Pipelined Column ADC Architecture for Image Sensor Readout Speed
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Solution Overview
Problem
Conventional image sensor readout circuitry is limited by serialized sample and conversion periods, leading to reduced readout speed due to idle time of column amplifiers and switches during each pixel cell's readout process.
Innovation Solution
Implementing a pipelined column ADC architecture with decoupled pipeline ramp ADCs, where column amplifiers continuously sample data from multiple pixel cells and feed it to parallel pipeline stages for simultaneous sampling and conversion, reducing idle time and enhancing readout speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If serialized sample and conversion periods are used in conventional readout circuitry, then circuit simplicity is maintained, but readout speed is reduced due to idle time of column amplifiers and switches
Solution Approach 1:
The readout circuit is segmented into multiple independent pipeline stages (first pipeline stage with first column ADC, second pipeline stage with second column ADC). Each stage can operate independently and simultaneously, eliminating the idle time problem in serialized architectures while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
The first pipeline stage performs sampling and conversion operations in advance while the second pipeline stage is being set up or is operating in parallel. This preliminary action allows continuous data flow without idle periods, as one stage is always ready to process data while another is completing its cycle.
2Productivity
If continuous data sampling and conversion are implemented using pipelined column ADCs, then readout speed is significantly increased, but circuit architecture becomes more complex
Solution Approach 1:
The pipelined column ADC architecture ensures continuous useful action by maintaining multiple pipeline stages that operate in parallel. While one stage is sampling, another is converting, and a third is outputting data, eliminating idle time and maximizing productivity throughout the readout process.
Solution Approach 2:
The patent transitions from a single-dimensional serialized processing approach to a multi-dimensional parallel pipeline architecture. By adding the time dimension through overlapping operations across multiple stages, the system achieves continuous processing without proportionally increasing overall system complexity.
3Loss of time
If parallel pipeline stages with multiple column ADCs are used, then idle time is reduced and readout speed improves, but hardware resources increase
Solution Approach 1:
The readout circuit is segmented into multiple independent pipeline stages (first pipeline stage with first column ADC, second pipeline stage with second column ADC). Each stage can operate independently and simultaneously, eliminating the idle time problem in serialized architectures while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
Each pipeline stage is designed as a universal module that can handle both sampling and conversion functions. This multi-functionality allows the same circuit architecture to be replicated across multiple stages without proportionally increasing overall complexity, as each stage serves multiple purposes in the data flow.
Data Source
AI summary
An image sensor includes a plurality of pixel cells organized into rows and columns of a pixel array. A bit line is coupled to each of the pixel cells within a line of the pixel array. Readout circuitry is coupled to the bit line to readout the image data from the pixel cells within the line. The readout circuitry includes a line amplifier coupled to the bit line to amplify the image data and first and second sample and convert circuits coupled in parallel to an output of the line amplifier to reciprocally and contemporaneously sample the image data and convert the image data from analog values to digital values.