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US 6,297,693 B1Granted
Techniques for synchronizing a self oscillating variable frequency modulator to an external clock
AssigneeRed Chip Company Ltd.
InventorStuart W. Pullen
Life of this patent
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Abstract
The frequency spectrum of variable frequency class D modulator interferes with RF signals in the AM bandwidth. Here several techniques solve the problem including an amplifier that synchronizes an external clock input the summing node of the integrator, an amplifier that gates an external clock to the modulator using a transmission gate that responds to the AM frequency, and an amplifier that adjusts its own hysteresis to provide a clock that does not interfere with AM input signals.
Claims6
A self oscillating class D amplifier synchronized to an external clock comprising:
- an integrator with a summing input for receiving inputs from an audio signal source and analog and digital feedback signals of the amplifier output;
- a pulse width modulator for receiving the output of the integrator and a feedback signal representative of an output of the amplifier and generating a series of output pulses where the width of the pulses is proportional to the amplitude of the input audio signal;
- a bridge comprising an upper mosfet and a lower mosfet;
- level shift and gate drive circuitry coupled to the output of the pulse width modulator and to the gates of the mosfets for shifting the output level of the pulses and for driving the gates of the mosfets;
- a digital output terminal coupled to the mosfets and an inductor and low pass filter coupled to the digital output for converting the digital output into an analog signal for driving a speaker;
- and
- a transmission gate coupled to the pulse width modulator for selectively connecting an external clock signal to the pulse width modulator for controlling the output frequency of the pulse width modulator in accordance with the external clock signal.
4 more elements
A self oscillating class D amplifier synchronized to an external clock comprising:
- an integrator with a summing input for receiving inputs from an audio signal source and analog and digital feedback signals of the amplifier output;
- a pulse width modulator for receiving the output of the integrator and a feedback signal representative of an output of the amplifier and generating a series of output pulses where the width of the pulses is proportional to the amplitude of the input audio signal;
- a bridge comprising an upper mosfet and a lower mosfet;
- level shift and gate drive circuitry coupled to the output of the pulse width modulator and to the gates of the mosfets for shifting the output level of the pulses and for driving the gates of the mosfets;
- a digital output terminal coupled to the mosfets and an inductor and low pass filter coupled to the digital output for converting the digital output into an analog signal for driving a speaker;
- and
- a high pass filter coupled to the summing input of the integrator and to a square wave source for adding a square wave to the integrator input and thereby synchronizing the pulse width modulator to the input square wave.
4 more elements
A self oscillating class D amplifier synchronized to an external clock comprising:
- an integrator with a summing input for receiving inputs from an audio signal source and analog and digital feedback signals of the amplifier output;
- a pulse width modulator for receiving the output of the integrator and a feedback signal representative of an output of the amplifier and generating a series of output pulses where the width of the pulses is proportional to the amplitude of the input audio signal;
- a bridge comprising an upper mosfet and a lower mosfet;
- level shift and gate drive circuitry coupled to the output of the pulse width modulator and to the gates of the mosfets for shifting the output level of the pulses and for driving the gates of the mosfets;
- a digital output terminal coupled to the mosfets and an inductor and low pass filter coupled to the digital output for converting the digital output into an analog signal for driving a speaker;
- and
- a divider coupled to the output of the modulator and to the feedback signal of the modulator for converting the modulator output into a square wave.
4 more elements
Dependencies are inferred from the claim text.