Patent ID: 6218982
Filing Date: 2001-04-17
Classification: G01S

Abstract:
A distance measurement apparatus comprising:pseudo-random-noise-code generating means for generating a pseudo random noise code in synchronism with a reference clock signal, the pseudo random noise code having a predetermined bit length;transmitting means for transmitting a first forward electromagnetic wave modulated in accordance with the pseudo random noise code generated by the pseudo-random-noise-code generating means;receiving means for receiving a first echo wave caused by reflection of the first forward electromagnetic wave at an object, and converting the received first echo wave into a binary signal;correlation calculating means for repetitively calculating a value of a correlation between the binary signal generated by the receiving means and the pseudo random noise code used for modulation of the first forward electromagnetic wave by the transmitting means at a predetermined period having a synchronous relation with the reference clock signal;first time measuring means for detecting a timing at which the correlation value calculated by the correlation calculating means peaks, and measuring a time interval taken by the first forward electromagnetic wave and the first echo wave to travel to and from the object in response to the detected timing;transmitted-pulse generating means for, after the time interval has been measured by the first time measuring means, outputting a transmitted pulse signal to the transmitting means and causing the transmitting means to transmit a second forward electromagnetic wave modulated in accordance with the transmitted pulse signal, wherein the receiving means is operative for receiving a second echo wave caused by reflection of the second forward electromagnetic wave at the object, and converting the received second echo wave into a received pulse signal;transmitted-pulse delaying means for delaying the transmitted pulse signal generated by the transmitted-pulse generating means by a delay time corresponding to the time interval measured by the first time measuring means, and thereby converting the transmitted pulse signal into a delayed transmitted pulse signal;second time measuring means for measuring a phase difference between the received pulse signal generated by the receiving means and the delayed transmitted pulse signal generated by the transmitted-pulse delaying means at a resolution higher than a resolution corresponding to the predetermined period of the correlation-value calculation by the correlation calculating means; anddistance calculating means for calculating a distance to the object on the basis of the time interval measured by the first time measuring means and the phase difference measured by the second time measuring means.