Image Sensor Pixel Circuit With Shared Reset-Bias Readout Node
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Solution Overview
Problem
Conventional image sensors require multiple selection transistors, signal lines, and wiring for bias and reset voltages, which decreases the fill factor and leads to poor Gb/Gr balance due to occupied circuit space and spanning signal lines across the pixel array.
Innovation Solution
The image sensor integrates reset and bias voltage signal lines into a single circuit node of the column readout circuit, eliminating the need for selection transistors and metal wiring, and incorporates a pull-down transistor to achieve pixel selection, thereby enhancing fill factor and Gb/Gr balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple selection transistors, signal lines, and wiring are provided for bias and reset voltages, then the image sensor can perform reset and bias functions, but the fill factor decreases and Gb/Gr balance deteriorates
Solution Approach 1:
The patent merges the reset signal line and bias signal line into a single shared signal line that carries both reset and bias voltages. This consolidation eliminates redundant wiring and transistors, directly improving the fill factor while maintaining both reset and bias functions through time-multiplexed signal transmission.
Solution Approach 2:
The shared signal line is designed to serve multiple functions by transmitting different voltages at different time periods. During the first time period, it provides reset voltage; during the second time period, it provides bias voltage. This multi-functionality eliminates the need for separate dedicated lines for each function.
2Reliability
If multiple selection transistors and signal lines are provided, then the image sensor can provide bias voltages and reset voltages, but the circuit space is occupied and Gb/Gr balance becomes poor
Solution Approach 1:
The patent combines multiple separate circuit components (selection transistors for bias and reset, separate signal lines) into a single shared signal line structure. This merging reduces the overall circuit space occupation while maintaining the capability to provide both bias and reset voltages through temporal multiplexing.
Solution Approach 2:
The patent extracts and eliminates redundant components from the conventional design. Specifically, it removes the need for separate selection transistors and signal lines for bias and reset functions, keeping only the essential shared signal line and minimal transistor structure, thereby reducing circuit space.
3Reliability
If selection transistors are provided in the pixel array, then bias and reset functions can be performed, but the fill factor decreases
Solution Approach 1:
The patent merges the functions of multiple selection transistors into a single shared signal line structure with minimal transistor elements. This consolidation dramatically reduces the area occupied by selection transistors within the pixel array, thereby improving the fill factor while preserving the essential bias and reset functions.
Data Source
AI summary
An image sensor and an operating method thereof are provided. The image sensor includes a first pixel circuit, a first column readout circuit, and a second column readout circuit. The first pixel circuit includes a first pixel unit, a first transfer transistor, a first reset transistor, a first readout transistor, and a first capacitor. The first column readout circuit includes a first circuit node. The second column readout circuit includes a bias transistor. A first terminal of the first reset transistor and a first terminal of the first readout transistor are coupled to the first circuit node, and a second terminal of the first readout transistor is coupled to the bias transistor.