Image Sensor Memory Cell Saturation Detection for Depth Sensing
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Solution Overview
Problem
Conventional analog histogram techniques for depth sensing in artificial reality systems are unable to detect saturation, leading to overexposure of image sensor pixels and reduced precision in depth measurement.
Innovation Solution
An analog memory cell circuit is introduced that automatically detects saturation in image sensor pixels, triggering a stop exposure function to prevent further exposure when a maximum value is reached, using a storage capacitor and stop exposure circuit to manage exposure events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional analog histogram techniques are used for depth sensing, then the system remains compact and energy efficient, but saturation detection capability is lost leading to overexposure
Solution Approach 1:
The patent combines the saturation detection function with the existing memory cell structure by integrating a stop exposure circuit into each memory cell. This merging approach allows the system to gain saturation detection capability without adding separate dedicated saturation detection hardware, thus maintaining compactness while improving reliability.
Solution Approach 2:
The patent implements a feedback mechanism where the storage capacitor monitors its own charge level and triggers a stop exposure signal when saturation is detected. This self-monitoring feedback loop enables automatic saturation detection and prevents overexposure without requiring external control circuits, balancing reliability improvement with minimal complexity increase.
2Productivity
If exposure continues without saturation detection, then the image sensor captures more light events, but pixel overexposure occurs reducing depth measurement precision
Solution Approach 1:
The patent prepares the stop exposure circuit in advance within each memory cell, so that when saturation occurs, the system can immediately stop exposure without delay. This preliminary preparation of the stop mechanism ensures that productivity is maximized during the exposure window while preventing any precision loss from overexposure.
Solution Approach 2:
The memory cell's storage capacitor serves dual purposes: it accumulates charge from light events during exposure and simultaneously monitors its own saturation level. This self-service capability allows the system to maintain high productivity by continuously capturing events while autonomously detecting when to stop, thereby preserving measurement precision.
3Quantity of substance
If multiple histogram bins are allowed to reach saturation, then more depth information is accumulated, but precision is reduced due to overexposure
Solution Approach 1:
The patent divides the histogram accumulation function across multiple independent memory cells, each with its own stop exposure circuit. This segmentation allows the system to accumulate data from multiple bins efficiently while each cell independently monitors its own saturation, preventing the precision loss that would occur if multiple bins were allowed to overexpose simultaneously.
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 solution prevents overexposure and enhances the precision of depth sensing by accurately stopping exposure when saturation is detected, improving the accuracy of depth measurements in artificial reality systems.
Implementation Method 1
a storage capacitor configured to sense a voltage representing an exposure event
Data Source
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AI summary
This disclosure describes a method of operating an image sensor and a plurality of memory cells associated with the image sensor, each memory cell comprising: one or more input lines, a stop exposure output line; a storage capacitor; and a stop exposure circuit. The method may comprise, by each of the memory cells, sensing a voltage representing an exposure event in response to the input lines being enabled, and by a first one of the memory cells, enabling the stop exposure output line in response to a charge on the storage capacitor satisfying a charge threshold; and stopping further exposure of the image sensor in response to the stop exposure output line being enabled for the first one of the memory cells.