| 摘要 |
A transmitting/receiving circuit for a mobile radio communication system includes an antenna 2, for transmitting and receiving a radio wave, to which first and second variable band-pass filters 30, 32 are connected. First filter 30 is used for an input stage of a receiving circuit and second filter 32 is used for an output stage of a transmitting circuit. The receiving and transmitting circuits are provided with PLL synthesizers 8 and 14 respectively. Each filter includes variable capacitance diodes. The variable capacitance diodes of the first filter are controlled by a control voltage from the PLL synthesizer 8 and the variable capacitance diodes of the second filter are controlled by a control voltage from the PLL synthesizer 14. in a second embodiment only one synthesizer is used. <IMAGE>
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