Audio amplifier offset reduction using digital input/output comparisons

A method of reducing DC offset in an analog output of an electronic audio device that receives digital input values from which an output signal provided by the analog output is generated, the method comprising:

• monitoring the output signal for events having a time related to the DC offset;
• comparing first transitions resulting from the monitoring to second transitions in the digital input values, wherein the comparing determines the value of the DC offset during a measurement intervals;
• generating, from a result of the comparing, a correction value for the output signal that removes the DC offset;
• triggering the measurement intervals at periods of greater than 50 milliseconds;
• correcting the output signal according to the correction value;
• and
• holding the correction value between the measurement intervals, whereby continuous changes in the DC offset caused by the correcting are avoided.

An electronic audio device, comprising:

• an audio output for providing an audio output signal to an external device, wherein the audio output signal has a DC offset;
• a digital-to-analog converter for converting digital input values to an analog signal at an output of the digital-to-analog converter, wherein the audio output is generated from the output of the digital-to-analog converter;
• an audio output monitor having an input coupled to the audio output signal, wherein the audio output monitor is a zero-crossing detector implemented by a chopped comparator;
• a pseudo-random sequence generator for generating a chopping control signal, wherein a control input of the chopped comparator is coupled to an output of the pseudo-random sequence generator;
• a comparison circuit for comparing an output of the audio output monitor with the digital input values to generate error values indicative of a DC offset of the audio output signal from a comparison of first transitions in the output of the audio output monitor with second transitions in the digital input values;
• a combining circuit for adjusting the digital input values in conformity with the error values to reduce the DC offset of the audio output signal.

An electronic audio device, comprising:

• an audio output for providing an audio output signal to an external device, wherein the audio output signal has a DC offset;
• a digital-to-analog converter for converting digital input values to an analog signal at an output of the digital-to-analog converter, wherein the audio output is generated from the output of the digital-to-analog converter;
• an audio output monitor having an input coupled to the audio output signal, wherein the audio output monitor is a zero-crossing detector implemented by a chopped comparator, wherein the chopped comparator comprises an offset removal circuit including an integrator for integrating an unrestored output of the chopped comparator and an input offset adjusting circuit responsive to an output of the integrator;
• a comparison circuit for comparing an output of the audio output monitor with the digital input values to generate error values indicative of a DC offset of the audio output signal from a comparison of first transitions in the output of the audio output monitor with second transitions in the digital input values;
• and
• a combining circuit for adjusting the digital input values in conformity with the error values to reduce the DC offset of the audio output signal.

An electronic audio device, comprising:

• an audio output for providing an audio output signal to an external device, wherein the audio output signal has a DC offset;
• a digital-to-analog converter for converting digital input values to an analog signal at an output of the digital-to-analog converter, wherein the audio output is generated from the output of the digital-to-analog converter;
• an audio output monitor having an input coupled to the audio output signal;
• a comparison circuit for comparing an output of the audio output monitor with the digital input values to generate error values indicative of a DC offset of the audio output signal from a comparison of first transitions in the output of the audio output monitor with second transitions in the digital input values, wherein the comparison circuit includes a hold function, wherein the comparison circuit determines the value of the DC offset during a measurement interval and holds the output of the comparison circuit after the measurement interval, whereby continuous changes in the DC offset caused by changes in the output of the comparison circuit are avoided, wherein the measurement interval is triggered by changes in a control value of a volume control coupled between the output of the digital-to-analog converter and the audio output;
• and
• a combining circuit for adjusting the digital input values in conformity with the error values to reduce the DC offset of the audio output signal.

A method of reducing DC offset in an analog output of an electronic audio device that receives digital input values from which an output signal provided by the analog output is generated, the method comprising:

• monitoring the output signal for events having a time related to the DC offset;
• comparing first transitions resulting from the monitoring to second transitions in the digital input values, wherein the comparing determines the value of the DC offset during a measurement intervals;
• generating, from a result of the comparing, a correction value for the output signal that removes the DC offset;
• triggering the measurement intervals in response to changes in a control value of a volume control coupled to the digital input values and the analog output;
• correcting the output signal according to the correction value;
• and
• holding the correction value between the measurement intervals, whereby continuous changes in the DC offset caused by the correcting are avoided.