Timeline for High resolution ADC vs amplifiers

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Nov 18 '18 at 3:50 comment added analogsystemsrf @ Scott Seidman Was the "square wave" square, or did it have lots of droop, which indicates a high-pass-filter effect, where the aggressor energy comes thru a metal-air-metal path? One way to model paths thru the air is to use a parallel-plate equation, where C = 8.9pF/meter * Area/Distance, and then scale down by 1/distance^3 because the underlying PLANES will capture most of the Efield flux. The displacement current is converted back to voltage, because the charge has to exit the node thru any/all available resistances (impedances) to get back home. How far away was the LED/resistor/driver?
Nov 13 '18 at 15:32 comment added Scott Seidman ... all design considerations that never come up until you start using high^2 res ADC's. My signals are generally orders of magnitude above the square wave magnitude, which would just simply ordinarily disappear into the noise.
Nov 13 '18 at 15:28 comment added Scott Seidman @analogsystemsrf -- absolutely all very good questions, and all very difficult to answer, as the square wave was calculated to be 11\$\mu\$V on the input of my on-chip PGA! In the next iteration, I changed the side of the isolation barrier that the dev board was on, and left the ADC on the side with the low-noise instrumentation amp. By the time I was done, I had my noise level <1\$\mu\$V rms.
Nov 13 '18 at 14:46 comment added analogsystemsrf @ Scott Seidman Thus the Power Supply Rejection was poor? Wondering how the "Sag" was affecting the conversion. Or was the Electric Field of the LED cathode, where the square-wave existed, coupling into the high-impedance bio-potential wiring?
Nov 9 '18 at 20:04 history edited Scott Seidman CC BY-SA 4.0
added 343 characters in body
Nov 9 '18 at 19:59 history answered Scott Seidman CC BY-SA 4.0