Transfer-Gate Pixel With Dual Sampling for Background Light Cancellation
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Solution Overview
Problem
Conventional CMOS image sensors struggle with strong background lighting due to limited dynamic range, leading to low signal-to-noise ratio and requiring additional power-consuming post-processing for background subtraction.
Innovation Solution
A pixel design with two sample stages that operate in conjunction with a light source to capture optical information at different illumination levels, enabling in-pixel background light cancellation during image acquisition, thus eliminating the need for off-chip data buffers and improving contrast and detection probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the power of the light source is increased to overcome strong background lighting, then the signal-to-noise ratio is improved, but the power consumption increases
Solution Approach 1:
The pixel performs preliminary sampling of the background signal before the main signal acquisition. The first sample stage captures the background illumination level, which is then subtracted from the total signal in the second sample stage, enabling effective background cancellation without increasing light source power
Solution Approach 2:
The signal acquisition process is segmented into multiple sampling stages. The first sample stage is dedicated to capturing background signal, while the second sample stage captures the total signal including both background and object signal. This segmentation allows separate processing and subtraction of background components
2Measurement precision
If background subtraction is performed in post-processing, then the image quality is improved, but additional circuitry and computational power are required
Solution Approach 1:
The background subtraction function is merged with the signal sampling process itself. Both background sampling and total signal sampling occur within the same pixel structure using shared components (photosensitive element, transfer gate, sense node, buffer amplifier), eliminating the need for separate post-processing circuitry
Solution Approach 2:
The pixel performs its own background cancellation operation autonomously during the sampling phase. The dual sample stages within each pixel independently capture and hold background and total signal values, enabling self-service background subtraction without requiring external processing resources
3Measurement precision
If multiple exposures are used for background subtraction, then the contrast and detection probability are improved, but the power consumption increases
Solution Approach 1:
The sampling process uses periodic action by sequentially activating different sample stages based on control signals. The first sample stage samples during a background-only exposure period, then the second sample stage samples during a total signal exposure period, enabling multiple exposure effects through time-sequential periodic sampling
Solution Approach 2:
The background signal is captured in advance during a preliminary sampling phase before the main signal acquisition. This preliminary action of capturing background information allows the system to perform subtraction without requiring additional power-intensive post-processing or multiple full exposures
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 proposed pixel structure enhances image quality by synchronizing exposures with a light source to perform background subtraction on-chip, reducing power consumption and computational requirements while maintaining image clarity.
Implementation Method 1
a photosensitive element for generating charges in response to incident radiation
Data Source
AI summary
A pixel includes a transfer gate, and a sample structure having a first sample stage and a second sample stage. The transfer gate and the first and the second sample stages are configured to be operated in conjunction with a light source in response to a control signal. The first sample stage is configured to sample a first sample value that depends on radiation incident on the photosensitive element from an object or a scene that is illuminated by the light source emitting light at a first output power, while the second sample stage is configured to sample a second sample value that depends on radiation incident on the photosensitive element from the object or the scene that is illuminated by the light source emitting light at a second output power. The first output power is different, in particular significantly different, from the second output power.