Per-Pixel Digital Image Sensor for Global Shutter and Low Power
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Solution Overview
Problem
Current image sensors for applications like virtual reality and augmented reality systems require high speed, high dynamic range, high sensitivity, high resolution, and low power consumption, but existing technologies face limitations in achieving these criteria, particularly with rolling shutter methods that result in limited speed and sensitivity due to shared ADCs and limited exposure time.
Innovation Solution
The development of digital pixel image sensors with a digitizer in each pixel, including a photodiode, transfer gate, analog storage device, and digital memory, utilizing a comparator with a pre-charging circuit to reduce power consumption and implement a global shutter for simultaneous exposure and digitization of all pixels, along with correlated double sampling to reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rolling shutter method with shared ADCs is used, then device complexity is reduced, but imaging speed and sensitivity are limited
Solution Approach 1:
The patent divides the image sensor into independent digital pixels, each with its own photodiode, charge storage device, and digitizer. This segmentation allows simultaneous exposure and digitization across all pixels, eliminating the sequential processing bottleneck of rolling shutter methods and significantly improving imaging speed.
Solution Approach 2:
Each digital pixel is self-contained with its own digitizer that can independently convert analog signals to digital values. This self-service capability eliminates the need for shared ADCs and external processing, enabling parallel operation of all pixels and dramatically increasing frame rate.
2Device complexity
If rolling shutter method with shared ADCs is used, then device complexity is reduced, but sensitivity is limited
Solution Approach 1:
By segmenting the sensor into independent digital pixels with individual charge storage devices and digitizers, the patent enables simultaneous exposure of all pixels. This eliminates the sequential readout limitation of rolling shutter, allowing maximum exposure time for each pixel and significantly improving sensitivity.
3Use of energy by moving object
If pre-charging circuit is used in comparator, then power consumption is reduced, but circuit complexity increases
Solution Approach 1:
The comparator uses a pre-charging circuit that operates periodically rather than continuously. The capacitor is charged only during the brief comparison interval, then discharged and remains inactive during pixel integration. This periodic operation dramatically reduces average power consumption while the simplicity of the capacitor-based circuit keeps added complexity minimal.
4Speed
If digital pixel with per-pixel digitizer is used, then imaging speed and resolution are improved, but device complexity increases
Solution Approach 1:
The patent segments the image sensor into independent digital pixels, each containing a photodiode, charge storage device, and digitizer. This segmentation enables parallel processing of all pixels simultaneously, dramatically improving imaging speed and resolution despite the increased number of components per pixel.
Solution Approach 2:
Each digital pixel is designed with localized functionality including its own digitizer and charge storage device. This local quality approach allows each pixel to operate independently and simultaneously, achieving high-speed imaging while keeping each pixel's circuitry compact and efficient.
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 enables high-speed, high-resolution imaging with low power consumption, increased sensitivity, and reduced noise, addressing the limitations of existing technologies by allowing all pixels to be exposed and digitized simultaneously, thereby improving frame rate and dynamic range.
Implementation Method 1
a photodiode configured to generate charges in response to an optical signal
Data Source
AI summary
Disclosed herein are techniques for digital imaging. A digital pixel image sensor includes a digitizer in each pixel of a plurality of pixels, where the digitizer digitizes analog output signals from a photodiode of the pixel using a comparator, a global reference ramp signal, and a clock counter. In some embodiments, the comparator includes a pre-charging circuit, rather than a constant biasing circuit, to reduce the power consumption of each pixel. In some embodiments, each pixel includes a digital or analog correlated double sampling (CDS) circuit to reduce noise and provide a higher dynamic range.