Pixel With Normally-On Transistor For Dynamic Range
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Solution Overview
Problem
Existing image sensor pixels face a trade-off between dynamic range and power consumption, where increasing dynamic range typically leads to higher power usage, and reducing consumption often results in lower dynamic range.
Innovation Solution
The design incorporates a normally on transistor with a buried channel configuration and a charge transfer device, allowing for increased dynamic range without increasing the maximum potential supplied to the pixel, by optimizing the initialization and reading phases of the detection node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the maximum potential supplied to the pixel is increased to increase its dynamic range, then the dynamic range is improved, but the power consumption is increased
Solution Approach 1:
The patent changes the operational parameters of the pixel by introducing a normally-on transistor that operates at lower potentials. The detection node is initialized to a first potential (e.g., 0V) and reads out at a second potential (e.g., -0.7V), allowing the pixel to achieve sufficient dynamic range without requiring high supply voltages. This parameter optimization enables reduced power consumption while maintaining adequate dynamic range performance.
2Use of energy by moving object
If the maximum potential supplied to the pixel is reduced to decrease power consumption, then the power consumption is reduced, but the dynamic range is reduced
Solution Approach 1:
The patent employs dynamic control of the detection node potential through the normally-on transistor. The transistor remains conductive throughout operation, allowing the detection node to dynamically switch between the first potential (initialization) and the second potential (reading). This dynamic operation enables the pixel to maintain adequate dynamic range even with reduced supply potentials, as the full swing between the two potentials is utilized for signal detection.
Data Source
AI summary
A pixel includes: a detection node; a first normally on transistor connected between the detection node and a rail for applying a first potential; and a second transistor whose gate is connected to the detection node. An image sensor includes a plurality of the pixels and a control circuit configured to apply, during for a phase of initializing the detection node, the first potential to the gate of the first transistor.