voltage reference distribution / multiple ADCs

[rounin]

Hi all,

I'm trying to make DAQ with 4 simultaneous differential sampling channels, using 4x analog devices 24bit AD7175-2, and either a MAX6220 or MAX6126 5V reference, with the hope of getting maybe 19-20 noise free bits the first go-around. I'm planning to use a PGA280 as the input amplifier.

Is it possible to have all the ADCs share 1 voltage reference? Would they need to be separately buffered? Is it easier just to use a seperate 5V reference per ADC? (I'll be calibrating the channels separately anyway, so not too worried about a little bit of offset between them). It seems simpler to just use a reference per ADC, but if I can avoid that without causing a bunch of other layout headaches, it would be nice.

Anyone ever distributed voltage references across a board?

[Kleinstein]

The mentioned ADC has differential inputs for the reference and internal buffers for the reference too. So there should be no problem just wiring the ref. inputs in parallel. Filtering / noise reduction at the reference might be a good idea with such fast ADCs.

[rounin]

OK cool, I'll hook the REF inputs up in parallel, and look into filtering. Thanks

[ebclr]

May be this IC will cleanup your design

http://www.ti.com/product/ads1274

[rounin]

Interesting. I had also been considering the AD7768-4, and was drawn to the 7175-2 for possibility of sub uV noise at low sample rates, if everything else gets to that point.

The ads1274 looks interesting, seems to have similar performance at high sample rates? I'll dig through the datasheet some more. It looks like the settling time might be longer on the ads1274, I guess due to the deeper digital filter.

[ebclr]

Note  that AD works in parallel at the same time, this means you will have all 8 channels sampled at the same time with 8 independent adc inside the chip. That's the main point on this chip