Analog Histogram Memory Cell for Image Sensor Exposure Cutoff
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Solution Overview
Problem
Conventional analog histogram techniques for depth sensing in artificial reality systems fail to detect saturation, leading to imprecise exposure and inability to limit further exposure of image sensor pixels when saturation occurs.
Innovation Solution
Analog memory cell circuit that automatically detects saturation and stops further exposure of the image sensor by triggering a stop exposure function when a memory cell reaches a maximum value, using a storage capacitor to sense a voltage representing an exposure event and enabling a stop exposure output line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
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 imprecise exposure
Solution Approach 1:
The patent combines the histogram accumulation function and saturation detection function into a single analog memory cell circuit. The memory cell simultaneously performs charge accumulation for histogram binning and saturation detection through its inherent charge storage capability, eliminating the need for separate digital processing circuits and maintaining analog compactness while enabling precision exposure control.
Solution Approach 2:
The patent implements a feedback mechanism where the saturation status of memory cells is continuously monitored and fed back to control the exposure termination. When saturation is detected in any memory cell, this information feedback triggers the stop exposure function, creating a closed-loop control system that automatically adjusts exposure based on real-time saturation conditions.
2Productivity
If exposure continues without saturation detection, then the image sensor operates continuously, but overexposure occurs reducing depth sensing accuracy
Solution Approach 1:
The patent performs preliminary saturation detection within the memory cells during the exposure process itself. By monitoring charge accumulation levels in advance and detecting saturation conditions as they develop, the system can proactively terminate exposure before overexposure occurs, ensuring measurement accuracy is maintained without sacrificing sensing speed.
Solution Approach 2:
The memory cells perform self-service saturation detection using their own charge storage state. The analog circuitry within each memory cell automatically detects when its charge threshold is reached, eliminating the need for external control logic and enabling autonomous exposure termination that maintains both speed and accuracy.
3Measurement precision
If multiple histogram bins are allowed to accumulate charge, then depth information resolution is improved, but saturation occurs in multiple bins reducing precision
Solution Approach 1:
The patent implements comprehensive feedback monitoring across all histogram memory cells simultaneously. Each memory cell's saturation status is continuously fed back to the control logic, which terminates exposure as soon as any cell reaches saturation. This feedback mechanism prevents multiple bins from entering saturation, preserving the precision of depth information across the entire histogram distribution.
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
Prevents overexposure of image sensor pixels, enhancing precision in depth sensing by stopping exposure when saturation is detected, thereby improving the accuracy of depth information generation.
Implementation Method 1
a storage capacitor configured to sense a voltage representing an exposure event
Data Source
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.