QUESTION:
What is the minimum voltage that the current source needs across it to maintain a more or less constant current, by analyzing the LTspice plots for the circuits?
ANSWER:
Considering the LTspice plots provided in the activity, with sink tied to negative supply:
And sink tied to positive supply:
We may notice that in both cases the current becomes more or less constant after reaching a voltage around 0.8-0.9V.