Here is a video review of the AS5040 magnetic rotary encoder IC. The maker of this video connected a scope to the output of the AS5040 IC, and demonstrates how the phase of the signals changes in relation to the angle of the magnetic field. We loved the LEGO-based rig.
Demo of an evaluation board for the AS5040, showing analog PWM output, quadrature outputs, and digital data output interfaced with an Arduino. Code for Arduino available here: http://madscientisthut.com/forum_php
Via the forum.