Low-Power Differential ToF Pixels for Dynamic Scene Detection
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Solution Overview
Problem
Time-of-flight (ToF) cameras are computationally and power-intensive, particularly when imaging static or slow-moving objects, as they continuously illuminate and process depth data at each pixel, leading to unnecessary power consumption.
Innovation Solution
Implement a scene-based operating mode that switches pixels between a lower power mode for static scenes and a higher power mode for dynamic scenes by using differential pixels, where charge accumulation is compared in the analog domain to determine brightness changes, thereby reducing the need for digital processing and memory storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ToF camera continuously illuminates and processes depth data at each pixel, then depth imaging capability is maintained, but power consumption increases unnecessarily for static scenes
Solution Approach 1:
The pixel array dynamically switches between two operational modes: a first mode for static scenes with reduced illumination and processing, and a second mode for dynamic scenes with full ToF processing. This dynamic adaptation allows the system to maintain depth imaging capability when needed while reducing power consumption during static periods.
Solution Approach 2:
The system changes operational parameters (illumination duty cycle, processing frequency, pixel activation state) based on scene activity detection. When static conditions are detected, parameters are adjusted to reduce power consumption while maintaining the ability to quickly transition back to full ToF operation when motion is detected.
2Measurement precision
If full ToF processing is performed at all pixels, then depth data accuracy is maintained, but computational resources and power are wasted on static regions
Solution Approach 1:
The pixel array is segmented into active regions requiring full ToF processing and inactive regions that can operate in a reduced mode. By dividing the scene into regions of interest (with motion) and non-interest regions (static), the system maintains depth accuracy where needed while eliminating computational waste in static areas.
Solution Approach 2:
Instead of applying full ToF processing uniformly across all pixels, the system applies partial processing only to regions where motion is detected. This partial action approach maintains measurement precision in dynamic regions while avoiding excessive computational resources in static regions.
3Use of energy by moving object
If pixel operates in lower power mode with selective clock activation, then power consumption is reduced, but processing speed may be affected
Solution Approach 1:
In the lower power mode, clock signals are activated periodically rather than continuously, with collection terminals selectively enabled for specific time intervals. This periodic activation reduces average power consumption while maintaining sufficient processing speed by concentrating computational effort into active periods and leveraging the ability to quickly transition to full-speed operation when motion is detected.
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
This approach significantly reduces power consumption by selectively illuminating and processing only dynamic regions of interest, maintaining frame rate requirements while optimizing power usage.
Implementation Method 1
A first photodetector of the differential pixel may accumulate a first amount of charge during a first time period based on incident photons
Data Source
Figure 1A~1C
Figure 2
Figure 3
AI summary
An imaging system includes a sensor array of differential pixels. A controller operates a first differential pixel of the sensor array in a first, lower power mode. The controller supplies a first clock signal to selectively activate a first collection terminal of the first differential pixel for a first duration, and a second clock signal to selectively activate a second collection terminal of the first differential pixel for a second duration. In an analog domain, a first amount of charge accumulated at the first collection terminal over the first duration is readout and compared to a readout of a second amount of charge accumulated at the second collection terminal over the second duration. Responsive to the first amount of charge being different from the second amount of charge by more than a threshold, the first differential pixel of the sensor array is operated in a second, higher power mode.