Transistor operating region - push pull & current mirror
1) Push-Pull is complementary Emitter Follower, unity gain , linear mode but hFE is still dependent on Ic and Vce with a wide tolerance.



2) With a BJT current mirror, one acts with BC shorted as a diode so the voltage drop can be estimated and that collector current is thus matched for the same Vbe mirror.  Those base voltages are deterimined with R values and Vcc for that diode which is matched to the Vbe of the transsitor.