... In the “ECAL” configuration, C2b is recharged from C1 through R2e and R2b. In the
“HCAL” configuration, the return path is more difficult: as C1 is not present, charge
comes from the regulator op amp, passing through R1b, b-c junction of Q1 and then
R2e and R2b (this is the reason why in the “HCAL” ...