| 摘要 |
PURPOSE:To miniaturize a telephone set by designing a microphone amplifier and a speaker amplifier as a microphone amplifier and a speaker amplifier with a gain control function changing the gain depending on loudspeaking and handset talking. CONSTITUTION:A handset talking detection switch 15 controls a gain control circuit 16 at handset talking to lower the gain of the microphone amplifier 2 and the speaker amplifier 4. Further, inhibit circuits 23, 24 inhibit loss addition function of loss addition analog switches 21, 22 to use a talking circuit 20 at handset talking state. Since a switch 15 is turned off at loudspeaker talking and stand-by state, the gain of the amplifiers 2, 4 is switched to a high gain and the circuit 20 is in the loudspeaking state. In this case, when a loudspeaker switch 12 is turned on, a line L1/L2 is connected to the circuit 20 via the switch 12 to attain talking with the loudspeaking state. Thus, both the talking sections are used in common and the telephone set is miniaturized. |
