| 摘要 |
<p>A portable telephone used in a first use mode where the telephone is in contact with the face and in a second use mode where the telephone is separated from the face. The portable telephone comprises a sensor (55) for measuring the distance from the face and an optical microphone comprising a diaphragm (2) vibrating with sound pressure, a light source (3) for irradiating the diaphragm (2) with a light beam, a photodetector (5) for receiving a fraction of the light beam reflected from the diaphragm (2) and outputting a signal corresponding to the vibration of the diaphragm (2), a circuit (13) for driving the light source (3) by supplying a specified current to the light source (3), and a circuit (100) for supplying a part of the output signal from the photodetector (5) to the light source driving circuit (13) as a negative feedback signal. The directivity of the optical microphone is controlled by varying the magnitude of the negative feedback signal with a sensor signal representing the separation distance.</p> |
