input filter capacitors

jordens commented 3 years ago

Let's lower C105, C46, C110, C53, C120, C121 from 100 nF to 10 nF to get a 1kHz corner (10+(10||10) nF and 10||(5+5) k). This is still 120 dB at the first alias. Matches the 1 kHz corner filter after the DAC (https://github.com/sinara-hw/Thermostat_EEM/issues/25).

gkasprow commented 3 years ago

Do the same in Thermostat as well?

gkasprow commented 3 years ago

done

jordens commented 2 years ago

@gkasprow

Having re-thought the filter constraints, we should apply a fix (the filter needs to take into account the NTC impedance, the aliasing requirements, the ADC bias current with resistor tempcos, ratiometric filter matching):

Sense channels (AIN*)

the first series R on the ADC channels should remain at 51R (R40, R42 etc: 4 per ADC)
the second series R should become ~2k7 (R41, R43 etc: 4 per ADC)
differential C should be 10n (C105, C46 etc: 4 per ADC)
common mode C should be 1n (C104, C106, C45, C47 etc: 8 per ADC)

Reference pair (REF+-)

first RC: 270R series, 100n diff, 10n common mode
second RC: 270R series, 100n diff, 10n common mode

filipswit commented 2 years ago

Modified:

jordens commented 2 years ago

Good. Thanks.

sinara-hw / Thermostat_EEM

input filter capacitors #31

Sense channels (AIN*)

Reference pair (REF+-)