New to ADC's, newbie question

Hello,

I have a project I'm working on where I need to interface 12 sensors to an ADC.... these sensors need to be sampled as 500k samples per second.... I've found some ADC's on mouser that have 12 inputs at 1MSPS.... but what I'm not clear on is, do I have to divide that 1MSPS by 12, cause I have 12 things connected to it (in which case I need to keep looking cause that's only 83.3k samples per second) or when they say it's a 1MSPS ADC is that for all the channels?

Much thanks!

Yes you do, it's not 12 ADC's, it's ONE ADC with a switch between the 12 inputs.

You're looking at 6,000,000 samples per second, at least - it doesn't sound a trivial task.

Darn. would the solution then be to find a faster ADC.... of say 20MSPS, and then MUX my 12 inputs before feeding it into the ADC? That way I would be dividing my channels by the 20MSPS, which would give me roughly 1.8KSPS.... would this be the right approach?

thanks!

Another solution is to dedicate a slower ADC per sensor, and then do the multiplexing on the digital values.

Yes, either way would work - but you've also got to consider the huge amount of data that's arriving, and what you're going to do with it - a processor solution is going to require a VERY fast processor.

hmmm... well if I did have 500KSPS ADCs.... and then I sent their outputs to a mux...for a 1 sample burst of data from them.... my MUX would have to scan the channels pretty dern quick wouldn't it... basically greater than 6MHz, to catch all that data that's basically arriving in parrallel at my MUX inputs and changing at 500Hz at each input.... then my MUX would output this info to a processor who would probally have to do something fancy to parse the 12 channels worth of data from a single line.... this is getting complicated. But does this sound like the right track?

That should work in theory. I agree that an ADC for each channel is a better approach, since muxing analog data at 500kHz requires very careful analog design techniques to minimize switching noise in the analog signals. Digital signals just love to contaminate nearby analog signals.

Edit: If you have bursts of data, you might want to consider storing them directly into memory using a DMA approach, and then processing the data from the memory between bursts.

I would investigate a turn-key solution. There are PC-based Data Aquisition systems (hardware and software is included) that do what you want. However, they are not Cheap (for a good reason). If you are doing this at work, you will spend much more doing it yourself than the cost of a turn-key solution. If you are doing this as a hobbyist, only you know what your time is worth...