For the example

test_comparator.sch

is there a book, paper or video reference for describing the circuit operation?

I don't know if there is a specific example of this comparator in a book. However the circuit consist of a Transconductance rail-to-rail input, rail-to-rail-output operational amplifier (red), followed by two gain stages (green). This circuit is used as a comparator, so small differences in the input should produce either '1' or '0' on the output. the violet part is the calibration circuitry. It works by ensuring all stage outputs (OUTDIFF, SAOUTF, SAOUT) are kept at ~ VCC/2 when differential input is 0. When calibration is finished the calibration transmission gates are opened and the correction voltage is stored into the 3 calibration capacitors. Basically the calibration inverters inject or sink some small current from the comparator differential/gain stages to make them perfectly balanced, even if there are device mismatches.

Great - I had interpreted it correctly, roughly speaking. I wondered why the input opamp was structured that way - thanks for the tips. I need to do a bit more ciphering but I'm well on the way now thanks again.