Multi-Purpose Time-to-Digital Converter for Depth Sensing
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Solution Overview
Problem
Depth sensing systems in artificial reality often have idle pixels during image frames, leading to inefficient use of sensor components and potential errors due to separate intensity and depth sensors being used in different locations.
Innovation Solution
A depth camera assembly with multi-purpose time-to-digital converters (TDCs) that allow pixels to perform TOF measurements, intensity measurements, and calibration within a single image frame, utilizing multiplexers to select between inputs and combine counters for increased dynamic range and reduced motion blur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If depth sensing systems use separate intensity and depth sensors located in different positions, then intensity measurement can be performed, but alignment errors occur between the two sensors
Solution Approach 1:
The patent combines intensity sensing and depth sensing functions into a single sensor array where each pixel can perform both TOF measurements and intensity measurements. This eliminates the alignment errors between separate sensors by using the same pixel location for both measurement types, while reducing device complexity by consolidating sensor functions.
Solution Approach 2:
The patent implements multi-functionality in each pixel by enabling it to perform multiple operations: TOF measurements for depth, intensity measurements for reflectivity, and calibration functions. This universal pixel design eliminates the need for separate dedicated sensors, resolving the contradiction between measurement precision and device complexity.
2Productivity
If pixels are used exclusively for TOF measurements during the entire image frame, then depth information can be continuously captured, but pixels remain idle during portions of the frame reducing efficiency
Solution Approach 1:
The patent implements periodic action by dividing the image frame into different time portions: some frames are dedicated to TOF measurements while other portions are used for intensity measurements and calibration. This periodic switching of pixel functions eliminates idle time and maximizes sensor utilization efficiency without compromising depth measurement capability.
Solution Approach 2:
The patent applies dynamics by making pixel functionality changeable over time - pixels dynamically switch between TOF measurement mode, intensity measurement mode, and calibration mode based on the current frame requirements. This dynamic reconfiguration eliminates wasted idle time while maintaining continuous depth sensing capability.
3Productivity
If intensity measurements are performed during TOF measurement portions of the frame, then sensor efficiency improves, but measurement precision decreases due to simultaneous operations
Solution Approach 1:
The patent applies segmentation by dividing the image frame into distinct time portions: TOF measurement portions and intensity measurement portions. By segmenting the temporal domain rather than spatial resources, the system achieves high sensor efficiency through multi-use of pixels while maintaining measurement precision through sequential rather than simultaneous operations.
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
Enables simultaneous capture of depth and intensity information, reducing errors from alignment issues and optimizing sensor usage by leveraging idle frame portions for additional functions, thereby enhancing the accuracy and efficiency of depth sensing.
Implementation Method 1
Each multi-purpose (TDC) comprises an oscillator and a counter
Implementation Method 2
One or more depth sensors detects reflected light from objects in the portion of the local area that include the light from the light projector
Data Source
AI summary
A depth camera assembly is used to obtain depth information describing a local area. The depth camera assembly includes a sensor having a plurality of pixels. Some or all of the pixels are divided into groups that are coupled to respective multi-purpose time-to-digital converters. Each multi-purpose time-to-digital converter comprises an oscillator and a counter. Each pixel in a group is associated with a multiplexer that is configured to select between inputs coupled to the pixel, the oscillator, or a counter associated with a different pixel. The multiplexer outputs the signal to the counter for the time-to-digital converter associated with the pixel. A time-of-flight measurement is taken during a first portion of an image frame. During a second portion of the image frame, the sensor may be used as an intensity counter. During a third portion of the image frame, the depth sensor may be calibrated.