| 摘要 |
PURPOSE:To simplify the detection/control system as well as the circuit constitution for a transmission fault by controlling the power supply voltage of the circuit at the first stage of a power amplifying part after detecting a faulty working of said power amplifying part and lowering the transmission output. CONSTITUTION:The power supply voltage of a power supply terminal 4 is supplied to the circuit at the first stage of a power amplifying part 2 via a transmission working detecting part 5 and a power supply control part 14. An operational amplifier 9 for comparison compares the power supply voltage with the voltage VN of a node 17. The voltage of a node 19 is higher than VN in a transmission unable mode. As a result, the output of the amplifier 9 is set at 0 and then delivered to a transmission working deciding part 11 as a transmission working unable detection signal. In the same way, the output of the amplifier 9 is set at 1 in a transmission working mode and delivered to the part 11 as a transmission working detection signal. Thus the circuit at the first stage of the part 2 is controlled by the parts 11 and 14, and the power supply voltage is kept at a normal level. In case a fault occurs in a transmission working mode and transmission start signal of a terminal 10 is turned off, the output of the part 11 is set at 0. Then the power supply voltage supplied to the part 2 is reduced down to a level divided by resistances 8 and 15. Thus the transmission output is lowered. |
