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Radio frequency circuit for portable radion communication device

  • US 5,715,525 A
  • Filed: 06/26/1996
  • Issued: 02/03/1998
  • Est. Priority Date: 06/26/1995
  • Status: Expired due to Term
First Claim
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1. A radio frequency circuit for a portable radio communication device including a transmission terminal through which a transmission signal is introduced into the radio frequency circuit and a reception terminal through which a reception signal is output from the radio frequency circuit to another device, the radio frequency circuit comprising:

  • a first antenna capable of resonating at an FDD transmission frequency band used for transmission in a frequency division duplex system, resonating at an FDD reception frequency band used for reception in the frequency division duplex system, and resonating at a TDD system frequency band used in a time division duplex system, the TDD system frequency band differing from both the FDD transmission and reception frequency bands;

    a second antenna capable of resonating at the FDD reception frequency band;

    a first band-pass filter for permitting only components whose frequencies lie in the FDD reception frequency band to pass through with little attenuation, the first band-pass filter having an input terminal and an output terminal;

    a second band-pass filter for permitting only components whose frequencies lie in the FDD transmission frequency band to pass through with little attenuation, the second band-pass filter having an input terminal and an output terminal;

    a third band-pass filter for permitting only components whose frequencies lie in the TDD system frequency band to pass through with little attenuation, the third band-pass filter having first and second input/output terminals;

    first switching means for switching to connect either the first antenna or the second antenna with the input terminal of the first band-pass filter, and for switching to connect the first antenna with either the output terminal of the second band-pass filter or the first input/output terminal of the third band-pass filter;

    second switching means for switching to connect either the output terminal of the first band-pass filter or the second input/output terminal of the third band-pass filter with the reception terminal;

    third switching means for switching to connect either the input terminal of the second band-pass filter or the second input/output terminal of the third band-pass filter with the transmission terminal; and

    controlling means for controlling the first, second, and third switching means, the controlling means causing the second switching means to connect the reception terminal with the output terminal of the first band-pass filter, causing the third switching means to connect the transmission terminal with the input terminal of the second band-pass filter, and causing the first switching means to connect selectively either the first antenna or the second antenna with the input terminal of the first band-pass filter, thereby carrying out space diversity reception when selection of the frequency division duplex system is indicated, the controlling means causing the second switching means to connect the reception terminal with the second input/output terminal of the third band-pass filter, causing the third switching means to connect the transmission terminal with the second input/output terminal of the third band-pass filter, and causing the first switching means to connect the first antenna with the first input/output terminal of the third band-pass filter when selection of the time division duplex system is indicated.

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