Good day ladies and gentlefreaks,
I have used a common, or garden variety, method of 2-point linear calibration for ADC inputs on many projects in the past and it has served me well. Now I find the old grey matter is a bit stretched to apply the same, or similar, technique for AC coupled inputs. With AC coupling I cannot simply apply a (DC) calibration source to the input at each of the 2 cal levels and take the readings as they will settle back to (say) half-rail or zero reference point.
I was considering applying a known AC signal level (at appropriate frequency to pass thru the analog front-end) and use the system's calculated level as a single point (the system does perform an rms calc anyway). Perhaps 2 points are still required but I figured if all is linear (and believe it should be if well within the pass-band) a 2nd point would only give me the same information.
Or instead is it necessary to inject the 2 DC levels (old style 2-point cal) at a test-point downstream of the AC coupling?
Not sure if I'm on the right track here or thinking about it in completely the wrong way.
Can anyone provide any direction/guidance/experience?