Amplifiers – Modulator-demodulator-type amplifier
Patent
1994-03-30
1995-03-14
Mullins, James B.
Amplifiers
Modulator-demodulator-type amplifier
330251, H03F 338
Patent
active
053980034
ABSTRACT:
An open-loop speaker amplifier and a dynamic range reduction circuit are disclosed. The speaker amplifier includes a bridge driver and a bridge circuit. The bridge circuit includes a first set of switches and a second set of switches. When the first set of switches are activated, a positive current flows through a speaker load. When the second set of switches are activated, a negative current flows through the speaker load. The bridge driver generates a pulse width modulated signal and a delayed pulse width modulated signal to drive the first and second set of switches of the bridge circuit responsive to a modulation signal. The modulation signal may be, for example, a plurality of pulse code modulated samples representing sound. The dynamic range reduction circuit modifies a selected signal to reduce the dynamic range of the sound reproduced based on the modulation signal. The selected signal is either the modulation signal or a reference signal. In one embodiment, the dynamic range reduction circuit modifies the selected signal by processing the selected signal based on a smooth saturating function. In another embodiment, the dynamic range reduction circuit modifies the amplitude of the reference signal based on an envelope size of the modulation signal.
REFERENCES:
patent: 4489222 (1984-12-01), Lusignan
patent: 4773096 (1988-09-01), Kirn
patent: 5077539 (1991-12-01), Howatt
Austin Steven E.
Heyl Lawrence F.
Apple Computer Inc.
Mullins James B.
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