Patent ID: 6084364
Filing Date: 2000-07-04
Classification: H02P

Abstract:
A circuit for measuring a time period between detection of zero crossings of a back electromagnetic force (bemf) signal in a polyphase direct current (dc) motor, the circuit comprising:a counter operable for counting in response to a detection of a first zero crossing of the bemf signal, and operable for outputting a count from the counter in response to a detection of a second zero crossing of the bemf signal, the count representing the period between the first and second zero crossings, and the counter having a clock input receiving a clocking signal for clocking the counter; anda first circuit for receiving a first clock signal having a first frequency and a second clock signal having a second frequency and coupling the first clock signal to the clock input of the counter in response to the motor operating at a first operating state and coupling the second clock signal to the clock input in response to the motor operating at a second operating state.