Automatic and dynamic noise cancellation for microphone-speaker combinations

An audio host device comprising:

• a headset connector having a speaker contact, a microphone contact, and a reference contact, the reference contact to be shared by a microphone and a speaker of a headset that is to be coupled to the connector, the reference contact being directly coupled to a power return plane of the audio host device;
• a programmable gain amplifier, PGA, having a signal input coupled to a sense point for the reference contact;
• a first difference amplifier having a pair of inputs, one of the pair of inputs being coupled to the microphone contact, and the other being coupled to a signal output of the PGA through a first gain stage;
• a second difference amplifier having a pair of inputs, one of the pair of inputs being coupled to the microphone contact, and the other being coupled to the output of the PGA through a second gain stage having a different gain than the first gain stage;
• a third difference amplifier having a pair of inputs, one of the pair of inputs being coupled to the microphone contact, and the other being coupled to the output of the PGA through a third gain stage having a gain in between that of the first and second gain stages;
• and
• a controller having an output coupled to a control input of the PGA.

A method for operating an audio host device having a headset electrical interface, comprising:

• a) sensing a reference contact of the headset electrical interface according to a gain setting, wherein the reference is shared by a speaker and a microphone of a microphone-speaker combination that are coupled to the headset electrical interface;
• b) generating a first voltage difference between a microphone contact of the interface and the sensed reference contact amplified according to a first gain value;
• c) generating a second voltage difference between the microphone contact and the sensed reference contact amplified according to a second, different gain value;
• d) generating a third voltage difference between the microphone contact and the sensed reference contact amplified according to a third gain value that is in between the first and second gain values;
• e) monitoring each of the first and second voltage differences;
• and
• f) changing the gain setting for sensing the reference contact.