Method and apparatus for measuring speed of a brush motor

A system for determining motor speed of a brush DC motor in an apparatus, comprising:

• sensing circuitry for sensing current in the brush DC motor;
• a first filter for receiving a substantially low frequency portion of the sensed current and parameters corresponding to the brush DC motor, for calculating a speed estimate thereof;
• an adaptive bandpass filter having a center frequency corresponding to the speed estimate of the first filter, for receiving the sensed current and substantially isolating a first periodic current fluctuation thereof;
• a frequency detect block for determining a frequency of the first periodic current fluctuation, a frequency of the first periodic current fluctuation corresponding to motor speed of the brush DC motor;
• and
• a tracking frequency selection block coupled to the sensing circuitry for selecting a frequency component of the sensed current and providing the selected frequency component to the first filter, wherein the speed estimate is based in part upon the selected frequency component.