Kok Khuan P'ng

We connects 2651A to 0.75V voltage rail with 12A maximum output current.
We have several questions:
1. The transition from quadrant-4 to quadrant-3 is seamless when the load current is rising from 0 to 12A?
2. What is the internal resistance or transition point between quadrant-3 and -4?

Taking sink current (source negative current) 12A as an example, assuming the sink current internal path resistance as 10mOhm (R1=R2=R3=R3=R4=R5=2mOhm as shown in attachment), the voltage drop across all these internal resistance is 0.12V (12A x 10mOhm), which is the minimum operating voltage for 12A sink current. If my DUT provides a voltage lower than 0.12V (due to long cable) to FORCE HI and FORCE LO ports, 2681A would not be able to sink 12A. The most it can sink is 10A if 0.1V appears on FORCE HI and FORCE LO ports.

May we know how SourceMeter analog architecture is different from Eload?
If I am not mistaken, SourceMeter also use MOSFET to provide source and sink current and sense resistor to sense the current accurately. Of course, SourceMeter use PCB to have component mounted on it. Either PCB, MOSFET or sense resistor will have higher voltage drop across themselves with higher sink/source current.

Attached an example of Min Operating Voltage from Keithley Eload here.