| 摘要 |
PURPOSE:To obtain an optimum calling characteristic in response to the environment in operation by providing an automatic gain control amplifier circuit and a logarithmic amplifier circuit and switching both amplifier circuits selectively. CONSTITUTION:In the case of a personal call, a changeover switch 14 is switched to the position of a 1st contact 14a. Then the voice signal inputted via a microphone 11 is amplified by an AGC amplifier, and subjected to attenuation control by a calling attenuator 15 and fed to a hybrid circuit 16. Thus, even with noise therearound, the surrounding noise is suppressed to a low level by the action of the AGC amplifier circuit 12 and only the voice signal of the caller is sent with emphasis. Moreover, when the distance between the caller and the microphone 11 varies in the case of a conference talking, the changeover switch 14 is switched to the position of a 2nd contact 14b. The voice signal inputted via the microphone 11 is amplified, at this time, by the logarithmic amplifier circuit 13. Thus, both voice from a caller nearer the microphone 11 and that of a caller comparatively far from the microphone 11 are sent at a proper calling level.
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