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16-bits ADC anyone?

I worked with a 16-bit cirrus logic sigma-delta adc in a design with a non-linear gas sensor and 16-bits was _just_ enough. If needed, I could have gone up to the 23/24 bit device in the same footprint, for more resolution. Absolute accuracy wasn't the main issue (I could have got away with 12/13 bits for that), resolution was. I used it with an 8-bit micro.

The really good thing about the A/D, was that its programmable internal amplifiers had a gain stability against temperature of only a few ppm/degree celcius, which meant that I could get away with a cheapish reference, of about 5ppm (iirc).

Can't remember the exact cirrus part number now, but would look at those again as the price was pretty good too.

Regards,

Paul.

Reply to
Paul Taylor
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My experience was similar (except with discrete integrating ADCs [1]). Application was temperature control; we needed as much resolution as we could get, with low noise and total monotonicity (mainly for the derivative term), while absolute accuracy was somewhat less important - around 0.25% of full-scale, IIRC.

[1] By "discrete", I mean that our cost and resolution constraints didn't allow for buying in an ADC (this was some years ago). We used a couple of methods: one was the classic dual-slope integrator (where we measured time), the other was a voltage-to-frequency design (where we counted pulses).

We used the classic ratiometric approach: we used a 4-channel input mux, and measured the input signal, a reference voltage, ground, and either the cold junction for thermocouples, or the third wire for RTDs. That allowed us to characterise everything except linearity.

Bottom line was that we were achieving something like 20- to 24-bit resolution with components (in addition to the micro) costing a few tens of pence. The tradeoff, of course, was speed - these were not flash converters ;).

Steve

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Reply to
Steve at fivetrees

Steve at fivetrees expressed precisely :

Can you give me any link about this approach?

Thanks!

Reply to
djordj

Which bit: ratiometric measurement? If so, Google is your friend:

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Amongst others.

Steve

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Reply to
Steve at fivetrees

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