I am trying to design a circuit that measures the current drawn by the output load and mirrors that current somewhere else. The idea is shown in the figure where we have an amplifier driving the load. We want to measure the current that flows through this load and then mirror that current somewhere else. Does anyone have an idea how to do this using current sensing?
EDIT: I forgot to mention that this is for integrated circuits that uses CMOS and the load is not grounded.
Assuming Vsource is always positive, here's a circuit commonly seen in power supplies:
simulate this circuit – Schematic created using CircuitLab
The opamp acts to keep the voltage drops across R1 and R2 equal, which means that $$I_{mirror} = \frac{R1}{R2}I_{load}$$ Imirror also flows through R3, where it can be used to turn the mirror current into a ground-referenced voltage.
Note that OA1 needs to have rail-to-rail inputs and outputs, or else have its own power supplies. And of course, the total voltage across R2, Q1 and R3 needs to be less than Vsource.
An amplifier and two Hall effect sensors would do it; sense load current with sensor #1, amplify the difference between sensor #1 and sensor #2 with the operational amplifier output directed through (sensed by) sensor #2.
If this were an AC problem, current transformers would be suitable sensors.
