Method and system for transitioning between operation states in an output system

This invention relates to output systems, and more specifically, to systems and methods for transitioning between operation states in an output system.

Digital techniques for audio signal processing extend to the driving of audio output amplifiers. A popular class of amplifier circuits in many audio applications is “class D” amplifiers. A Class D amplifier drives a complementary output signal that is digital in nature, with the output voltage swinging fully from “rail-to-rail” at a duty cycle that varies with the audio information. Complementary metal-oxide-semiconductor (CMOS) output drive transistors are thus suitable for class D amplifiers; as such devices are capable of high, full-rail, switching rates such as desired for digital applications. CMOS drivers conduct low DC current, and their resulting efficiency is especially beneficial in portable and automotive audio applications. In addition, the ability to realize the audio output amplifier in CMOS enables integration of an audio output amplifier with other circuitry in the audio system, further improving efficiency and also reducing manufacturing costs of the system. This integration also provides performance benefits resulting from close device matching between the output devices and the upstream circuits, and from reduced signal attenuation.

As is known in the art, an undesirable effect of a transient signal can exist in the output of a class D amplifier. The transient signal can cause audible artifacts, such as a “click/pop” noise, an audible “humming” noise or a crunching sound. Typically, the transient signals occur when the class D amplifier changes states of operation, such as between an activated state (e.g., switching mode or steady state) and a deactivated state. Reduction (or elimination) of such undesirable transient signals is thusly needed.

One aspect of the invention is related to a closed loop amplifier system comprising a modulator that provides a pulse-width modulated (PWM) output signal based on an input signal, the modulator having a variable closed loop transfer function. The system also comprises a ramp generator that provides a ramp signal to the modulator, the variable closed loop transfer function of the modulator varying as a function of the ramp signal. The system further comprises a controller that controls the ramp generator to provide the ramp signal to adjust the variable closed loop transfer function during transitions between operating states of the amplifier system.

Another aspect of the invention is related to a system for transitioning an operation state of a multi-channel system, the system comprising means for providing a ramp signal and means for controlling the means for providing the ramp signal. The system also comprises means for providing a plurality of pulse-width modulated (PWM) signals that includes a means for filtering according to a transfer function that varies as a function of the ramp signal, wherein each of the plurality of PWM signals includes a P-side signal and an N-side signal associated with a respective channel that varies based on an input signal and the ramp signal. The system further comprises means for amplifying the plurality of PWM signals and providing a feedback signal to the means for providing the plurality of PWM signals. The system still further comprises means for transitioning the means for providing the plurality of PWM signals between at least two operation states based at least in part upon the ramp signal.

Still another aspect of the invention is related to a method for transitioning between an activated output state and a deactivated output state of a modulator of an audio system. The method comprises monitoring a selection signal, the selection signal indicating a change in the output state of the modulator. The method also comprises varying a closed loop transfer function of the modulator as a function of the ramp signal in response to detecting the selection signal indicating the change in the output state of the modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system in accordance with an aspect of the invention.

FIG. 2 illustrates an example of an audio channel in accordance with an aspect of the invention.

FIG. 3 illustrates an example of a modulator in accordance with an aspect of the invention.

FIG. 4 illustrates another example of a modulator in accordance with an aspect of the invention.

FIG. 5 illustrates an example of a voltage controlled variable resistor in accordance with an aspect of the invention.

FIG. 6 illustrates an example of a clip detector in accordance with an aspect of the invention.

FIG. 7 illustrates an example of ramp signals in accordance with an aspect of the invention.

FIG. 8 illustrates a gain diagram of a modulator in accordance with an aspect of the invention.

FIG. 9 illustrates a phase diagram of a modulator in accordance with an aspect of the invention.

FIG. 10 illustrates an example of a multi-channel system in accordance with an aspect of the invention.

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