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US 8,558,497 B2Granted
Reduced electromagnetic interference for pulse-width modulation
AssigneeCypress Semiconductor Corporation
InventorDavid G. Wright
Life of this patent
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Abstract
A method and apparatus to drive a load using a pulse-width modulated (PWM) signal and spread a spectrum of the PWM signal across a plurality of frequencies while maintaining a constant duty cycle for the load.
Claims23
A method, comprising:
- driving a load using a pulse-width modulated (PWM) signal;
- and
- spreading, by a processing device, a spectrum of the PWM signal across a plurality of frequencies while maintaining a substantially constant duty cycle for the load, wherein the spreading comprises varying a clock frequency for the PWM signal according to a spreading profile and synchronizing the variations in the clock frequency with a change in a period of the PWM signal.
An apparatus, comprising:
- a pulse-width modulation (PWM) circuit configured to drive a load using a PWM signal;
- and
- a PWM control circuit, coupled to the PWM circuit, configured to spread a spectrum of the PWM signal across a plurality of frequencies while maintaining a desired duty cycle for the load, the PWM control circuit comprising a selection circuit to vary a clock frequency for the PWM signal according to a spreading profile and synchronize the variations in the clock frequency with a change in a period of the PWM signal.
A method comprising:
- comparing a value of a counter to a duty cycle count register value, wherein the counter is clocked by a clock signal;
- varying a frequency of the clock signal and synchronizing the variations in the clock frequency with a change in a PWM period according to a spreading profile;
- if the value of the counter equals the duty cycle count register value, switching an output of a pulse-width modulation (PWM) circuit used to drive a load from a first state to a second state;
- comparing the value of the counter to a terminal count register value;
- if the value of the counter equals the terminal count value, switching the output of the PWM circuit from the second state to the first state.
2 more elements
Dependencies are inferred from the claim text.