In the early 1970s, the Fluke company invented a revolutionary new RMS sensor integrated circuit, used to convert an arbitrary waveform into its DC-equivalent (RMS) voltage. The device uses two precision resistors to heat a pair of matched transistors connected as a differential pair:



Describe how this circuit functions. What physical principle(s) does it use to derive an RMS value for Vin? Why is it important that all identical components (transistors, resistors) be precisely matched?