| 摘要 |
PROBLEM TO BE SOLVED: To provide a security tag capable of uniformizing its reception sensitivity uniform thereby improving its quality by adjusting reception sensitivity to a radio wave by adjusting the bias voltage of a transistor with a 2nd external output signal which is inputted through an antenna. SOLUTION: An input circuit 81 inputs external output signals from an antenna or gate and a resetter by a radio wave detection part 83. A signal inputted through the radio wave detection part 83 is inputted to a signal amplification part 97 through an input protection part 91. A coupling capacitor 127 is put between the signal amplification part 97 and a waveform shaping part 115 to cut the DC component of a signal inputted to a 2nd-stage transistor 117 of the waveform shaping part 115. Consequently, the best bias voltage determined by resistances 119 and 121 can be set irrelevantly to the DC component of the signal amplified by a 1st-stage transistor 99. Consequently, the amplification factor can drastically be improved.
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