Apparatus for measuring a distance between two running vehicles using

Abstract

To measure a distance between two running vehicles a measurement signal is first generated by irradiating a light beam toward an article to be measured and then receiving the reflected light beam from the article. A reference signal and the measurement signal generated in the above way are input to a digital mix-down circuit which comprises two-stage flip-flop circuit to determine a phase difference between the reference signal and the measurement signal. The apparatus includes a clock delay circuit for delaying the high-going (rising) edge of the measurement signal while the reference signal is going high at an output terminal of a flip-flop circuit on the input side of the digital mix-down circuit, and a data delay circuit for delaying the down-going (falling) edge of the reference signal input into a data terminal of the flip-flop circuit. Usually, the clock delay circuit is electrically connected to the digital mix-down circuit via the data delay circuit, while the data delay circuit is electrically connected directly to the digital mix-down circuit. Alternatively, both the clock delay circuit and the data delay circuit may be electrically connected directly to the digital mix-down circuit.