Electronics > Metrology

HPM7177 ADC from CERN

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jaromir:
Not sure if this was discussed before, but CERN released some fresh details of one of their projects - HPM7177 ADC, including preliminary testing and paper comparing commercially available on-chip ADCs. As name suggests, this one is built around AD7177. I can see some unclear points there, but overall it's nice design with a few details to take inspiration from.

https://www.ohwr.org/project/opt-adc-10k-32b-1cha/wikis/home

niner_007:
Correct me if I’m wrong, but this is not really an ADC, but more like a DAQ system, they are using an off the shelf ADC

guenthert:
 Perhaps noteworthy is that their claimed INL error specs are lower than the published one of the ADC.  Did CERN find that AD is overly conservative, are those selected parts or do they some post-acquisition data transformation?

Kleinstein:
The actual INL can be effected by the input and reference buffering. They may have improved there over the AD reference design used for the DS.
Another point is using a nominal range that does not extend all the way to the extremes. Much of the INL looks like to be similar to an U³ part and there it helps to reduce the range a little and get some extra over-range where the INL is larger.

Driving the differential signal to the ADC is a main part of the circuit. Some of the INL error seen by AD could also come from this part and not just the ADC itself. The extra scaling (e.g. 7V from LTZ to some 5 V ref for the ADC chip and +-10/13 V input signal to a +-5 V range differential signal is quite some effort with likely custom resistor arrays.
 
It looks like they tested only few samples - they could have been lucky.
There can also be some selection check, to through out bad units.

jaromir:

--- Quote from: guenthert on February 06, 2020, 05:28:02 pm --- Perhaps noteworthy is that their claimed INL error specs are lower than the published one of the ADC.  Did CERN find that AD is overly conservative, are those selected parts or do they some post-acquisition data transformation?

--- End quote ---
They are selecting both ADCs and LTZ references (hundreds of pieces of HPM7177 to be built) to achieve needed parameters.

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