Fave dual chopamp?

We've used a lot of (37K!) AD8628 and they have worked well.

I had to add a tiny trimpot to this board

to tweak out the last few microvolts. Nuisance.

The only chopamps I've used have been synthesized in software or firmware

-- turn off excitation, measure, turn on excitation, measure, subtract -- poof! an answer.

It takes the ADC offset out of the equation, which is nice if you're trying to find good, readily available ADCs, because it seems that all the monolithic ADCs have significant offset.

It also synchronizes the chopping noise with the measurement, meaning that you can make it go away.

This is a thermopile front end for a fire detection application, so the only way to turn off the excitation is an extinguisher. ;)

Cheers

Phil Hobbs

Thanks, I'll try that one then.

Cheers

Phil Hobbs

That's different. Although, if I were going into an ADC I'd consider chopping with an analog switch.

(And yes, I have a thing for end-to-end chopping when there's ADC's in the loop).

I've used the ADA4528-2 but it is 5V total supply voltage iirc, not +/-5

The offset voltage was impressively low in my application.

Why would that be better than the sampler in the ADC? Just offset voltage?

Not a bad plan. My preference is to make the signal phase go from 0 to pi instead of on-off, because it saves SNR.

Cheers

Phil Hobbs

Chopper wheel (mechanical) if front of the thermopile? Or some other sort of light blocking thing.

George H.

My preference, also! ...Jim Thompson

Monolithic fast ADCs just seem to have crappy offset voltages. I suspect it's the comparator in the SAR rather than the sampler itself.

I suppose my tune might be different if I were designing a system that only needed to update slowly, and there was a decent-enough ADC for the job.

Me too, if that doesn't create more problems than it solves.

Yeah, you can do that, but this has to go on a ginormo piece of heavy equipment in a very dirty environment with lots of shock and vibration.

Cheers

Phil Hobbs