Tapped delay line high speed register

Abstract

A clockless time-of-flight interval timer includes a tapped delay line register comprising N buffers that each contribute a substantially identical incremental time delay. A latched version of a START pulse associated with an output of transmitted energy from a laser is propagated through the tapped delay line. A DATA signal representing a detected pulse returned from a target is coupled to a block of four comparators each having a different signal threshold. The output of each comparator block is provided as input to one of four channel registers, each register comprising N D-type flipflops separately but synchronously triggerable by tapped incrementally delayed outputs from the N buffers. Channel register outputs are multiplexed and decoded and interfaced with a microprocessor. The microprocessor determines first signal time over threshold (FOT) information and total time over threshold (TOT) information from the channel registers. The FOT provides a measure of time-of-flight, which measure can be corrected using TOT information and a look-up table containing timing walk incremental delay corrections for individual ones of the N buffers. TOT information can be used as an indicator of signal strength and thus may be used to correct for systematic errors in measured delay, which arise from fluctuation in signal strength.