Image Sensor IR Filtering for ToF Depth Accuracy
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Solution Overview
Problem
Time-of-flight (ToF) image sensors face reduced signal-to-noise ratio (SNR) due to ambient infrared (IR) light interference, which contaminates the depth information signal intended for 3D imaging applications.
Innovation Solution
Integration of red (R), green (G), blue (B), and IR pixels in a single image sensor with IR filters at R, G, and B pixels to block IR noise, and an IR pass filter at the IR pixel to isolate pure IR signals, enhancing the SNR of depth information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If IR pixels are integrated with R, G, and B pixels in a single image sensor, then the capability to collect IR signals for 3D imaging is improved, but IR signal noise is generated at the R, G, and B pixels due to IR light reception
Solution Approach 1:
The image sensor is segmented into different pixel types (R, G, B, and IR pixels) with distinct optical filtering characteristics. Each pixel type is designed to respond to specific wavelength ranges, with IR pixels having no IR filter and R, G, B pixels having IR filters to prevent IR noise generation while maintaining their respective color sensing functions.
Solution Approach 2:
Different regions of the image sensor (different pixels) are assigned different optical filtering properties. IR filters are selectively applied only to R, G, and B pixels to block IR light, while IR pixels lack these filters to maximize IR signal reception. This local differentiation allows simultaneous IR signal collection and noise prevention.
2Illumination intensity
If ambient IR light is received by the image sensor, then the sensor can detect ambient light, but the signal-to-noise ratio of depth information is reduced due to contamination of the reflected component
Solution Approach 1:
The sensor array is segmented into dedicated IR pixels for ambient IR light detection and other pixels for depth measurement. By spatially separating these functions, the system can simultaneously monitor ambient IR conditions while maintaining clean depth signals from the modulated light source.
Solution Approach 2:
IR filters act as intermediary elements that selectively block IR wavelengths from reaching R, G, and B pixels while allowing visible light through. This intermediary filtering prevents IR contamination of depth measurements while preserving the functionality of color sensors.
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 prevents IR signal noise at R, G, and B pixels, allowing for the collection of pure IR signals, thereby enhancing the signal-to-noise ratio of depth information in 3D imaging applications.
Implementation Method 1
an IR filter stacked with the R, G and B filters, wherein the IR filter cuts off at least IR light with a specific wavelength
Implementation Method 2
An imaging sensor designed to respond to the same spectrum of the modulated light source receives the light and converts the photonic energy to electrical current
Implementation Method 3
an IR pass filter disposed at the IR pixel
Data Source
AI summary
An image sensor is provided. The image sensor includes a red (R) pixel, a green (G) pixel, a blue (B) pixel and an infrared (IR) pixel, and R, G and B filters respectively disposed at the R, G and B pixels. The image sensor also includes an IR pass filter disposed at the IR pixel and an IR filter stacked with the R, G and B filters, wherein the IR filter cuts off at least IR light with a specific wavelength. Furthermore, a method of forming an image sensor is also provided.