There are no strict requirements on the shape or exact position of the transition, however in the linear region (B > 2.5V), the curve should be precise.
Below is a circuit for a regular difference calculator (OUT = A - B); is there a simple way to modify this in order to achieve the desired effect? I was thinking of employing a diode to achieve the nonlinear effect, but I'm at loss on exactly how to proceed.
I'm using a rail-to-rail output, over-the-rail input amplifier, and have no requirements on the input/output impedance of the circuit. I have all sorts of positive reference voltages and supply rails available, should those be necessary.
I need this circuit as the feedback loop of a switching + linear voltage regulator; A must be about B + 0.8V to compensate the linear regulator's drop, so feedback = A - B would suffice. However, the linear regulator requires at least 1.4V to run, thus the max(B, 2V) requirement.