A brushless DC (BLDC) generally does not have a sinusoidal signal it has two out of its three windings energised at one time, although it resembles an AC sinusoidal motor in construction.
An AC sinusoidal can actually be run as a BLDC.
http://users.tinyworld.co.uk/flecc/4...otor031102.swf
If you use the step mode, you can observe the sequence.
Also a Brushed motor can be run on SCR drives rather than PWM as this was the earlier form of control before PWM became popular.
KB and Baldor still make SCR controllers.
An AC servo motor is classed as a synchronous motor, An AC induction motor although dependent on frequency, is not synchronous.
Al.