Row Decoder for High Dynamic Range Image Sensor
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Solution Overview
Problem
Conventional image sensors, particularly CMOS image sensors, face challenges in achieving high dynamic range imaging due to limited well-capacity and fixed exposure times, making it difficult to perform effectively across a wide range of lighting conditions.
Innovation Solution
The implementation of a high dynamic range image sensor with row decoder circuitry and select circuits that provide in-frame multi-bit exposure control, using encoded precharge offset signals to improve dynamic range performance and reduce the number of wires and metal routings, allowing for individual exposure control of each pixel circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional CMOS image sensors use fixed exposure times, then the device complexity is low, but the dynamic range is limited
Solution Approach 1:
The pixel array is divided into multiple rows, each capable of independent exposure control. The row decoder segments the control signals to different row groups, allowing different exposure times for different rows within the same frame, thereby achieving high dynamic range without requiring complex per-pixel control circuits
Solution Approach 2:
The patent implements dynamic exposure control where the exposure time can be adjusted for different rows based on lighting conditions. The row decoder dynamically selects which rows receive precharge signals at different times, enabling the system to adapt to varying light levels across different spatial regions of the image sensor
2Adaptability or versatility
If multiple successive exposures are used to achieve HDR, then the dynamic range is improved, but the frame rate decreases
Solution Approach 1:
The patent applies preliminary action by precharging certain rows before the actual exposure period. Rows designated for high-light capture receive precharge signals that reset their photodiodes earlier, allowing them to capture shorter exposure times. This preliminary preparation enables multiple effective exposures to be captured within a single frame period, maintaining high frame rates while achieving HDR
Solution Approach 2:
The imaging system uses periodic precharge and readout cycles for different row groups. The row decoder periodically activates precharge signals for alternating rows or row groups, creating a time-multiplexed exposure scheme where different rows capture different exposure durations in a repeating pattern, effectively achieving multi-exposure HDR at high frame rates
3Adaptability or versatility
If individual pixel exposure control is implemented, then the dynamic range performance is improved, but the number of wires and metal routings increases
Solution Approach 1:
The patent merges the exposure control functionality into shared row decoder circuits that serve multiple pixels. Instead of providing independent control lines to each pixel, the row decoder combines control signals for groups of rows, and pixels within each row share common control lines. This merging approach enables individual row exposure control while significantly reducing the total number of wires and metal routings required
Solution Approach 2:
The row decoder acts as an intermediary between the central control logic and the pixel arrays. It receives compact control signals and expands them into row-specific precharge and readout signals, mediating the control distribution to achieve fine-grained exposure control without requiring direct complex routing to each pixel. This intermediary layer simplifies the overall wiring architecture while maintaining precise control capability
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 solution enables improved charge integration across the pixel array, achieving high frame rates and spatial resolution by allowing individual in-frame exposure control for each pixel circuit, thus enhancing the dynamic range imaging capability.
Implementation Method 1
a pixel circuit in a pixel array adapted to accumulate image charge in response to incident light during an integration period
Data Source
AI summary
A pixel circuit includes a transfer transistor coupled between a photodiode and a floating diffusion to transfer image charge to the floating diffusion. A precharge offset signal is representative of a difference between a row that includes the transfer transistor and a different row that is being read out. The selection circuit is coupled to select between first and second transfer control signals to control the transfer transistor. The selection circuit is coupled to output the first transfer control signal in response to a precharge enable signal during a read out operation of the different row. The precharge enable signal is generated in response to a comparison of a precharge offset signal and an exposure value signal. The selection circuit is coupled to output the second transfer control signal in response to a sample enable signal during a read out operation of the row that includes the transfer transistor.