| 摘要 |
PROBLEM TO BE SOLVED: To provide a timing circuit with high-accuracy such that time resolution is independent of a clock rate of an oscillator. SOLUTION: A counting operation in a counter 8 is stopped by a receiving timing pulse which is output from a receiving timing detecting circuit 10. In addition, when the receiving timing pulse is output, received signals are sampled by a clock pulse which is generated by a received wave sampling circuit 11 and the sampled signals is converted to digital data by an A/D converter 12. The digital data are sent to a microcomputer 9 where a zero-cross-point Pc of the received signal is determined by interpolation process. An elapsed-time T0 between transmitting and receiving of ultrasonic is calculated, based on an elapsed-time (Δt+tc ) between the zero-cross point Pc of the received wave signal which is determined through the interpolation process and a receiving timing pulse position, end an elapsed-time Ta determined by a counter.
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