| 摘要 |
PROBLEM TO BE SOLVED: To provide a transmitting-receiving circuit for information reading capable of protecting the receiving circuit against the excessive input by failure of a transmitting-receiving common antenna and the like. SOLUTION: In a range where a receiving line signal is smaller than a first level, based on a collation signal, a signal removal circuit outputs a collation signal leaking from a transmitting input part to a receiving output part and a removal signal of the amplitude reverse phase without saturation. In a range where a receiving line signal exceeds a second larger level than the first level, the above removal signal is constituted so as to be saturated. Further, as for the protection circuit, the level of a received signal is restricted or reduced in the range where the line signal exceeds a predetermined level the between the first level and the second level. COPYRIGHT: (C)2008,JPO&INPIT
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