Serial Readout Pixel Array for Image Sensor Scalability
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Solution Overview
Problem
As image sensor resolution increases, the size of the pixel array grows, requiring each pixel to drive an increasingly large column bus for parallel readout, which becomes inefficient and limits scalability.
Innovation Solution
The implementation of a serial readout mechanism where pixels are connected in chains, using a comparator and counter with a ramp voltage to convert analog pixel voltages to digital values, allowing bit-serial readout of each row or column without the need for a global counter reset signal, and enabling local interconnections within the pixel array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If parallel readout with column buses is used, then readout speed is improved, but device complexity and area increase with resolution
Solution Approach 1:
The pixel array is divided into groups where pixels within each group share a common readout path. Instead of requiring each pixel to have its own column bus, pixels are segmented into groups that sequentially share readout resources, reducing the total number of interconnects while maintaining readout capability.
Solution Approach 2:
The patent transitions from a two-dimensional parallel readout architecture (with column buses for each pixel column) to a more complex multi-dimensional architecture that incorporates time-sequential access. This allows the system to maintain high readout speeds by utilizing temporal dimension for data transmission while reducing spatial interconnect requirements.
2Measurement precision
If pixel array size increases for higher resolution, then image quality is improved, but each pixel must drive a larger column bus increasing complexity
Solution Approach 1:
The high-resolution pixel array is segmented into multiple groups that share readout resources sequentially. Each group contains a subset of pixels that can be read out through a common path, preventing any single pixel from needing to drive an excessively large column bus while maintaining the overall high resolution capability.
Solution Approach 2:
The readout circuitry is designed with universal, multi-functional components that can serve multiple pixels within a group. The same readout path and associated circuitry are reused sequentially for different pixel groups, reducing the total amount of dedicated circuitry needed for high-resolution operation.
3Productivity
If parallel readout architecture is used, then readout efficiency is improved, but additional readout circuitry and interconnects are required
Solution Approach 1:
Multiple pixel readout paths are merged into shared common paths that are used sequentially by different pixel groups. This combining of resources reduces the total quantity of dedicated readout circuitry and interconnects while maintaining efficient readout capability through time-division multiplexing.
Solution Approach 2:
The pixel array is segmented into groups that share readout resources, allowing the system to achieve parallel readout efficiency within each group while using sequential access between groups. This segmentation strategy reduces the overall circuitry requirements compared to fully parallel readout of all pixels.
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 need for extensive interconnects, eliminates the requirement for additional readout circuitry, and enhances scalability by allowing each pixel to drive only its neighbor, improving the efficiency and area utilization of the image sensor.
Implementation Method 1
each pixel comprising a photo-diode, for providing a pixel voltage
Implementation Method 2
an analog-to-digital converter (ADC) operable to convert the pixel voltage to a digital value
Data Source
AI summary
The image sensor includes an array of pixels, each pixel having a photo-diode, for providing a pixel voltage, an analog-to-digital converter (ADC) operable to convert the pixel voltage to a digital value and a memory for storing the digital value. Read circuitry is included for reading out the digital values from the pixels of the array in a predetermined order. The image sensor may be configured such that a counter incorporates the memory, and the counter may be adapted to operate as a shift register. The counters of two or more pixels may be connected to form one or more chains such that digital values can be read out in a bit-serial manner.