Sparse Pulsed Beam Depth Sensing for SPAD Spot Calibration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing depth mapping systems face challenges in accurately calibrating the locations of laser spots on single-photon avalanche diode (SPAD) arrays due to thermal and mechanical changes, leading to inefficiencies in power consumption and signal-to-background ratio, particularly in conditions of strong ambient light and long-range measurements.
Innovation Solution
A sparse emitter array with interleaved banks of emitters and a calibration method that pre-computes likely regions for laser spot imaging, using a two-stage approach to identify and verify spot locations, and synchronizes bank actuation to time-multiplex processing resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a dense array of emitters and sensing elements is used to improve measurement coverage, then the area covered increases, but power consumption and circuit complexity increase significantly
Solution Approach 1:
The emitter array is divided into multiple banks that are activated alternately in a time-multiplexed manner. This segmentation allows the system to cover the same area with fewer active emitters at any given time, reducing power consumption while maintaining full coverage capability through sequential activation of different banks.
2Measurement precision
If all sensing elements are actuated continuously to improve signal detection, then measurement accuracy improves, but power consumption and background noise increase
Solution Approach 1:
The sensing elements are actuated periodically in synchronization with the alternating emitter banks. Only the sensing elements corresponding to the currently active bank are enabled, creating a periodic activation pattern that reduces power consumption and background noise while maintaining measurement accuracy through coordinated time-multiplexed operation.
3Object-affected harmful factors
If the number of sensing elements exceeds the number of emitters, then signal-to-background ratio improves, but device complexity increases
Solution Approach 1:
The system transitions from a spatial mapping problem to a temporal solution by adding the time dimension through alternating bank activation. Multiple banks of emitters are activated sequentially in time, allowing more sensing elements to be effectively utilized without proportionally increasing emitter count, thereby improving signal-to-background ratio while managing complexity through time-multiplexing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances signal levels and accuracy of time-of-flight measurements by concentrating optical power in sparse spots, reducing circuit complexity and power consumption while maintaining high signal-to-background ratio, especially in challenging lighting conditions.
Implementation Method 1
The emitters in the array include vertical-cavity surface-emitting lasers (VCSELs)
Implementation Method 2
Objective optics are configured to form an image of the target scene on the array of sensing elements
Implementation Method 3
Some ToF systems use single-photon avalanche diodes (SPADs), also known as Geiger-mode avalanche photodiodes (GAPDs), in measuring photon arrival time
Implementation Method 4
measuring the round-trip time, i.e. time-of-flight (ToF), taken by the optical beams as they travel from the source to the target scene and back to a detector array
Data Source
Figure 1
Figure 2A
Figure 2B~2C
AI summary
Depth sensing apparatus (20) includes a radiation source (21), including a first array of emitters (54) arranged in multiple banks (52, 62), which are configured to emit a first plurality of pulsed beams (30) of optical radiation toward a target scene (32). A second plurality of sensing elements (78) are arranged in a second array (24) and are configured to output signals indicative of respective times of incidence of photons on the sensing elements, wherein the second plurality exceeds the first plurality. Objective optics (34) form an image of the target scene on the array of sensing elements. Processing and control circuitry (26, 28, 35) actuates the multiple banks in alternation and identifies, responsively to the output signals, areas of the second array on which the pulses of optical radiation reflected from corresponding regions of the target scene are incident.