A bandgap voltage reference is a temperature independent voltage reference circuit widely used in integrated circuits. wikipedia 
A Transistor Voltage Reference, and What the Band-Gap Has To Do With It, A Paul Brokaw, 1989, University Video Communications and Internet Archive.
This video took me back to my junior year of electrical engineering. I especially liked the way Brokaw explained elements of circuitry five ways.
The circuit had a name, like current mirror.
The circuit had a diagram lumping irrelevant elements.
The circuit had a formula based on physics.
The circuit had a graph from simulation.
The circuit had cause and effect told as a story.
I liked the video enough that I poked around the Internet Archive to see what else they had. Then I added the archive to sites that wiki understands. github
I wanted to explain the value of this circuitry more intuitively but still felt the need to drop the formula for current through a junction.
\( \propto (e^\frac {qV} {kT}-1) \)
This is my simplification of Brokaw and an excuse to write LaTeX for which a page of symbol names was indispensable. webpage