Soft transitions between muted and unmuted states in class D...

Details Soft transitions between muted and unmuted states in class D... Soft transitions between muted and unmuted states in class D...

2004-10-12

2008-05-27

Nguyen, Khanh Van (Department: 2817)

Amplifiers

Modulator-demodulator-type amplifier

C330S20700P

Reexamination Certificate

active

07378904

ABSTRACT:
A class AD audio amplifier system (10) with reduced noise capability in muting and unmuting events is disclosed. The amplifier system (10) includes multiple audio channels (20), each of which can be constructed to include a pulse-width-modulator (PWM) (24). The PWM modulator (24) includes a pair of comparators (39A,39B;52+, 52−) that generate complementary PWM output signals based upon the comparison between a filtered difference signal and a reference waveform. When the system is muted, a common mode voltage (CM_RAMP) is applied to the inputs of the comparators (39A,39B;52+ 52−) to suppress the duty cycle at the amplifier output, preferably to a zero duty cycle. In the transition from a muted state to an unmuted state, the common mode voltage (CM_RAMP) is ramped from the suppressing voltage to zero common mode voltage, permitting the duty cycle of the complementary PWM signals to gradually increase, thus reducing clicks and pops. The converse operation is performed in the transition from unmuted to muted. Pulse-width-modulation control logic (26) is also included to ensure that that the PWM “on” and “off” pulses are of at least a minimum duration, and also to generate compensating pulses on the complementary PWM line at low duty cycles.

REFERENCES:
patent: 6563377 (2003-05-01), Butler
patent: 6720825 (2004-04-01), Hansen et al.
patent: 2004/0017854 (2004-01-01), Hansen et al.

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