| 摘要 |
PROBLEM TO BE SOLVED: To simplify the structure of terminal equipment in the case of making a speech between mutual terminal equipment. SOLUTION: A voice signal S111, inputted to terminal equipment T11, is amplitude-modulated by a voltage-current conversion circuit T121 and a current which coincides with a positive polarized PWM modulation signal S141, S142 supplied from a master set M1 to common lines L1, L2 and faces to diodes D11, D12, and the voltage current conversion circuit T121 is PAM-modulated and outputted. A current of the master set M1 is converted into a voltage by a current detection circuit M13, The voltage is sampled and held by an output of a clockϕ12 of a timing generator M11, and the polarity is inverted by a PWM generating circuit M12, where the signal is PWM-modulated in time division, to send out to the common line. The negatively polarized PWM modulation signal is inputted selectively by a terminal T12 so as to face to diodes D22, D21 and a speaker T132, and the voice signal S111 is sounded from the speaker T132. A voice signal S112 from the terminal T12 is reproduced by the terminal T11.
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