| 摘要 |
PURPOSE:To eliminate mis-detection by detecting it that a DC component as a result of synchronous detection of a sinusoidal wave signal with the use of a phase synchronous circuit has a code change in a prescribed period so as to detect a sinusoidal wave signal received for a prescribed period. CONSTITUTION:An input signal is a signal of carrier frequency of the sampling series and a secondary cyclic filter 1 having a pole near the carrier frequency extracts the carrier frequency component. Let the input signal to a delay element 10 be e<j>T<(n)>. The DC component and the double frequency component of the carrier frequency are obtained by multiplying the rear part of the e<j>T<(n)>, Cos(theta0+omega)n with a Costheta'n of the output of the filter 1 by a multiplier 2 and only the DC component is obtained by a simple primary cyclic filter 3. Thus, the zero crossing of the signal is supervised for a predetermined prescribed period by a zero cross counter 4 and the carrier frequency component is detected by the absence of zero cross. Thus, mis-detection is not caused even with the signal level fluctuation or addition of noise in the transmission line.
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