Increased digital spindle motor control resolution through dither
First Claim
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1. A motor controller for providing pulse width modulated drive signals to a motor, the motor controller comprising:
- an input for receiving a digital demand code for controlling motor speed;
a dither generator for generating a digital dither value;
an adder for generating a dithered demand code equal to a sum of the dither value and the demand code;
a position determining circuit for determining a rotational position of the motor; and
a pulse width modulation controller for generating pulse width modulated drive signals having duty cycles controlled as a function of a stored set of waveform coefficients, the dithered demand code, and the rotational position of the motor.
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Abstract
A motor controller provides pulse width modulated drive signals to a motor. A digital demand code for controlling motor speed is input to the motor controller. A dither generator generates a digital dither value, which an adder adds to the demand code to generate a dithered demand code. A position determining circuit determines a rotational position of the motor. A pulse width modulation controller generates pulse width modulated drive signals with duty cycles controlled as a function of a stored set of waveform coefficients, the dithered demand code, and the rotational position of the motor.
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Citations
22 Claims
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1. A motor controller for providing pulse width modulated drive signals to a motor, the motor controller comprising:
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an input for receiving a digital demand code for controlling motor speed; a dither generator for generating a digital dither value; an adder for generating a dithered demand code equal to a sum of the dither value and the demand code; a position determining circuit for determining a rotational position of the motor; and a pulse width modulation controller for generating pulse width modulated drive signals having duty cycles controlled as a function of a stored set of waveform coefficients, the dithered demand code, and the rotational position of the motor. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for generating a pulse width modulated signal for driving a motor, the method comprising:
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determining a rotational position of the motor; obtaining a waveform coefficient corresponding to the rotational position of the motor; generating a digital dither value; adding the digital dither value to a digital demand code for controlling a rotation rate of the motor to obtain a dithered demand code; and multiplying the waveform coefficient by the dithered demand code to obtain a duty cycle control signal for controlling a duty cycle of the pulse width modulated signal. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A controller for controlling a rotation rate of a spindle motor, the controller comprising:
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a period measurement circuit for determining an electrical period of the spindle motor; a state machine for dividing the electrical period of the spindle motor into a plurality of commutation states; a look up table addressable by the state machine for providing a waveform coefficient for each of the plurality of commutation states; a dithered demand generator for generating a dithered demand code by adding a dither value to a received digital demand code indicative of a desired rotational speed of the motor; a multiplier for generating a duty cycle control signal equal to a product of the waveform coefficients and the dithered demand code; and a pulse width modulator for generating a pulse width modulated drive signal for the motor driver circuit, the pulse width modulated drive signal having a duty cycle defined by the duty cycle control signal. - View Dependent Claims (15, 16, 17, 18)
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19. A pulse width modulator for generating a pulse width modulated signal, the pulse width modulator comprising:
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a state machine for sequencing through a plurality of states; a look up table for outputting a digital waveform coefficient as a function of a current state of the state sequencer, wherein the look up table contains a digital waveform coefficient for each of the plurality of states; an adder for generating a dithered gain adjust code by adding a digital dither value to a digital gain adjust code; and a multiplier for generating a duty cycle control signal equal to a product of the output waveform coefficient and the dithered gain adjust code. - View Dependent Claims (20, 21, 22)
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Specification