a current-to-voltage converter, also called a resistor,
@Felthry Wait what? *blinks, earfocuses*
@IceWolf well, an ideal resistor has a voltage across it that is equal to its resistance times the current through it. Thus, it takes a current as input and produces a voltage as output, though its output characteristics are pretty terrible so proper I-to-V converters tend to use an in-amp as well to increase input impedance and decrease output impedance, and to level-shift if necessary.
@IceWolf Almost all high-bandwidth current sensors are based around passing the current to be sensed through an extremely precise resistor of the lowest resistance possible (to not disturb the circuit too much) and measuring the voltage across that with a high-bandwidth amplifier and ADC. Magnetic current sensors like current transformers and Hall-effect sensors have less of an impact on the circuit, but are limited in bandwidth compared to the resistive type due to magnetics being messy
@IceWolf (it actually is fun though since you can use the nonlinearity to produce a magnetic amplifer that uses nothing but a ferrite core and some wires, you can control the amplitude of a high-frequency signal on one winding by applying a low-frequency signal on another winding that's just enough to partially saturate the core)