In a d.c. brushless motor drive circuit, the output amplifier produces a motor winding drive current with dulled rise/fall edges from a detected sinusoidal back e.m.f. voltage induced on the winding during the steady-state operation when the motor runs at the rated speed. The output amplifier...http://www.google.ca/patents/US5818179?utm_source=gb-gplus-sharePatent US5818179 - Brushless motor drive circuit including a linear amplifier for sending an output signal based upon the detected back electromotive force voltage 
