Imaging Device Variable Capacitance Dynamic Range
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Solution Overview
Problem
Existing imaging devices face challenges in varying the capacitance value of the input node of an amplifying transistor, which affects the dynamic range and signal-to-noise ratio, particularly when handling high-luminance signals.
Innovation Solution
The implementation of a capacitance structure with a p-n junction formed by semiconductor regions of specific conductivity types, where the doping impurity concentration of the p-type semiconductor region at the p-n junction interface of the capacitance is higher than that of the photoelectric converter, allowing the capacitance value to be switched between connected and disconnected states, thereby adjusting the charge-voltage conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a capacitance is connected to the floating diffusion to increase the dynamic range, then the dynamic range is improved, but the signal-to-noise ratio deteriorates due to increased capacitance value
Solution Approach 1:
The capacitance value of the input node is made variable by switching the connection state of the capacitance. The pixel includes a switching transistor that connects or disconnects the capacitance (formed by a p-n junction) to the floating diffusion, allowing the capacitance value to be dynamically adjusted between different states to optimize for either dynamic range or signal-to-noise ratio depending on lighting conditions
Solution Approach 2:
The capacitance value is changed by altering the connection state of the capacitance element. By switching between connected and disconnected states, the total capacitance at the input node changes, which directly affects the charge-voltage conversion efficiency and allows optimization of the pixel's response to different luminance levels
2Stability of the object's composition
If the capacitance value is increased to handle high-luminance signals, then the dynamic range is improved, but the saturation point is reached faster reducing sensitivity for low-luminance signals
Solution Approach 1:
The system dynamically switches between different capacitance values based on the luminance level. For high-luminance signals, the capacitance is connected to increase the dynamic range and prevent saturation. For low-luminance signals, the capacitance is disconnected to maintain high sensitivity and signal-to-noise ratio. This dynamic adaptation allows the pixel to optimize its performance for the current lighting condition
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
This configuration enhances the dynamic range and improves the signal-to-noise ratio by adjusting the capacitance value, preventing saturation during high-luminance signals and reducing noise, while maintaining sensitivity.
Implementation Method 1
a photoelectric converter including a p-n junction formed of a first semiconductor region and a second semiconductor region and for accumulating signal carriers in the second semiconductor region
Implementation Method 2
a capacitance including a p-n junction formed of a third semiconductor region and a fourth semiconductor region
Data Source
AI summary
An imaging device includes pixels each of which includes a photoelectric converter including a p-n junction formed of a first semiconductor region and a second semiconductor region, an amplifying transistor configured to amplify a signal based on signal carriers, and a capacitance including a p-n junction formed of a third semiconductor region having the same conductivity type as the first semiconductor region and a fourth semiconductor region having the opposite conductivity type to the third semiconductor region. A doping impurity concentration of an impurity of the same conductivity type as the conductivity type of the third semiconductor region at the p-n junction interface of the capacitance is higher than a doping impurity concentration of an impurity of the same conductivity type as the conductivity type of the first semiconductor region at the p-n junction interface of the photoelectric converter.