TOF Distance Imaging Pulse Control for Linearity and Resolution
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Solution Overview
Problem
Indirect TOF sensors face challenges in improving comprehensive performance, such as distance resolution and linearity, due to issues like nonlinearity of pixel source follower amplifiers and distortion of optical pulses, which are exacerbated when attempting to enhance distance resolution with shorter measurement light pulses.
Innovation Solution
A distance image capturing device with a pixel circuit unit array and peripheral circuit that controls transfer control pulses based on the magnitude relationship between charges accumulated in different areas, using time-domain feedback control and Delta Sigma modulation to reduce charge amount bias and quantization errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the irradiation time of measurement light is shortened to increase distance resolution, then distance resolution is improved, but linearity is impaired due to nonlinearity of pixel source follower amplifier and distortion of optical pulse
Solution Approach 1:
The pixel array is divided into multiple pixel units, each with dedicated transfer control circuits. By segmenting the charge transfer control into multiple independently controllable units, the system can apply different transfer timing to different pixel regions, compensating for timing errors and maintaining linearity across the entire array even when using short pulse widths for high distance resolution
Solution Approach 2:
The transfer control pulse timing is made dynamic and adjustable rather than fixed. The system can optimize transfer timing based on the specific pulse width being used, allowing the transfer control to adapt to different measurement conditions. This dynamic adjustment compensates for the nonlinearity introduced by short pulses while maintaining the ability to achieve high distance resolution
2Measurement precision
If short pulsed measurement light is used to improve distance resolution, then distance resolution increases, but comprehensive performance deteriorates due to multiple distortion factors
Solution Approach 1:
The system incorporates feedback mechanisms where the transfer control timing is adjusted based on measured performance characteristics. By monitoring the actual charge transfer accuracy and timing, the system can compensate for distortions and maintain reliable operation even with short pulses, thereby improving comprehensive performance while preserving high distance resolution
Solution Approach 2:
The system optimizes multiple parameters simultaneously including pulse width, transfer control timing, and integration time. By carefully coordinating these parameters rather than relying on a single parameter, the system achieves high distance resolution while maintaining comprehensive performance through balanced optimization of all critical factors
3Device complexity
If conventional transfer control is used in indirect TOF sensor, then device complexity is reduced, but charge amount bias and quantization errors increase
Solution Approach 1:
The pixel array is divided into multiple pixel units with dedicated transfer control circuits. This segmentation allows independent optimization of charge transfer timing for each unit, reducing charge amount bias and quantization errors through precise local control while keeping each individual circuit unit relatively simple
Solution Approach 2:
The transfer control timing is pre-optimized and pre-configured for each pixel unit based on expected operating conditions. This preliminary setup of transfer timing reduces the need for complex real-time adjustments while minimizing charge amount bias and quantization errors, achieving high precision with moderate circuit complexity
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
The device achieves high linearity and distance resolution over a wide range by reducing charge amount bias and quantization errors, enabling precise measurement of light flight time through coarse and fine measurement techniques.
Implementation Method 1
a pixel circuit unit includes a photoelectric conversion area for converting light into the charge
Implementation Method 2
The time required for the measurement light to reach the image capturing target object from the distance image capturing device can be known. The time is also referred to as a light flight time.
Data Source
AI summary
A distance image capturing device includes a light source, a photodiode configured to generate a charge corresponding to received light, and a peripheral circuit configured to control an operation of the pixel circuit unit, in which the peripheral circuit generates a first transfer control pulse and a second transfer control pulse based on the magnitude relationship between a first charge amount accumulated in a first floating diffusion unit and a second charge amount accumulated in a second floating diffusion unit.