Techniques for mute pattern injection for a pulse-density modulation microphone are described. In one or more implementations, a pulse-density modulation (PDM) microphone includes a transducer that receives a pressure wave and produces an analog signal that represents the pressure wave, an analog-to-digital converter (ADC) that receives the analog signal from the transducer and converts the analog signal into a digital PDM signal. The PDM microphone also includes a pattern generator that generates a digital mute signal, a controller that outputs control signals, and a multiplexer that receives the control signals, the digital mute signal, and the digital PDM signal. The multiplexer transmits the digital mute signal or the digital PDM signal, responsive to the control signals.

A power amplifier device includes first and second pairs of semiconductor switches, transformers, and a zero-crossing detection circuit for detecting a zero voltage crossing of an analog input signal. The switches of the first pair receive a respective positive and negative component of the input signal. The transformers store energy from the positive and negative components, respectively. Each transformer releases accumulated energy when the respective switch of the first pair turns off The switches of the second pair have opposite switching states and are connected between a respective transformer and a load, e.g., a transducer, speak, or motor. Each switch receives released energy from the respective transformer. A switching state of each switch of the second pair changes in response to a detected zero voltage crossing of the input signal to transfer the released energy to the load. A system includes the device and the load.

The present disclosure discloses an audio processing apparatus having noise reducing mechanism. A DSP circuit generates N-bit digital audio signal, N being an integer larger than 1. A first modulation circuit truncates the digital audio signal and performs a first modulation processing based on pulse width or pulse density modulation to generate a single-bit waveform modulated signal. An amplifier includes a single-bit DAC circuit, a second modulation circuit and a driving circuit. The single-bit DAC circuit converts the single-bit waveform modulated signal to generate an input analog signal. The second modulation circuit subtracts the input analog signal and an output modulated signal to generate a subtraction result and performs a second modulation processing thereon to generate a control signal. The driving circuit generates the output modulation signal according to the control signal and transmits the output modulation signal to the second modulation circuit through a closed-loop feedback path.

Techniques for mute pattern injection for a pulse-density modulation microphone are described. In one or more implementations, a pulse-density modulation (PDM) microphone includes a transducer that receives a pressure wave and produces an analog signal that represents the pressure wave, an analog-to-digital converter (ADC) that receives the analog signal from the transducer and converts the analog signal into a digital PDM signal. The PDM microphone also includes a pattern generator that generates a digital mute signal, a controller that outputs control signals, and a multiplexer that receives the control signals, the digital mute signal, and the digital PDM signal. The multiplexer transmits the digital mute signal or the digital PDM signal, responsive to the control signals.

An amplifier may include a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal which is a function of the intermediate signal at an amplifier output, and a signal feedback network coupled between the amplifier output and input. The final output stage may be switchable among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal. Structure of the feedback network and the first stage may remain static when switching between modes.

A pulse modulator receives an analog voltage V.sub.IN, and generates a pulse signal that is modulated according to the analog voltage V.sub.IN. An output stage generates a switching signal at an output terminal according to the pulse signal. A semiconductor integrated circuit is switchable between (i) a normal mode in which a main signal V.sub.MAIN to be used in a normal operating mode is input as the analog voltage V.sub.IN to the pulse modulator, and (ii) a test mode in which at least one internal analog signal V.sub.AUX generated in the semiconductor integrated circuit is input as the analog voltage V.sub.IN to the pulse modulator.

The present invention discloses an audio processing circuit, wherein when the audio processing circuit determines that a signal being processed is a small signal, an output stage uses a regulated supply voltage provided by a voltage regulator, and the output stage uses an open-loop structure to reduce noise of an output audio signal; and when the audio processing circuit determines that the signal being processed is a large signal, the output stage directly uses the supply voltage without using the regulated supply voltage, and the output stage uses a closed-loop structure to reduce the total harmonic distortion of the output audio signal. By using the present invention, the audio processing circuit can have a good performance indicator with a small chip area design.

An amplifier may include a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal which is a function of the intermediate signal at an amplifier output, and a signal feedback network coupled between the amplifier output and input. The final output stage may be switchable among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal. Structure of the feedback network and the first stage may remain static when switching between modes.

An amplifier may include a first stage configured to receive an input signal at an amplifier input and generate an intermediate signal which is a function of the input signal, and a final output stage configured to generate an output signal which is a function of the intermediate signal at an amplifier output, and a signal feedback network coupled between the amplifier output and input. The final output stage may be switchable among a plurality of modes including at least a first mode in which the final output stage generates the output signal as a modulated output signal which is a function of the intermediate signal, and a second mode in which the final output stage generates the output signal as an unmodulated output signal which is a function of the intermediate signal. Structure of the feedback network and the first stage may remain static when switching between modes.

Circuit topologies and control methods for a dc-to-rf converter circuit are described.