On the minimization of timing walk in industrial pulsed time-of-flight laser radars

摘要

Pulsed time-of-flight laser ranging is based on measuring the transit time of a short laser pulse to an optically visible target and back to the receiver. These techniques are gaining in popularity for industrial distance measurement applications. The laser pulse length typically used is in the range of 3 ns, which corresponds to about 1 m in air. This pulse length poses a challenge for detection of the echo from the target since the accuracy aimed at in a single shot is typically at the level of a few centimetres or even better with a dynamic range of more than 1:10 000. This paper studies the possibility of realizing the timing detection of the laser pulses with a straight-forward leading edge type of receiver that detects the cross-over of the received pulse with respect to a set reference level. Without any other measures the timing walk error that would be produced with this kind of receiver, would be at the level of nanoseconds. However, by measuring either the width or the slew rate of the rising edge of the received pulse, timing walk can be compensated for based on the measured dependence of the walk on the respective parameter. The advantage of these methods is that they are effective even when the optoelectronic receiver is saturated, thus enabling one to achieve wide dynamic operating range. Using these time-domain walk compensation methods we have constructed fully integrated CMOS and BiCMOS laser radar receivers that achieve timing walk error of less than +/-30ps in dynamic range of 1:10 000 -100 000.