Image Sensor Column Readout With Shared Delta-Sigma Filters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Designing column circuitry for image sensors with hundreds or thousands of columns is challenging due to the need for multiple dedicated filtering stages, which occupies significant area on the chip.
Innovation Solution
Implementing a shared decimation filter circuit among multiple delta sigma converters, where bit streams are stored in column memory and processed in parallel, reducing the overall area required for column readout circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated filtering stages are implemented for each pixel column, then signal processing quality is maintained, but chip area occupied by column circuitry increases significantly
Solution Approach 1:
A single decimation filter circuit is designed to serve multiple pixel columns sequentially. The filter is shared among N pixel columns, where the same filtering hardware processes signals from different columns at different time periods, eliminating the need for N separate filter circuits and dramatically reducing chip area while maintaining signal processing quality
Solution Approach 2:
The system dynamically switches the filter's input source between multiple pixel columns using column selection circuitry. Instead of a static one-to-one mapping between columns and filters, the filter dynamically connects to different columns based on timing signals, enabling time-multiplexed operation that reduces hardware requirements
2Reliability
If multiple dedicated filter circuits are provided for hundreds or thousands of pixel columns, then each column's signal is processed independently, but device complexity and manufacturing cost increase
Solution Approach 1:
The signal processing function is segmented into two distinct stages: (1) parallel bit stream generation from multiple delta-sigma modulators, and (2) sequential filtering through a shared decimation filter. This segmentation allows independent processing capability to be achieved through time-multiplexing rather than spatial duplication, reducing overall system complexity
Solution Approach 2:
Column selection circuitry acts as an intermediary between the multiple pixel columns and the single shared filter. This intermediary component manages the time-multiplexed connections, routing signals from different columns to the filter at appropriate time periods, thereby enabling independent processing without requiring dedicated filter circuits for each column
3Area of stationary object
If a shared filter is used among multiple delta sigma converters, then chip area is reduced, but time is required to process bit streams from different columns sequentially
Solution Approach 1:
The shared filter operates in periodic cycles, systematically processing bit streams from different pixel columns in sequence. Each column receives a time slot for filter processing, and this periodic time-multiplexed operation allows a single filter to handle multiple columns over time, reducing area while managing processing time through structured scheduling
Solution Approach 2:
Delta-sigma modulators perform preliminary parallel processing of pixel signals, generating bit streams that are prepared for subsequent filtering. This preliminary action allows the main filtering operation to be time-multiplexed efficiently, as the preparatory work is already done in parallel before the sequential filtering stage
Data Source
AI summary
An image sensor may include an array of image pixels arranged in rows and columns. The columns of pixels are coupled to corresponding delta sigma modulators. Each group of delta sigma modulators may be coupled to a column memory circuit. The column memory circuit may receive bits serially from each pixel column in the group. Once all bits in a bit stream from each pixel column have been stored into the column memory circuit, the column memory circuit may output one bit stream at a time to a shared filter circuit. The shared filter circuit may process an entire bit stream associated with a given column in one cycle. Sharing the filter circuit among multiple pixel columns can dramatically reduce circuit area for the image sensor.