摘要 |
PROBLEM TO BE SOLVED: To provide a headset interface circuit which automatically switches the degree of amplification of a transmitter circuit or the bias current of a transmitter in accordance with the type of a headset. SOLUTION: In a headset interface circuit 17, the operation current of the transmitter of a headset 16 is detected by a current detection circuit 19; and when the headset 16 is found to be of an electret type as the result of this detection, a switch SWa of an amplification circuit 18 is switched to the side of an amplifier AMP1 having a low amplification factor, and a smaller bias current is selected. When it is of a carbon type, the switch SWa is switched to the side of an amplifier AMP2 having a high amplification factor, and a larger bias current is selected.
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