a very sheltered life up to then, and had never really encountered it before.

Cheers

Phil Hobbs

(*) Footprints was a distributed system of $10-ish IR imagers with $50-ish back ends, about $100 installed. See

.

--
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

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.

Is adding dithering noise out of the question ?

On Sun, 01 Sep 2013 22:21:15 +0300, snipped-for-privacy@downunder.com Gave us:

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

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.

They have 16 bits at 185 Ms/s.

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 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

I made Metricom an offer to save them about $20 per electrical meter, for a $1 royalty. They said "no, but how would you like to be a consultant?"

I'm still here, and they aren't.

I also designed some slick multichannel electric survey meters for Synergistic Control Systems, for a 15% royalty. They sold thousands, and hired a design house to get rid of me, and dumped over a megabuck for nothing useful. They're gone, too.

--

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

analog has 16bits at 250MHz

-Lasse

On Sun, 1 Sep 2013 13:43:25 -0700 (PDT), Lasse Langwadt Christensen Gave us:

One *still* must pull that bit out of the noise... correctly, continually.