Dual mode class D amplifiers
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United States of America Patent
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Jul 1, 2003
Grant Date -
N/A
app pub date -
Jun 29, 1999
filing date -
Dec 22, 1998
priority date (Note) -
Expired
status (Latency Note)
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Abstract
Pulse width modulated ('Class D') amplifiers and controllers switching in the 50 khz to 2 MHz range generate harmonics which interfere with AM radio reception. This has precluded wide spread acceptance of class D amplifiers in products with an AM radio. The amplifiers described here use a modified modulation technique when operating with an AM radio to avoid generating harmonics at the receiver selected frequency or its intermediate (IF) frequency. One embodiment uses a harmonic avoidance modulator. A second embodiment uses two or more oscillators and tests for the least distorted output signal. A third embodiment switches the mode of operation to a class AB amplifier when an AM signal is amplified.
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