Driving an ADC

Other Hardware General Electronics
1

Hi all,

I'm building a transimpedance photodetection circuit that feeds into a 16 bit (SAR) ADC, ADS8341. I'm not too familiar with how the ADC needs to be driven (short of just simply hooking up the op amp's output to the ADC input).

Can anyone familiar with this topic give me a few basic pointers of things to consider?

Thanks in advance!

2

Not sure what you mean by "driven" - do you mean the electrical input or the software to read results.

For the latter:

page 12.

3

Yes, the electrical input....

4

Well, telling us some more about the "transimpedance photodetection circuit" would help.

5

At present I have a few potential circuits to use, though as the project has evolved I've recognised limitations for some of them.

Currently, I've two on the go:
http://picpaste.com/LTC54-N5edf2bn.jpg

And I'm also considering running the output from the above circuit into this synchronous detection circuit:
(I'm measuring a modulated LED circuit and want to get rid of any ambient light sources, so the clock input is sync with the LED switching on and off)
http://picpaste.com/sync-circuit-5AKqhRnN.jpg

In both cases the output is the output of an op amp. Can I simply connect this straight up to the input channel of the ADC? What are the general rules for SAR ADCs? I recall that when such ADCs samples it creates a charge transient at the input (due to the switching of the ADC sampling cap) and therefore interferes with the amplifier output. Will just a single pole RC filter between the op amp and ADC suffice?

Any info would be much appreciated! Thanks!

6

Firstly this is a sample-and-hold ADC (they pretty much all are these days!) so transients aren't an issue for you - and driving directly by opamp means your source will be low-impedance so no input-impedance offsets to worry about.

You might want some low-pass filtering anyway to reduce noise (but you need to know the bandwidth of your signal and any LPF needs to have minimal phase distortion over the band of interest)

Look up "lock-in detector" in "The Art of Electronics" I believe for more inspiration.