Circuitry and method for reducing echo walk error in a time-of-flight laser distance device

Abstract

A time-of-flight laser distance device includes a laser transmitter, a laser pulse return detector to receive reflected laser pulses, and comparators with respective first and second trip levels. A preliminary distance to a target is based on a linear ramp as a function of lapsed time from laser pulse generation through an effective time period wherein an associated return pulse is detected. Time-of-flight values associated with a leading edge of the return pulse are obtained at each of the first and second trip levels. A time difference is determined between the obtained values, and a correction factor is applied with respect to the preliminary measured distance based on the determined time difference. A dual ADC may be used wherein the leading edge of the return pulse is calculated by measuring a slope associated with the time-of-flight values and extrapolating a slope origin to a zero crossing point.