| 摘要 |
PURPOSE:To prevent the effect of secular change and temperature change due to the variance of modulation sensitivity and demodulation sensitivity by increasing the cut-off frequency of a high pass filter when it is discriminated that no low frequency component is included. CONSTITUTION:A discrimination means 10 is constituted to discriminate a pattern not to include a low frequency component with respect to a periodic pattern of 1010-and as the discrimination means 10, a coincidence detection means 11 detecting whether or not a bit is coincident with a preceding bit at each bit is used. Then the output x11 of the coincidence detection means 11 is given to a time constant means 12 applying slow charging at dissidence and slow discharge at coincidence, and the output of the time constant means 12 is compared with a prescribed value to obtain the result of discrimination. Then the output of the extraction means 9 is inputted to the discrimination means 10 and when it is judged that no low frequency component is included, the cut-off frequency of the high pass filter 1 is controlled to be increased.
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