| 摘要 |
PROBLEM TO BE SOLVED: To prevent code errors from being generated even when the amplitude of a demodulation signal is changed by restoring the reference value to be a correct value in a short time, even when an erroneous value is set as the reference value so as to follow a small fluctuation in the demodulation signal. SOLUTION: When a received 4-value FSK signal is converted to a 4-value digital code, a mean value circuit 12 calculates a mean value of a demodulation signal 3, and the processing of increasing/decreasing overall the value of a digital signal is always conducted stepwise in a waveform shaping circuit 13, so that the mean value is a 2nd reference value. Thus, the effect of the fluctuations in the median of the demodulation signal 3 is reduced. A reference value generating circuit 14 revises the 1st and 3rd reference values, based on levels denoted by codes '10', '00' in the digital signal to reduce a code error caused by the effect of a change in the amplitude of the demodulation signal 3.
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