Solid-State Imaging Device Pixel Circuit for Distance Measurement
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Solution Overview
Problem
The pulse phase method for solid-state imaging devices has a narrow dynamic range and poor tolerance to strong background light, leading to saturation and inaccurate distance measurement due to the intensity of received light being proportional to the square of the distance, and increased optical shot noise from background light.
Innovation Solution
A solid-state imaging device with a configuration of light receiving, counter, comparison, and storage circuits each including a transistor of a first conductivity type, allowing for a wide measurable distance range and accurate distance measurement even under strong background light conditions, without the need for a well for transistors of a different conductivity type, thereby reducing pixel area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pulse phase method is used to measure distance, then distance measurement capability is achieved, but the dynamic range is narrow and saturation occurs for close objects
Solution Approach 1:
The patent applies dynamics by making the integration period variable rather than fixed. The integration period is dynamically adjusted based on the expected distance range, allowing the system to adapt to both close and remote objects. This resolves the contradiction by enabling the same system to handle varying distance scales without saturation, effectively expanding the dynamic range while maintaining measurement precision.
Solution Approach 2:
The patent changes the parameter of integration period based on distance conditions. By modifying the integration period parameter according to the expected object distance, the system can optimize its response for different ranges. This parameter change allows the system to avoid saturation for close objects while maintaining sensitivity for remote objects, thus expanding the usable dynamic range.
2Measurement precision
If the pulse width of projection light is increased to extend measurement range, then measurable distance range is improved, but optical shot noise from background light increases
Solution Approach 1:
The patent applies dynamics by making the integration period variable rather than fixed. The integration period is dynamically adjusted based on the expected distance range, allowing the system to adapt to both close and remote objects. This resolves the contradiction by enabling the same system to handle varying distance scales without saturation, effectively expanding the dynamic range while maintaining measurement precision.
Solution Approach 2:
The patent substitutes the conventional approach of extending measurement range by increasing light pulse width with an alternative method based on variable integration period. Instead of mechanically increasing the light pulse duration, the system uses temporal gating and variable integration windows to achieve extended range measurement. This substitution allows range extension without proportionally increasing background light integration and associated shot noise.
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 provides a solid-state imaging device with a wide measurable distance range and improved tolerance to strong background light, enabling accurate distance measurement and reducing the area of each pixel.
Implementation Method 1
a light receiving circuit that includes a light receiving element and outputs a light reception signal, the light reception signal changing in accordance with whether or not incident light arrives at the light receiving element in a light exposure period
Data Source
AI summary
A solid-state imaging device including a plurality of two-dimensionally arranged pixels is provided. The pixels each include a light receiving circuit that senses incident light having arrived at the light receiving element in a light exposure period, a counter circuit that counts the number of arrivals of the incident light based on the light reception signal from the light receiving circuit, a comparison circuit that outputs a comparison signal according to the count from the counter circuit, and a storage circuit that stores a time signal as a distance signal when the comparison signal from the comparison circuit is ON. Transistors included in the light receiving circuit, the counter circuit, the comparison circuit, and the storage circuit have the same conductivity type.