| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a multi-band type portable telephone set of which the safety is increased, by preventing heating of power amplifiers, when a fault occurs in negative bias voltages of the power amplifiers or in a drive circuit. <P>SOLUTION: The multi-band type portable telephone set is provided with power amplifiers 31, 32 corresponding to a plurality of bands to be used; a negative voltage generating circuit 33 for supplying a negative bias voltage to each of the power amplifiers; P-channel FETs 34, 35 connected between the power amplifiers and a power source and normally controlled to OFF by being pulled-up by their inputs, up to the power source via resistors 36, 37; and N-channel FETs 38, 39 which are turned on by band signals 21, 22, corresponding to the plurality of bands to be used, to control the corresponding P-channel FETs 34, 36 to be turned on. The multi-band portable telephone set is further provided with N-channel JFETs 44, 45 which are connected between the N-channel FETs and a ground and turned on, when the negative bias voltage is not generated from the negative voltage generation circuit to control the N-channel FETs 38, 39 to be turned off. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
