So here it is:

I don’t know how exactly this circuits works. I don’t understand how that feedback loop sets up an accurate know current source biasing, and what transistor is it trying to bias, Q4? For what?

With accurate current matching I presume it means that currents stay the same no matter what the voltage Vout is, but exactly what currents and why does this circuit need this? How does putting Vbias in one of the transistors in the pair differential helps this? I don’t understand.

Lets say I have code 10 as my input, so I presume d1 = 1 (or some other voltage) and d2 = 0. What happens next?