Dual Gain Image Sensor Pixel Readout Method for Electrical Offset Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors with dual-gain readout modes experience electrical crosstalk and require multiple analog-to-digital conversions and a frame buffer, leading to increased power consumption and hardware requirements, which results in undesirable electrical offsets and reduced dynamic range.
Innovation Solution
The implementation of a dual gain image sensor pixel readout method that reduces electrical offsets by reading signals in a high gain configuration without a frame buffer, using a three or four read method to minimize ADC conversions and eliminate the need for a frame buffer, while ensuring all signals have the same electrical offset for optimized pixel output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If dual gain pixels read out captured high-gain and low-gain image data in respective configurations, then dynamic range is improved, but electrical crosstalk causes large electrical offset between signals
Solution Approach 1:
The patent applies preliminary action by reading out the low-gain signal before the high-gain signal, and storing the low-gain reset voltage in a frame buffer before the high-gain readout begins. This timing sequence prevents electrical crosstalk between the two readout operations while maintaining both gain modes for extended dynamic range. The frame buffer stores calibration data that compensates for any residual offset.
Solution Approach 2:
The frame buffer acts as an intermediary element between the dual gain readout operations. It stores the low-gain reset voltage and provides it during high-gain readout, effectively mediating the interaction between the two signal paths to eliminate electrical crosstalk and offset errors without requiring physical isolation of the readout circuits.
2Manufacturing precision
If four pixel read operations and ADC conversions are used to operate without frame buffer, then electrical offset is reduced, but power consumption increases
Solution Approach 1:
The frame buffer stores the low-gain reset voltage and makes it available during high-gain readout without requiring additional read operations. The system uses the stored calibration data to compensate for offset, making the frame buffer self-sufficient and eliminating the need for extra ADC conversions that would increase power consumption.
3Use of energy by moving object
If three pixel reads and ADC conversions are used with frame buffer, then hardware requirements increase, but power consumption is reduced
Solution Approach 1:
The frame buffer serves multiple functions: it stores calibration data for offset compensation, provides reference voltages for both gain modes, and enables precise timing control of the readout sequence. This multi-functionality reduces the need for separate dedicated circuits for each function, effectively reducing overall hardware complexity despite the additional buffer memory.
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 reduces the number of ADC conversions and eliminates the need for a frame buffer, minimizing power consumption and hardware requirements, while improving the dynamic range and signal-to-noise ratio by ensuring all pixel output signals are within the operational range of the analog readout circuitry.
Implementation Method 1
accumulating charge in response to incident light with a photodiode in a pixel
Implementation Method 2
transferring charge from the photodiode to a floating diffusion node with a transfer transistor
Implementation Method 3
distributing the accumulated charge between the floating diffusion node and the gain select storage node with the gain select transistor
Implementation Method 4
resetting the floating diffusion node and the gain select storage node to a pixel voltage with a reset transistor
Data Source
AI summary
An imaging system may include an image sensor having an array of dual gain pixels. Each pixel may be operated using an improved three read method and an improved four read method such that all signals are read in a high gain configuration in order to prevent electrical offset in signal levels. Each pixel may be operated using an improved three read, two analog to digital conversion (ADC) method in which a frame buffer is used to store calibration data. Each pixel may be operated using an improved three read, three ADC method in which no frame buffer is required. A high dynamic range image signal may be produced for each pixel based on signals read from the pixel and on light conditions.