Fast adc

[Alex555]

Does anybody know of a 12-16 bit DIP ADC with two channels and a one megahertz sample rate or one channel and a two megahertz sample rate? I also need a parallel interface, or at least be able to get half of its data at a time.

[matseng]

That might be a problem... Something like AD1671 (12 bit, 1.25M sample rate) might work, if you can find one in stock, and if your're willing to pay about $100 for it and you need two of them since thay are only single channel, but thay are in DIP format at least. http://www.analog.com/en/analog-to-digi ... oduct.html

Or go if you can accept soic28 (easy to solder or just put it on a soic->dip breakout) you can have a AD9223ARZ for $15 - 3M sample rate 12 bit.

Both have full 12 bit parallel outputs.

[ian]

I think in this range most "parallel flash ADCs" (good search term I think) are going to be in SOIC, but it is super easy to solder. Ti has a bunch available in different resolutions.

[Alex555]

SOIC is through hole, right? If so I can use that fairly easily.

[SolderSplashLabs]

Nope sorry SOIC is surface mount, still fairly easy to hand solder though

http://en.wikipedia.org/wiki/Small-outl ... ed_circuit

[Alex555]

Where can I find aAD9223ARZ for $15? Everywhere I looked sold it for $30 or more, or had extreme shipping costs. Also, will a wire wrapped board be sufficient and is there anything I need to consider as far as power supply noise, or input filtering?

[matseng]

In singles from a distributor you probably have to shell out a little bit more than $15 - http://www.digikey.com/product-search/e ... =AD9223ARZ is $20. Shipping costs depends on where you're located - I guess that your're not living in the US?

12 bits isn't that much so it will survive a bit of noise at the power rails without losing too much of precision. But still, you will have a system with mixed digital and (rather) high frequency analog signals so proper electronics design is mandatory to keep the digital stuff from destroying your analogue signals - especially if they are low level.

Unless you're sufficiently experienced I strongly suggest that you open a new project thread and tell us what you're going to build and with what parts and see if the DP community can help you out with the design and hints for getting it to work properly in real life and not only on paper.


Ian.... It would be fun to see a world heatmap based on the country of the last ip address each user had for his(hers) last login.

[Alex555]

I am very experienced with digital circuitry, (7400 logic, not microcontrollers, cpld, fpga, etc.) I am in the U.S., but for some reason I thought it was digikey that cost a ton for shipping. I plan on making a portable storage oscilloscope, terminal, logic analyzer, waveform generator, and any other measurement tools/pong I can program into it.

[matseng]

Meh.... My last order from Digikey delivered to an US address was $2.80 for First class mail or $5.10 for Priority Mail. I suppose they might have changed something in the last few months or so, but it seems unlikely....

Ok, just from the top of my head:

Decouple heavy and varied (like 0.1u+2.2u+10u) everywhere. Separate the analogue and digital power powers. Have different ground planes and joined at only one place. Filter the power with LC-networks (ferrite beads+caps). Separate analogue and digital circuits physically on the board. Put lowpass filters at in inputs of the a/d to remove frequencies above the Nyquist frequency. Put guard rings around sensitive analogue nets.

I'm sure there are more things to look out for... :-)

[Alex555]

Is there any way I can do some of that on a wire wrap board? PCBs are to expensive. I can connect all grounds only in one place, put caps everywhere, and I can isolate supplies. I can also surround the board with grounded sheet metal, if that will help, and the adc will be on a board all of its own. I may need help with the inductor/ capacitor values, especially at the input filters.

[matseng]

Wirewrap is actually the ultimate multilayer pcb. The wires can be as short as possible directly from point-to-point so they don't need to snake around the board. You can make faked twisted-pair "transmission lines" by twisting two wires and connect them to signal/ground. By having straight/short wires the inductance is minimized.

It's of course hard to to proper ground plane and high amperage power buses - but the power can be taken care of by soldering a bit heavier wires to the sockets at the bottom of the pcb. The sockets will be harder to reuse after that, but it is a solution when high power is needed at least.

For ultimate short connections of capacitors you can solder them directly either directly onto the leads of the ICs or at the bottom of the pcb at the same solderjoints as the high amp power bus. Don't put the decoupling caps on "component carriers" and then wirerwap them into the circuit. Pullup resistors and similar stuff can go on carriers though.

[sqkybeaver]

if you will use the wire wrap technique, i suggest getting actual wire wrap perf-board with a ground plane, you have to use sockets but every pin will have a ground next to it.

[Alex555]

I have very little money, and actual wire wrap boards are expensive. I only use sockets for ICs, I just poke other components directly through the board, and often the leads are thin enough to wire wrap directly to a socket pin. I sometimes have "hybrid" wire wrapped and point to point soldered boards. I'm cheap. Often I just put caps between the chip and socket and put the cap leads in the same socket hole as the chips power lines.