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.

A radio frequency apparatus includes a power amplifier circuit, a signal coupling circuit, an extraction circuit, and a harmonic filter circuit. The power amplifier circuit is configured to amplify a differential signal to output a to-be-filtered signal. The signal coupling circuit includes a primary side inductor and a secondary side inductor. The signal coupling circuit is configured to convert the to-be-filtered signal received by the primary side inductor into a single-ended signal outputted from the secondary side inductor. The extraction circuit has a center tap. The extraction circuit is configured to inductively couple to the primary side inductor and output a common mode signal from the center tap. The harmonic filter circuit is configured to perform a harmonic filtering on the single-ended signal according to the common mode signal, such that the secondary side inductor of the signal coupling circuit outputs a filtered signal.

The present invention provides a single-end-to-differential microphone circuit and an electronic equipment, including: an amplifier, a microphone connected to the positive input end of the amplifier, a coupling capacitor C.sub.AC connected to the negative input end of the amplifier, a first feedback capacitor C.sub.FB1 connected to the negative output end of the amplifier, a first feedback resistor R.sub.FB1 connected in parallel with the first feedback capacitor C.sub.FB1, a second feedback capacitor connected to the positive output end of the amplifier C.sub.FB2, and a second feedback resistor R.sub.FB2 connected in parallel with the second feedback capacitor C.sub.FB1. The circuit of the present invention can adopt a microphone structure with smaller capacity, and at the same time has a better system signal to noise ratio.

A class D amplifier circuit receives an analog audio signal with a first reference voltage as its center level, and outputs an output pulse signal having a duty cycle that corresponds to the analog audio signal. A bias circuit generates a second reference voltage having a voltage level obtained as a division of the first reference voltage and the power supply voltage. A periodic voltage generating circuit of the class D amplifier circuit generates a periodic voltage having a triangle waveform or otherwise a sawtooth waveform having an amplitude that corresponds to the second reference voltage.

A current sense amplifier measures a voltage drop in a drive transistor LS to measure the current flowing through the drive transistor LS. The current sense amplifier includes a preamplifier pre-amp, to which a voltage across the drive transistor LS is inputted, and which obtains a positive output and a negative output corresponding to a voltage difference of the inputted voltage across the drive transistor; and a switch sw, which connects the input end of a common mode voltage vcm and the negative output, the common mode voltage vcm serving as the operation reference of the preamplifier pre-amp. A change of the positive output caused by turning on/off the switch sw can be detected.

A class-D amplifier includes a loop filter, a PWM generator coupled to the loop filter, a first multiplexer coupled to the PWM generator, a second multiplexer coupled to the PWM generator, and a power stage coupled to the first multiplexer and the second multiplexer. The loop filter is used to generate positive and negative LPF signals according to first and second analog signals, and first and a second feedback signals. The PWM generator is used to generate positive and negative PWM signals according to the positive and negative LPF signals respectively. The first and second multiplexer are used to output first and second MUX signals selected from a signal group. The power stage is used to generate a positive output signal to a positive output terminal according to the first MUX signal, and a negative output signal to a negative output terminal according to the second MUX signal.

A device includes a sensor signal input node and a high-pass filter stage. The high-pass filter stage includes an operational amplifier and a feedback integrator. The operational amplifier includes an input node coupled to the sensor signal input node. The feedback integrator is coupled between an output node of the operational amplifier and the input node of the operational amplifier to set a high-pass pole frequency of the high-pass filter stage.