| 摘要 |
PURPOSE:To prevent a leak of carrier wave signal when data is not transmitted by supplying one terminal of the input to which a signal voltage from a differential amplifier circuit is to be inputted with a voltage equal to the fixed voltage for the other input terminal during the time when data transmission is not executed. CONSTITUTION:During a time when data is not transmitted, a cut-off signal is in H-level, and a voltage 2.3-2.4V which is approximately equal to the fixed voltage V1 supplied to one input terminal is impressed to the other input terminal of the differential amplifier circuit 17 of a transformer 5 from abias setting circuit 20. Accordingly, the circuit 17 operates amplifier circuits 15, 16 in a status to give approximately same gains. Therefore, carrier wave signals in equal levels having a phase difference of 180 degrees are outputted from the circuits 15, 16, which offset each other not to be outputted. The modulator 5 at this time is in the operating status oscillating carrier wave signals, and is able to transmit data upon receiving a transmission request signal. At the time of transmitting a data, the circuit 20 does not operate, and a modulated wave is outputted from the modulator 5 in response to a binary signal supplied from a level adjusting circuit 4.
|
