Shared Op-Amp Pixel Readout for Longer Image Sensor Exposure
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Solution Overview
Problem
Image sensors that share an operational amplifier among multiple pixel circuits face limited exposure time for each pixel circuit, restricting their ability to capture signals effectively due to the need for synchronized timing across channels.
Innovation Solution
The implementation of a readout circuit with a shared operational amplifier, switching devices, and a computation circuit that allows simultaneous exposure and reading of pixel circuits across different rows or columns, and encodes channel signals to separate and recover sensed signals from the operational amplifier's output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple channels share a same operational amplifier, then hardware cost and device size are reduced, but the exposure time for a single pixel circuit is significantly limited
Solution Approach 1:
The pixel array is divided into multiple rows or columns that can be exposed and read simultaneously through switching devices. This segmentation allows the shared operational amplifier to process multiple pixel circuits in parallel across different spatial segments, extending the effective exposure time while maintaining hardware cost efficiency.
Solution Approach 2:
The patent transitions from sequential time-based reading to simultaneous spatial-parallel reading by enabling multiple rows/columns to be exposed and read at the same time. This dimensional change from 1D temporal processing to 2D spatio-temporal processing extends exposure time without requiring additional operational amplifiers.
2Area of stationary object
If multiple channels share a same operational amplifier, then device size is reduced, but the available exposure time for reading a single pixel circuit is limited
Solution Approach 1:
Multiple pixel circuits from different rows or columns are merged into the same readout path through switching devices, allowing them to share the operational amplifier simultaneously. This merging enables parallel processing of multiple signals through a single amplifier, reducing device size while extending exposure time.
Solution Approach 2:
The operational amplifier is designed to serve multiple functions by reading from multiple rows or columns simultaneously through controlled switching. This multi-functionality allows a single amplifier to replace multiple amplifiers, reducing device size while maintaining extended exposure time through parallel operation.
3Duration of action of moving object
If simultaneous exposure and reading of multiple pixel circuits is enabled, then exposure time is extended, but signal separation and recovery becomes complex
Solution Approach 1:
Switching devices serve as intermediaries between pixel circuits and the operational amplifier, controlling which pixels are connected at each moment. This intermediary mechanism enables systematic management of simultaneous signals, allowing extended exposure time while maintaining manageable signal processing complexity through controlled connectivity.
Solution Approach 2:
The switching devices operate in periodic cycles, systematically connecting different rows or columns to the operational amplifier in a repeating pattern. This periodic action creates a structured, predictable signal mixing pattern that simplifies the recovery process through known transformation matrices, extending exposure time without excessive complexity.
Data Source
AI summary
A readout circuit for reading sensed signals of a pixel array. The readout circuit includes: an operational amplifier, a plurality of switching devices and a computation circuit. The operational amplifier is arranged to generate an output signal in each amplifier output cycle. In each amplifier output cycle, each of the switching devices is controlled by a switch controlling signal to selectively couple pixel circuits to the differential input terminals of the operational amplifier. The computation circuit is arranged to the recover a plurality of sensed signal respectively corresponding to a plurality of pixel circuits. In each amplifier output cycle, at least two of the switching devices are turned on, such that the operational amplifier receives the sensed signals of at least two pixel circuits in the pixel array simultaneously and sums the sensed signals of the at least two pixel circuits to generate the output signal.