Global Shutter Pixel Circuit for Low-Power ToF Calibration
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Solution Overview
Problem
Conventional CMOS pixel sensors for time-of-flight (ToF) depth measurement systems face challenges such as large size and high power consumption, which are undesirable for mobile computer vision applications.
Innovation Solution
A ToF imaging system with a pixel array that includes an active region for depth measurement and a feedback region for calibration, utilizing optical feedback and fast image processing to achieve high accuracy depth measurements with minimal impact on sensor performance and power consumption. The system employs a small feedback region for quick sensing and signal processing, and optical fiber for strong feedback illumination, allowing for run-time calibration without affecting frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CMOS pixel sensors are used for ToF depth measurement, then depth measurement capability is achieved, but device size and power consumption increase
Solution Approach 1:
The pixel sensor is divided into two functional regions: a first region for depth measurement and a second region for calibration. This segmentation allows the calibration function to be performed using ambient light in the second region, reducing the need for additional active illumination in the first region and thereby lowering overall power consumption while maintaining depth measurement accuracy.
Solution Approach 2:
The second region of the pixel array serves dual purposes: it acts as a calibration region for determining sensor characteristics and simultaneously functions as an active imaging region during normal operation. This multi-functionality eliminates the need for dedicated calibration hardware, reducing device size and power consumption while enabling runtime calibration capabilities.
2Measurement precision
If conventional CMOS pixel sensors are used for ToF depth measurement, then depth measurement capability is achieved, but device size increases
Solution Approach 1:
The pixel sensor is divided into two functional regions: a first region for depth measurement and a second region for calibration. This segmentation allows the calibration function to be performed using ambient light in the second region, reducing the need for additional active illumination in the first region and thereby lowering overall power consumption while maintaining depth measurement accuracy.
Solution Approach 2:
The second region of the pixel array serves dual purposes: it acts as a calibration region for determining sensor characteristics and simultaneously functions as an active imaging region during normal operation. This multi-functionality eliminates the need for dedicated calibration hardware, reducing device size and power consumption while enabling runtime calibration capabilities.
3Measurement precision
If calibration is performed using dedicated calibration hardware, then calibration accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The second region of the pixel array serves dual purposes: it acts as a calibration region for determining sensor characteristics and simultaneously functions as an active imaging region during normal operation. This multi-functionality eliminates the need for dedicated calibration hardware, reducing device size and power consumption while enabling runtime calibration capabilities.
Solution Approach 2:
The pixel sensor performs calibration using its own second region and ambient light, without requiring external calibration hardware or additional power sources. The sensor self-calibrates by utilizing the ambient light captured in the second region to determine sensor characteristics, thereby simplifying the overall device structure and reducing power consumption.
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 system enables accurate and fast ToF depth measurement with reduced power consumption and sensor overhead, enabling calibration in each frame while maintaining high accuracy and supporting mobile computer vision applications.
Implementation Method 1
a photodiode; a ground contact for coupling a second end of the photodiode to an electrical ground
Data Source
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Figure 2A
Figure 2B
AI summary
An image sensor device includes a plurality of pixel cells arranged in a pixel array, a control circuit for controlling an exposure phase and a sampling phase of the image sensor device. Each of the plurality of pixel cells includes a photodiode, a storage diode, and a floating diffusion region. The control circuit is configured to activate the photodiode in a plurality of time windows to sense light reflected from a target as a result of a corresponding plurality of emitted light pulses, with a pre-determined delay time between each time window and a corresponding emitted light pulse. The photodiode can be activated using a plurality of bias voltage pulses or a plurality of global shutter signal pulses.