Solid-State Imaging Pixel With Segmented Floating Diffusion For Noise Removal
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Solution Overview
Problem
Existing solid-state imaging elements face challenges in achieving satisfactory signal-to-noise ratio (S/N) in both high and low brightness modes while effectively removing reset noise, particularly due to limitations in pixel configuration and signal processing methods.
Innovation Solution
A solid-state imaging element with a pixel structure that includes a photoelectric conversion portion, transmission portion, detection portions, reset portion, connection/separation control portion, and output portion, which generates first and second pixel signals by calculating differences between connection-state and separation-state reset and output signals, allowing for appropriate noise removal without the need for addition processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the capacity of floating diffusion (FD) is increased to increase the amount of usable charges, then the amount of charges increases, but the signal-to-noise ratio (S/N) deteriorates
Solution Approach 1:
The floating diffusion is divided into two separate capacitors (FD1 and FD2) with different capacities. FD1 has a smaller capacity optimized for low brightness mode to achieve high gain and good S/N, while FD2 has a larger capacity optimized for high brightness mode to accommodate large charge amounts. This segmentation allows each capacitor to be optimized for its specific operating range, resolving the trade-off between charge amount and S/N ratio.
2Object-generated harmful factors
If a difference calculation method is used to remove reset noise, then reset noise removal is achieved, but reset noise cannot be completely removed in both signals
Solution Approach 1:
Reset level signals (N1 and N2) are obtained in advance by resetting the respective capacitors before the actual signal measurement. These preliminary reset level measurements are then used in difference calculations to remove reset noise from the corresponding signal measurements. By performing the reset operation and measuring reset levels beforehand, the system can accurately subtract reset noise from both S1 and S2 signals, completely removing reset noise effects.
3Adaptability or versatility
If an addition process is performed to obtain high brightness mode signal, then the signal range is extended, but signal linearity deteriorates and noise increases
Solution Approach 1:
The system dynamically selects which capacitor to use based on the brightness level of the input signal. A selection circuit determines whether to use FD1 (for low brightness mode) or FD2 (for high brightness mode) based on real-time signal conditions. This dynamic selection allows the system to adapt to different brightness levels without requiring addition processes, thereby extending the usable signal range while maintaining signal linearity and avoiding noise increases associated with signal addition.
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 approach enables satisfactory S/N in both high and low brightness modes and effectively removes reset noise, improving image quality without deteriorating signal linearity or increasing noise.
Implementation Method 1
a signal is extracted in such a manner that a charge of the photodiode (PD) is transferred
Data Source
AI summary
A pixel includes detection portions which detect transferred charges, a reset portion which resets the plurality of detection portions, a connection/separation control portion which controls connection and separation of the detection portions, and an output portion which outputs a signal corresponding to the potential of a detection portion. In a state where the connection/separation control portion connects the detection portions, the output portion outputs a connection-state reset level signal and a connection-state output signal and, in a state where the connection/separation control portion separates the detection portions, the output portion outputs a separation-state reset level signal and a separation-state output signal. A first pixel signal is generated by a difference between the connection-state reset level signal and the connection-state output signal, and a second pixel signal is generated by a difference between the separation-state reset level signal and the separation-state output signal.