Nxp B.v.

Koninklijke Philips Corporation N.v.

Goodix Technology (Hk) Company Limited

Han Martijn Schuurmans

Maarten Van Dommelen

Marco Berkhout

Lûtsen Ludgerus Albertus Hendrikus Dooper

Maarten Wilhelmus Henricus Marie Van Dommelen

An audio amplifier system is described comprising: a variable gain audio processor for processing digital audio signal, a digital to analog converter coupled to the audio processor, and configured to receive the processed digital audio signal, a variable gain amplifier having an input coupled to the output of the digital to analog converter and operably connected to a power supply, a controller coupled to the variable gain audio processor and the variable gain amplifier and configured to switch the audio amplifier system between a first operating mode having a first power supply voltage value and a second operating mode having a second higher power supply voltage value; wherein the controller is operable in the first operating mode to set the audio amplifier system gain to a desired gain value and in the second operating mode to maintain the desired gain value.

Audio amplifier system

A microphone circuit has a clip detection circuit () which detects when an analog to digital converter (ADC,) output has reached a threshold. A variable capacitance (), which functions as a variable input load associated with the microphone (), is controlled based on the clip detection circuit output, the feedback is thus based on the ADC output level, and the processing of this signal can be implemented without requiring baseband processing of the signal&#x2014;it can simply be based on a state of the ADC output.

Control of a microphone

A microphone circuit has a clip detection circuit which detects when an analogue to digital converter output has reached a threshold. A variable attenuator is controlled based on the clip detection circuit output. The feedback is thus based on the ADC output level, and the processing of this signal can be implemented without requiring baseband processing of the signal&#x2014;it can simply be based on a state of the ADC output. An overrule function is also provided so that the clip detection AGC control can be inhibited or controlled differently.

A true ground amplifier circuit in which a voltage sensor senses the output voltage and generates a binary output which indicates whether the output is above or below a threshold. A variable gain feedback system generates a feedback signal for combination with the digital input, thereby to provide offset cancellation. The variable gain is reduced over time to provide offset cancellation during an initial period of time of operation of the amplifier circuit. This provides offset cancellation during a start-up period, for example.

Amplifier circuit and amplification method

An analog to digital converter comprises an input terminal configured to receive an analog input signal and an output terminal configured to provide an output digital signal. The analog to digital converter also comprises a main summer having a summing input, a subtracting input and a summing output, wherein the summing input is connected to the input terminal; an analog filter having a filter input and a filter output, wherein the filter input is connected to the summing output; a quantizer having a quantizer input and a quantizer output, wherein the quantizer input is connected to the filter output; a digital integrator having a digital integrator input and a digital integrator output, wherein the digital integrator output is configured to provide a multi-bit output signal, the digital integrator input is connected to the quantizer output, and the digital integrator output is connected to the output terminal; and a main feedback digital to analog converter having a main feedback converter input and a main feedback converter output, wherein the main feedback converter input is connected to the digital integrator output, and the main feedback converter output is connected to the subtracting input of the main summer.

Analogue to digital converter

An amplifier is disclosed, wherein the output stage is split between a primary output stage and a secondary stage. To minimize or eliminate any audible plop when the amplifier is switched on, the primary stage is connected, and the second stage is gradually connected using a switch. The gradual connection can be by means of varying the pulse-density of a pulse wave modulation on the switch, from fully open (0% pulse-density) to fully closed (100%). The inverse process can minimize or eliminate plop during switch-off. Separate feedback loops are switchable, from the primary and secondary stages; in a DC-coupled embodiment, the feedback loop from the secondary stage may include DC-offset cancelling circuitry, to both reduce or eliminate the plop and avoid and DC-offset current through the speaker.

Plop-free amplifier

A class H amplifier circuit includes a Buck converterand a charge pumpwhich are used to generate voltages which are used in turn to power an output driver. A feedback pathcontrols the loop. The circuit is particularly suitable as a high efficiency circuit for driving headphones or loudspeakers.

Class H amplifier

The invention relates to a Sigma Delta A/D converter () for generating a N-bits digital output signal () on the basis of an analogue input signal (), comprising a control loop which comprises a quantizer () comprising at least a comparator () for generating the N-bits digital output signal () and a D/A converter () in a first feedback loop () of the control loop for generating an analogue version () of the N-bits digital output signal () on the basis of the N-bits digital output signal (), wherein the quantizer () also comprises an Up-Down counter () which is coupled to the comparator (), wherein the D/A converter () is coupled to the comparator () in a second feedback loop () of the control loop.

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Cuijk, Netherlands

Han Martijn Schuurmans