CPC H04R 3/00 (2013.01) [G01H 11/08 (2013.01); H03F 3/20 (2013.01); H03K 5/24 (2013.01); H03F 2200/03 (2013.01); H04R 2420/03 (2013.01)] | 17 Claims |
1. A method of determining a signal representative of the effect of external sound on a transducer being driven by an output signal from a switching amplifier having a zero voltage state, the transducer having a reactance that causes a current to continue to flow momentarily in the transducer when the output signal ceases, comprising the steps of:
disconnecting the transducer from the switching amplifier during an occurrence of the zero voltage state for a period of time shorter than a duration of the zero voltage state;
connecting a signal capture circuit around the transducer and measuring a current in the signal capture circuit during the period of time in which the transducer is disconnected from the switching amplifier, thereby capturing a signal caused by the inductance of the transducer, the captured signal containing both the output signal and the signal representative of external sound;
generating a modified captured signal containing the signal representative of external sound by removing a prediction of the output signal from the captured signal; and
wherein connecting the signal capture circuit around the transducer during the periods in which measurements are made comprises connecting a resistance around the transducer by means of a switch.
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