Patent ID: 6879124

Claim:
A system for detecting Zero Crossing Points (ZCPs) of phase back EMF in a brushless DC motor having a plurality of switching signals for commutating each of a plurality of phases of said brushless DC motor, said system comprising: a ZCP level detection circuit for receiving terminal voltages of each of a plurality of phases of said brushless DC motor and a neutral voltage and for generating a ZCP level output for each of a plurality of phases of said brushless DC motor, said ZCP level output comprising a plurality of rising and falling edges corresponding to each Zero Crossing Point of a phase voltage for each of a plurality of phases of said brushless DC motor; a pulse generator for receiving said plurality of ZCP level outputs and for generating a ZCP pulse signal, said ZCP pulse signal comprising a plurality of pulses corresponding to each of said plurality of falling and rising edge of said plurality of ZCP level outputs; a first false ZCP masking signal for masking a first plurality of false ZCPs from said ZCP pulse signal and for generating a first masked ZCP signal, said first false ZCP masking signal comprises a plurality of pulses corresponding to said first plurality of false ZCPs; and a state comparator for comparing logic values of said ZCP level outputs corresponding to a plurality of pulses of said first masked ZCP signal, and for masking a second plurality of false ZCPs to generate a true ZCP signal; wherein said plurality of pulses of said ZCP pulse signal is of a first predetermined width.