PURPOSE: To reduce erroneous code discrimination regardless of the change of the center voltage of a detection signal due to the variance of the transmission frequency, the temperature change of a receiver, the variance of the supply voltage, or the like ;CONSTITUTION: An averaging circuit 104 obtains an average value of the detection signal, and a waveform shaping circuit 105 shapes the detection signal by this average value, and a synchronizing part 106 outputs a timing signal synchronized with the shaped detection signal. An input switching part 107 and a digital signal conversion part 108 convert the average value of a detection signal at the time of detection of a preamble signal and the detection signal at the other time into digital signals based on the timing signal and the preamble detection signal of a preamble detection part 109, and a code discriminating part 110 discriminates the code by the digital signal processing with the average value of the detection signal as the reference level.;COPYRIGHT: (C)1995,JPO
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