Method and apparatus for frequency modulating a periodic signal of varying duty cycle
OwnerDan Ion Hariton, Narendar Venugopalinventors
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Abstract
A method and apparatus for frequency modulating a PWM involves 1) generating a high frequency carrier signal much greater in frequency than the PWM signal; 2) modulating the high frequency signal to generate a spread spectrum carrier signal; and, 3) retiming a PWM signal with this high frequency SS carrier signal so that the binary transitions of the PWM signal are aligned with the frequency varying carrier signal. In another embodiment, a PWM oscillator is driven by a second, FM oscillator having spread spectrum characteristics. In another embodiment a PWM oscillator is driven and modulated by a counter/frequency divider comprised of modules.
Claims17
An apparatus for frequency modulating a pulse width modulated signal, including:
- a first oscillator component having a first bi-directional charge pump with an output connected to hysteresis comparator means, a first feedback loop connecting the output of said hysteresis comparator means to an input of said first bi-directional charge pump, said output of said hysteresis comparator means comprising a pulse width modulated signal;
- a second oscillator component connected to an input of said first bi-directional charge pump, a second feedback loop connected from said output of said hysteresis comparator means to an input of said second oscillator component, whereby said second oscillator component is arranged to generate a spread spectrum modulation signal that drives said first oscillator component to generate a spread spectrum, frequency modulated pulse width modulated output;
- wherein said second oscillator component includes a second bi-directional charge pump having an output connected to said first bi-directional charge pump as an oscillator bias current.
A method for frequency modulating a pulse width modulated signal, including the steps of:
- providing a first oscillator component having a first bi-directional charge pump with an output connected to hysteresis comparator means, connecting a first feedback loop from an output of said hysteresis comparator means to an input of said first bi-directional charge pump so that said output of said hysteresis comparator means comprises a pulse width modulated signal;
- connecting a second oscillator component to an input of said first bi-directional charge pump, connecting a second feedback loop from said output of said hysteresis comparator means to an input of said second oscillator component, whereby said second oscillator component is arranged to generate a spread spectrum modulation signal that drives said first oscillator component to generate a spread spectrum, frequency modulated pulse width modulated output;
- wherein said second oscillator component is provided with a second bi-directional charge pump having an output connected to said first bi-directional charge pump as an oscillator bias current.
Dependencies are inferred from the claim text.