ToF Pixel Bias Control for Uniform Distance Image Accuracy
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Solution Overview
Problem
Conventional distance measuring methods using a time of flight (ToF) method in solid-state imaging elements suffer from variations in sensitivity between pixels due to process or temperature variations, leading to distortions in brightness and darkness in distance images and reduced measurement accuracy.
Innovation Solution
A sensing device with pixel circuits that apply a predetermined reverse bias voltage and include a voltage control unit to adjust the bias voltage to match the breakdown voltage of each pixel, using individual and common bias circuits to correct sensitivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common anode potential is applied to all pixels, then the circuit structure is simplified, but sensitivity variations between pixels cannot be corrected
Solution Approach 1:
The patent segments the bias voltage control by providing separate cathode potential control circuits for each pixel while maintaining a common anode potential. This allows individual sensitivity correction for each pixel through dedicated bias voltage adjustment, while keeping the overall circuit structure manageable through the shared anode connection.
Solution Approach 2:
The patent applies local quality by enabling each pixel to have its own cathode potential control circuit that can independently adjust the reverse bias voltage according to that specific pixel's sensitivity characteristics. This localized control allows precise correction of pixel-to-pixel variations without affecting other pixels.
2Measurement precision
If individual bias circuits are provided for each pixel, then sensitivity variations can be corrected, but the circuit complexity increases
Solution Approach 1:
The patent segments the bias control function into common anode potential control and individual cathode potential control circuits. This segmentation allows the system to achieve precise pixel-level sensitivity correction while maintaining circuit simplicity through the shared anode connection, avoiding the need for completely independent control circuits for each pixel.
3Ease of manufacture
If the reverse bias voltage is not adjusted per pixel, then the manufacturing process is simpler, but sensitivity variations cause shading noise in distance images
Solution Approach 1:
The patent implements preliminary action by measuring and storing the breakdown voltage for each pixel during the manufacturing process, and using this pre-acquired data to configure the individual cathode potential control circuits. This allows sensitivity variations to be compensated for before the device is deployed, eliminating shading noise without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The patent applies parameter changes by adjusting the reverse bias voltage parameter for each pixel based on its measured breakdown voltage characteristics. By changing the bias voltage parameter to match each pixel's specific electrical characteristics, the system corrects sensitivity variations and eliminates shading noise while maintaining manufacturing simplicity.
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 solution effectively corrects sensitivity variations between pixels, reducing shading noise and improving distance measurement accuracy by uniformly distributing heat and adjusting bias potentials for each pixel.
Implementation Method 1
a photoelectric conversion element to which a predetermined reverse bias voltage is applied between an anode and a cathode
Implementation Method 2
a voltage control unit that adjusts the reverse bias voltage to a value corresponding to a breakdown voltage of the photoelectric conversion element for each of the pixel circuits
Data Source
AI summary
In a sensing device that generates a distance image, a variation in distance measurement accuracy in the distance image is reduced. The sensing device includes a predetermined number of pixel circuits and a voltage control unit. Each of the predetermined number of pixel circuits includes a photoelectric conversion element and a detection circuit. A predetermined reverse bias voltage is applied between an anode and a cathode of the photoelectric conversion element. The detection circuit detects whether a photon is present or absent on the basis of a potential of either the anode or the cathode. The voltage control unit adjusts the reverse bias voltage to a value corresponding to a breakdown voltage of the photoelectric conversion element for each of the pixel circuits.