| 摘要 |
PURPOSE:To easily and accurately extract a Doppler signal by a simplified circuit, by efficiently taking out the Doppler signal using a sampling circuit, which makes an echo signal discrete at the cycle of a reference wave signal or at the cycle integral multiples of said cycle, as an echo signal demodulator. CONSTITUTION:The demodulation of an echo signal is performed by a sampling circuit. As the sampling circuit, two samplers 30a, 30b for converting the echo signal to a complex signal and a sample trigger generator 32 are provided. The sampler 30 takes in the output of a band-pass filter 15 in a discrete state and the timing making said output discrete is formed by the sample trigger generator 32. The discrete cycle of this case is set to one equal to the cycle of a reference wave signal or integral multiples of said cycle and, at the same time, the phases of discrete signals are shifted by pi/2 by the samplers 30a, 30b. By providing this pi/2 phase difference, the echo signal can be converted to the complex signal for obtaining the deflection of Doppler frequency and an sin trigger signal is supplied to the sampler 30a and a cos trigger signal is supplied to the sampler 30b.
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