TEMPORAL JITTER IN A LIDAR SYSTEM
A LIDAR system having light emitters and light detectors can apply per-shot jitter to create variation in the interval between successive emitter pulses. Operation of the detectors can be synchronized with operation of the emitters so that a consistent time of flight measurement corresponds to a consistent distance. Application of per-shot jitter can reduce the effect of crosstalk from other sources of pulsed light and can also reduce range aliasing effects.
1 . A LIDAR system comprising:
a light transmission module having an emitter to emit a light pulse during each of a plurality of shots in response to a trigger pulse;
a light sensing module having at least one light sensor channel to receive light and configured to generate, responsive to the trigger pulse, a histogram of received light intensity as a function of time for a sequence of time bins, the light sensing module further having a first memory circuit configured to accumulate the histogram across the plurality of shots; and
a timing controller coupled to the light transmission module and the light sensing module and configured to generate a sequence of trigger pulses to synchronize operation of the light transmission module and the light sensing module for each shot,
the timing controller being further configured to apply a per-shot jitter to each trigger pulse, wherein the per-shot jitter varies for different shots, and wherein, for at least some of the shots in the plurality of shots, the per-shot jitter is greater than one time bin.
2 . The LIDAR system of claim 1 wherein the per-shot jitter is selected within a predefined range of jitter values using an equal-energy sampling technique.
3 . The LIDAR system of claim 2 wherein the predefined range of jitter values is from zero to 20% of a total number of time bins in the histogram.
4 . The LIDAR system of claim 2 wherein the predefined range of jitter values is from zero to 120% of a total number of time bins in the histogram.
5 . The LIDAR system of claim 1 further comprising:
a second memory circuit configured to store a master jitter sequence containing a sequence of jitter values uniformly distributed over a range of jitter values,
wherein the timing controller is further configured to select the per-shot jitter for each trigger pulse according to the master jitter sequence.
6 . The LIDAR system of claim 5 further comprising:
control logic to randomly select a starting position in the master jitter sequence during a system startup operation.
7 . The LIDAR system of claim 1 further comprising:
a processor configured to analyze the histogram to determine whether crosstalk is present.
8 . The LIDAR system of claim 7 wherein the processor is further configured to adaptively modify the per-shot jitter in response to determining that crosstalk is present.
9 . The LIDAR system of claim 1 wherein the emitter emits a light pulse train consisting of one or more light pulses during each shot, the light pulses of the light pulse train having a fixed temporal relationship to each other.
10 . The LIDAR system of claim 1 wherein:
the light transmission module includes a plurality of emitters;
the light sensing module includes a plurality of light sensor channels; and
the timing controller is configured such that the same per-shot jitter is applied to each of the plurality of emitters and to each of the plurality of light sensor channels.
11 . A method of operating a LIDAR system, the method comprising:
capturing a plurality of shots, wherein capturing each shot in the plurality of shots includes:
determining a per-shot jitter;
generating, in a timing controller of the LIDAR system, a trigger pulse at a time determined based at least in part on the per-shot jitter;
operating a light-transmission module of the LIDAR system to emit a light pulse synchronized with the trigger pulse; and
operating a light-sensing module of the LIDAR system synchronously with the trigger pulse to receive light and to accumulate a histogram of received light intensity as a function of time, the histogram defining a series of time bins, wherein the histogram is accumulated across the plurality of shots and wherein, for at least some of the shots in the plurality of shots, the per-shot jitter is greater than one time bin; and
subsequently to capturing the plurality of shots, computing ranging information based at least in part on the histogram.
12 . The method of claim 11 wherein determining the per-shot jitter for each shot includes selecting the per-shot jitter within a predefined range of jitter values using an equal-energy sampling technique.
13 . The method of claim 12 wherein the predefined range of jitter values is from zero to 20% of a total number of time bins in the histogram.
14 . The method of claim 12 wherein the predefined range of jitter values is from zero to 120% of a total number of time bins in the histogram.
15 . The method of claim 11 wherein determining the per-shot jitter for each shot includes accessing successive locations in a master jitter sequence stored in a memory of the LIDAR system.
16 . The method of claim 15 wherein determining the per-shot jitter for each shot includes randomly selecting a starting position in the master jitter sequence.
17 . The method of claim 11 further comprising:
analyzing the histogram to determine whether crosstalk is present.
18 . The method of claim 17 further comprising:
adaptively modifying the per-shot jitter in response to determining that crosstalk is present.
19 . The method of claim 11 wherein operating the light-transmission module of the LIDAR system includes operating a single emitter to emit a light pulse train consisting of one or more light pulses during each shot, the light pulses of the light pulse train having a fixed temporal relationship to each other.