Image Sensor Pixel Array Circulation Gates for Time of Flight Distance Measurement
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Solution Overview
Problem
Current image sensing devices face challenges in accurately measuring distance using the Time of Flight (TOF) method due to limitations in efficiently moving and transferring photocharges within the pixel array, which affects the analysis of time delays based on the distance to a target object.
Innovation Solution
The image sensing device incorporates a pixel array with circulation gates and transfer gates that move and transfer photocharges in a predetermined direction, allowing electrons to circulate and be transferred to floating diffusion regions, enabling effective analysis of time delays by controlling the movement and transfer of electrons in opposite directions within contiguous pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photocharges are moved and transferred within the pixel array using conventional methods, then distance measurement can be performed, but the precision of distance calculation is limited due to inefficient photocharge transfer
Solution Approach 1:
The pixel array is divided into multiple pixel groups, with each group containing multiple pixels that share common circulation gates and transfer gates. This segmentation allows efficient photocharge transfer within each group while maintaining independent operation across groups, thereby improving both transfer efficiency and measurement precision.
Solution Approach 2:
Multiple pixels within each pixel group share common circulation gates and transfer gates, merging their photocharge transfer pathways. This merging reduces the number of separate transfer channels needed, improving overall transfer efficiency while enabling precise time delay measurement through coordinated operation of shared gates.
2Measurement precision
If circulation gates and transfer gates are added to improve photocharge transfer, then distance measurement precision improves, but device complexity increases
Solution Approach 1:
The circulation gates and transfer gates serve multiple functions: they control photocharge transfer within pixel groups, enable time delay measurement for distance calculation, and coordinate operation across multiple pixels. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while achieving improved precision.
3Measurement precision
If adjacent pixels alternate the direction of electron movement, then time delay analysis precision improves, but control complexity increases
Solution Approach 1:
The circulation gates apply periodic voltage changes that alternately move photocharges in opposite directions through adjacent pixels. This periodic action creates the necessary time delay patterns for measurement while using a single control signal source, simplifying the coordination complexity through rhythmic, predictable timing.
Solution Approach 2:
The system measures the time delay between photocharge movement in adjacent pixels and uses this feedback to calculate distance. The control circuit adjusts circulation gate timing based on measured delays, creating a feedback loop that automatically optimizes measurement precision without requiring complex manual coordination.
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 enhances the accuracy and efficiency of distance measurement by improving the movement and transfer of electrons within the pixel array, allowing for more precise analysis of time delays and thus better distance calculation.
Implementation Method 1
a photoelectric conversion element configured to generate photocharges by performing photoelectric conversion of incident light
Data Source
AI summary
The image sensing device includes a pixel array including a plurality of unit pixels arranged in columns and rows. Each unit pixel includes a photoelectric conversion element, circulation gates, transfer gates, and drain nodes. The photoelectric conversion element generates photocharges by performing photoelectric conversion of incident light. The circulation gates are located at sides of the photoelectric conversion element, receive circulation control signals and move the photocharges within the photoelectric conversion element in a predetermined direction based on the circulation control signals. The transfer gates are respectively located between two adjacent circulation gates, receive a transfer control signal and transmit the photocharges to a floating diffusion region based on the transfer control signal. The drain nodes are located at sides of the circulation gates that are opposite to the photoelectric conversion element, and receive a drain voltage. The drain nodes include a first drain node that is shared by two adjacent unit pixels arranged in the first direction and a second drain node that is shared by the two adjacent unit pixels arranged in the second direction.