A portable audio device may be configured to measure load characteristics of headphones. The device may measure direct current (DC) and/or alternating current (AC) characteristics of the load. These characteristics may be measured by an audio component, such as an audio codec chip or integrated circuit (IC) controller, and reported to software or firmware executing on a processor coupled to the audio component. The software or firmware may then take action based on the measured load characteristics. For example, the load characteristics may be compared to a database of headphones and their known load characteristics to determine a particular headphone model or type of headphone attached to the audio output. The processor may then apply an appropriate equalization curve.

A portable audio device may be configured to measure load characteristics of headphones. The device may measure direct current (DC) and/or alternating current (AC) characteristics of the load. These characteristics may be measured by an audio component, such as an audio codec chip or integrated circuit (IC) controller, and reported to software or firmware executing on a processor coupled to the audio component. The software or firmware may then take action based on the measured load characteristics. For example, the load characteristics may be compared to a database of headphones and their known load characteristics to determine a particular headphone model or type of headphone attached to the audio output. The processor may then apply an appropriate equalization curve.

In accordance with an embodiment, a circuit includes a low noise amplifier transistor disposed on a first integrated circuit, a single pole multi throw (SPMT) switch disposed on a second integrated circuit, and a bypass switch coupled between a control node of the low noise amplifier transistor and an output node of the low noise amplifier transistor. The SPMT switch couples a plurality of module input terminals to a control node of the low noise amplifier transistor, and the bypass switch including a first switch coupled between the control node of the low noise amplifier transistor and an intermediate node, a second switch coupled between the intermediate node and the output node of the low noise amplifier transistor, and a third switch coupled between the intermediate node and a first reference node. The first integrated circuit and the second integrated circuit are disposed on a substrate.

A method of operating a headphone configured to be removed from and placed in close proximity to a user's ear can include generating an input signal by an input signal generating device. The method can also include determining whether an insertion event has occurred based on the generated input signal and causing the headphone to operate in 5 a low power mode responsive to an absence of an insertion event determination after a first period of time. The method can also include causing the headphone to operate in an ultra-low power mode responsive to the absence of an insertion event determination after a second period of time that occurs after the first period of time, the ultra-low power mode having a lower power consumption than the low power mode.

A supply voltage conditioning circuit comprises a differential amplifier, a comparator, a sample and hold (S/H) circuit, and a delay circuit. The differential amplifier receives an input supply voltage and a reference voltage, and outputs a difference signal. The comparator receives the difference signal and a value representative of a noise margin, and outputs a control signal indicative of whether the difference signal is greater than the value representative of the noise margin. The S/H circuit samples the input supply voltage in response to the control signal indicating the difference signal is greater than the noise margin, and outputs a substantially noise free supply voltage. This allows the output supply voltage to track underlying changes in the input supply voltage but filter out noise in the input supply voltage. The delay circuit receives and delays the output supply voltage to generate the reference voltage.

A supply voltage conditioning circuit comprises a differential amplifier, a comparator, a sample and hold (S/H) circuit, and a delay circuit. The differential amplifier receives an input supply voltage and a reference voltage, and outputs a difference signal. The comparator receives the difference signal and a value representative of a noise margin, and outputs a control signal indicative of whether the difference signal is greater than the value representative of the noise margin. The S/H circuit samples the input supply voltage in response to the control signal indicating the difference signal is greater than the noise margin, and outputs a substantially noise free supply voltage. This allows the output supply voltage to track underlying changes in the input supply voltage but filter out noise in the input supply voltage. The delay circuit receives and delays the output supply voltage to generate the reference voltage.

An audio amplifier and a warning sound amplifier are connected in parallel to each other, relative to a voice coil of a loudspeaker. A resistor having an impedance greater than an impedance of the voice coil is connected to the voice coil and is also connected to the warning sound amplifier. An audio signal from the warning sound amplifier is input to the voice coil via the resistor. Thus, since the warning sound amplifier is connected to the resistor having the impedance greater than the impedance of the voice coil of the loudspeaker, even in a case where only the audio amplifier is operated, a large current is prevented from flowing into the warning sound amplifier.

An audio amplifier and a warning sound amplifier are connected in parallel to each other, relative to a voice coil of a loudspeaker. A resistor having an impedance greater than an impedance of the voice coil is connected to the voice coil and is also connected to the warning sound amplifier. An audio signal from the warning sound amplifier is input to the voice coil via the resistor. Thus, since the warning sound amplifier is connected to the resistor having the impedance greater than the impedance of the voice coil of the loudspeaker, even in a case where only the audio amplifier is operated, a large current is prevented from flowing into the warning sound amplifier.

Systems and methods for protecting a loudspeaker from excessive excursion include an audio source, an adaptive excursion protection filter, an audio clipper, an inverse excursion protection filter, an amplifier and a loudspeaker. The system performs operations including receiving an audio signal, applying an excursion protection filter, the excursion protection filter adapting in real-time to one or more speaker conditions, clipping the audio signal, applying an inverse excursion protection filter, and amplifying, using an amplification circuit, the audio signal for output to the speaker.

A preamplifier amplifies signals input to first and second input terminals. A first switching circuit receives first and second input signals and outputs those to the first and second input terminals. A switched capacitor circuit samples two signals amplified by the preamplifier. Differential signals sampled by the switched capacitor circuit are respectively input to third and fourth input terminals of an integration circuit, and the integration circuit outputs differential signals obtained by those input signals to first and second output terminals. A second switching circuit switches a connection relationship between the switched capacitor circuit and the integration circuit. Each time the cycle changes, the first and second switching circuits switch the connection relationships to cause the signals amplified by the preamplifier to be sampled by double correlation sampling.