One of the answers in this question says: “Having an ADC that has better resolution than the external signal noise is a waste of money.”
I want to illustrate and understand what is meant here. So for clarity I tried to ask by using the following figures:
Above in Fig1 random noise in color red imposed on a constant input signal where the peak to peak is 1mV as shown in the figure. And in Fig1 the ADC has a resolution of 1mV. In Fig2 however the same input now goes to an ADC which has a resolution of 0.3mV.
Does that mean for this input any ADC with resolution Δ<1mV is redundant? What could be the minimum adequate resolution?
Imagine the 1mV peak to peak superimposed random noise is always the case. And the signal is coming from any voltage source with a sensitivity of 0.5mV. So there are two things here. One is the sensitivity of the source like force transducer sensitivity and the other is the random noise I showed in red.
Considering all these I cannot make reasoning what limits what along with ADC resolution.