| 摘要 |
PROBLEM TO BE SOLVED: To decrease the number of external components when making an antenna input tuning circuit in IC which employs a digital tuning method. SOLUTION: The antenna input tuning circuit comprises a variable tuning filter 11 for varying tuning frequency f<SB>F</SB>by selecting a resistive element by switching, and an oscillation circuit 12 having the same configuration as the variable tuning filter 11. An oscillation frequency f<SB>L</SB>of the oscillation circuit 12 which is monitored with a frequency counter 13 is compared with a desired reception frequency f<SB>r</SB>which is preset by a control circuit 14, for their frequency count values. The oscillation frequency f<SB>L</SB>of the oscillation circuit 12 is changed so that both frequencies agree with each other within a tolerable error range, and the tuning frequency f<SB>F</SB>of the variable tuning filter 11 is also changed in accordance with it. So, without using a variable capacitance diode or the like which is difficult to be made in IC, the tuning frequency f<SB>F</SB>of the variable tuning filter 11 can be adjusted to agree with the desired reception frequency f<SB>r</SB>. COPYRIGHT: (C)2008,JPO&INPIT
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