It can be LM108 and LM112 (internally compensated) and there is admittedly no trick there. It's 1nA input bias which is rather steady with temperature as for most bipolar opamps for the reason that β actually enhances with temperature. Afterwards iterations like LT1008/LT1012 or OP97 pushed it all the way https://low-noiseamplifier33433.webdesign96.com/34668969/the-basic-principles-of-pin-diode-switch