A portable electronic device having a speaker module is provided. The speaker module includes: a speaker unit; a back chamber; an acoustic region coupled between the speaker unit and the back chamber; and a porous material at least partially filling a portion of the front chamber, the back chamber, or the channel, for improving and extending bass performance and relieving a acoustic effect caused by the acoustic region coupling the speaker unit and back chamber. Moreover, the portable electronic device is advantageously able to compensate a resonance degradation caused by the porous material.

A scheme is described to switch the power supply to the MEMS microphone on and off in a cyclic manner that is synchronized with the associated ADC sampling rate. In this way the MEMS microphone amplifier, whether it is a J-FET transistor or an operational amplifier, is off most of the cycle time, and is turned on only for a few micro-seconds prior to the sample-and-hold timing of the ADC device. By this method, the average power consumption of an existing analog MEMS microphone can be reduced by a factor of 10 or more.

Audio transmitter circuitry is disclosed that is configurable into different modes by the user, and can output either a differential or single-ended audio signal on two signal wires. Depending on the mode, the transmitter deals with noise on the signal wires by adjusting the input resistance that such noise sees looking into the transmitter. If the transmitter is configured in a differential mode, the input resistance looking back into the transmitter from the perspective of the noise on both signal wires is relatively high. If the transmitter is configured in a single ended mode, the input resistance of noise looking back from the active signal wire into the transmitter is relatively low, to in effect ground such noise back into the transmitter, without significantly presenting such noise to the receiver.

A group-aware, current limited amplifier system including a group brownout control bus and a number of current-limited amplification channels coupled to the group brownout control bus. In an example embodiment, each current-limited amplification channel includes an amplifier, an amplifier power supply developing a current level signal that represents the amount of current being drawn by the amplifier, a brownout controller responsive to a digital audio input, the group brownout control bus, and the current level signal, and operative to develop a control signal; and an audio digital-to-analog (D/A) converter responsive to the digital audio input and to the control signal and operative to develop an analog audio output that is coupled to an input of the amplifier.

A method of audio signal processing includes receiving a first audio input signal (first input signal) at an input of a first integrating amplifier of a first single-ended (SE) closed loop channel, and second input signal with a polarity reversed relative to the first input signal at an input of a second integrating amplifier configured of a second SE closed loop channel. During audio signal processing a common-mode (CM) reference voltage level applied to a current source coupled to an input of the first and second integrating amplifiers is dynamically changed including whenever a level of the input signals is below a predetermined low level, reducing the CM reference voltage level for implementing low duty cycle (LDC) PWM operation, and whenever the level is above a level that corresponds to an onset of clipping, increasing the CM reference voltage level for at least reducing the clipping to lower crossover distortion.

Embodiments of the disclosure may include a method and apparatus for improving the efficiency and extending the operation time between recharges or replacement batteries of a portable audio delivery system. The audio delivery system may include a processor, an audio processing device, a speaker, and a rechargeable power source. The audio delivery system is generally configured to generate and/or receive an audio input signal and efficiently deliver an amplified, high quality audio output signal to a user. In some embodiments of the disclosure, the audio processing device of the audio delivery system may include a switch mode power supply (SMPS), a signal delay element, an envelope detector, and a switching signal amplifier.

A multi-channel Class D audio amplifier is provided to substantially reduce channel-to-channel crosstalk by employing in each channel a local triangle ramp generator controlled by a single global digital timing signal. The noise critical timing/integrating capacitor for the triangle ramp generator resides locally in each channel and adjacent to the PWM comparator of that channel and referenced to the local ground of that channel. The amplifier can also include a duty cycle limitation circuit to limit output power availability depending on the impedance of any attached loads (speakers).