Active Pixel Array for Time of Flight Detector Distance Measurement
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Solution Overview
Problem
Current LiDAR systems for vehicle autonomy face challenges in accurately detecting the distance of objects using time-of-flight measurements due to the partial reception of reflected light pulses within a limited time slot, leading to incomplete data for distance calculation.
Innovation Solution
An active pixel array with two floating diffusion regions and a controller that allows independent readouts at different timepoints, enabling the detection of both the front and back portions of light pulses, thereby providing complete data for distance calculation using multiple photodiodes arranged in columns and rows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single readout is performed at the end of each emitted pulse, then the readout timing is simple, but only a front section of the reflected pulse is detected, resulting in incomplete distance measurement data
Solution Approach 1:
The pixel structure is segmented into two separate floating diffusion regions (first and second floating diffusion regions) that can independently read out charges at different timepoints. This segmentation allows the detector to capture both the front section (S1) and remaining portion (S2) of the reflected pulse separately, enabling complete distance measurement data to be obtained while maintaining a relatively simple pixel structure without requiring complex external timing control circuitry
2Loss of information
If the readout is performed only at the end of the emitted pulse time slot, then the readout operation is simple, but the remaining portion of the reflected pulse is lost, reducing measurement completeness
Solution Approach 1:
The first floating diffusion region performs a preliminary readout of charges at an first timepoint during the pulse duration, capturing the front section of the reflected pulse. The second floating diffusion region then performs a second readout at a second timepoint, capturing the remaining portion. This preliminary action approach ensures complete information capture while keeping each individual readout operation simple and independent
3Measurement precision
If multiple floating diffusion regions are added to enable multi-timepoint readout, then complete pulse detection is achieved, but the pixel structure complexity increases
Solution Approach 1:
Multiple floating diffusion regions are merged within a single pixel element, sharing common components such as the photodiode and microlens structure. This merging approach enables multi-timepoint readout capability while minimizing the increase in pixel structure complexity, as the additional floating diffusion regions integrate into the existing pixel architecture rather than requiring entirely separate detector elements
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 allows for precise calculation of object distance by reading different portions of light pulses at distinct timepoints, enhancing the accuracy and resolution of LiDAR systems in vehicle autonomy applications.
Implementation Method 1
an active area including at least one photodiode being configured to detect light pulses having a predefined time duration
Data Source
AI summary
An active pixel sensor having an array of pixel elements arranged in columns is provided. Each pixel element including: an active area including at least one photodiode being configured to detect light pulses having a predefined time duration; a first and second floating diffusion region coupled to the active area and being configured for readout of charges accumulating in the active area; a controller configured to independently control the readout of the first and the second floating diffusion regions, and to conduct a first readout of the active area by the first floating diffusion region and a second readout of the active area by the first floating diffusion region; wherein the first readout is conducted at a first timepoint with respect to the time duration and the second readout is conducted at a second timepoint with respect to the time duration.