Ripple count circuit including varying ripple threshold detection

A ripple count circuit comprising:

• an amplifier configured to amplify a drive current that drives rotation of a rotor included in a direct current (DC) motor;
• a current differential circuit configured generate a derivative current signal that indicates an instantaneous rate of current change (d(i)/dt)) of the drive current;
• a bandwidth filter configured to filter the derivative current signal based on a rotational speed (ω) of the rotor so as to output a first filtered signal;
• a downstream low pass filter configured to filter the first filtered signal based on the rotational speed (ω) of the rotor so as to output a second filtered signal that eliminates harmonics from the first filtered signal;
• a variable threshold unit configured to generate a varying threshold signal based on the second filtered signal;
• a comparator circuit configured to compare the second filtered signal to the varying threshold, and to generate a pulsed output signal having a first output voltage level when a voltage level of the second filtered signal is greater than or equal to the varying threshold signal, and a second output voltage level when a voltage level of the second filtered signal is less than the varying threshold signal,
• wherein the ripple count circuit includes a downstream low pass filter disposed downstream from a bandwidth filter, the downstream low pass filter has a varying frequency cutoff that is actively set according to the rotational speed (ω) of the rotor and configured to eliminate harmonics from the at least one filtered drive current signal,
• wherein the pulsed output signal indicates the rotational speed (ω) of the rotor and a rotational position (θ) of the rotor, and
• wherein the bandwidth filter has variable center frequency (fO) that is actively set according to the rotational speed (ω) of the rotor so as to filter the derivative current signal based on the rotational speed (ω) of the rotor.

Currently amended A method of determining a rotor speed of a direct current (DC) motor, the method comprising:

• generating a variable supply voltage;
• inducing a drive current based on the variable supply voltage, and rotating a rotor included in the DC motor based on the drive current;
• generating a mechanical force in response to rotating the rotor to drive a component;
• filtering harmonics from the drive current signal using a downstream low pass filter disposed downstream from a bandwidth filter to generate a filter drive current;
• actively setting a varying frequency cutoff of the downstream low pass filter according to the rotational speed (ω) of the rotor;
• generating a varying threshold signal based on the filtered drive current signal;
• and
• generating a pulsed output signal indicative of the rotational speed (ω) of the rotor and a rotational position (θ) of the rotor based on a comparison between the filtered drive current signal and the varying threshold signal,
• wherein filtering the harmonics from the drive current comprises performing a first filtering operation on the drive current, the first filtering operating including a bandwidth filtering operation that filters the drive current based on a varying center frequency that is actively set based on the rotational speed (ω) of the rotor.