Addressable VCSEL Dot Projector for Faster ToF Depth Readout
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional depth cameras face challenges in increasing readout speed from direct time of flight sensors and reducing the impact of background light, leading to low-quality depth reconstruction and inefficient power consumption.
Innovation Solution
A depth camera assembly (DCA) with an addressable illumination source and a detector system that includes charge-based memory elements, row and column decoders, and an analog-to-digital converter, allowing for efficient data capture and processing of photon detection events using a timing reference and addressing logic to activate individual emitters, thereby improving depth resolution and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional depth cameras use direct time of flight sensors, then depth sensing capability is achieved, but readout speed is slow and background light interference is high
Solution Approach 1:
The detector is divided into multiple independently readable regions or blocks, allowing parallel readout operations. This segmentation enables different portions of the detector to be read simultaneously through multiple output channels, significantly increasing the overall readout speed without compromising the measurement precision of individual pixels.
Solution Approach 2:
Charge-based memory elements are introduced as intermediary components between the photodetectors and the readout circuitry. These memory elements temporarily store the charge signals from multiple pixels, allowing the readout system to process and transfer data at higher speeds without losing signal integrity or depth measurement accuracy.
2Measurement precision
If conventional depth cameras operate in environments with background light, then continuous operation is possible, but background light degrades depth sensing accuracy
Solution Approach 1:
The system employs periodic modulation of the illumination source at specific frequencies, and the detector is synchronized to detect only at these modulated frequencies. This periodic action allows the system to distinguish between the modulated illumination signal and ambient background light, maintaining depth sensing accuracy even in environments with continuous background illumination.
Solution Approach 2:
The system utilizes wavelength-specific detection by tuning the photodetectors to respond to the specific wavelength of the illumination source. This wavelength selectivity acts as an optical filter, allowing the detector to ignore background light at different wavelengths and maintain measurement precision by detecting only the reflected illumination signal.
3Measurement precision
If addressable illumination blocks are used to improve depth mapping accuracy, then depth resolution increases, but device complexity increases
Solution Approach 1:
The illumination source is divided into multiple addressable blocks or regions that can be independently controlled and activated. This segmentation allows the system to illuminate only specific regions of interest at any given time, improving depth mapping accuracy for targeted areas while managing overall system complexity through modular control architecture.
Solution Approach 2:
The system dynamically activates specific illumination blocks based on the current field of view and depth sensing requirements. Rather than illuminating all blocks simultaneously, the control system dynamically selects and activates only the necessary blocks, improving measurement precision where needed while reducing unnecessary complexity and power consumption in inactive regions.
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
The DCA enhances depth mapping accuracy and reduces power consumption by enabling high-fidelity sparse depth sensing and efficient data processing, facilitating immersive virtual and augmented reality applications.
Implementation Method 1
The row decoder may comprise a voltage controlled oscillator
Implementation Method 2
Each pixel may comprise a charge based memory element configured to store information describing a number of photons detected by the pixel
Implementation Method 3
The output bus may be coupled to an analog to digital converter including a lookup table configured to correct non-linearity in the fixed charge transfer function
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A direct time of flight depth system (340) includes an addressable illumination source (350), an active depth sensor (355), and a controller (360). The addressable illumination source (350) includes an array of emitters (e.g., vertical-cavity-surface-emitting lasers, VCSELs) and an optical assembly that is used to generate an array of dots emitted into a local area (345). Each emitter is independently addressable, allowing selective illumination of different portions of the local area (345). The addressable illumination source (350) is aligned with the active depth sensor (355) so each dot maps to a corresponding macropixel (e.g., 4 x 4 array of SPADs) on the active depth sensor (355). Data from the active depth sensor (355) is read out and used to determine depth information.