Low-Noise Image Sensor Pixel With Capacitive Reset Correction
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Solution Overview
Problem
Existing image sensor pixel circuits face challenges in reducing thermal noise during the reset operation, which degrades the sensitivity and signal-to-noise ratio, and current solutions like correlated double sampling either prolong read operations or require additional memory or complex pixel architectures.
Innovation Solution
A pixel circuit with a reset voltage correction circuit that includes a capacitance coupling mechanism between the sense node and a correction node, using switches to selectively apply the reset voltage, allowing for the suppression of thermal noise without the need for additional memory or complex pixel structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If correlated double sampling technique is used to reduce thermal noise, then thermal noise is reduced, but read operation time is extended or additional memory is required
Solution Approach 1:
The patent applies preliminary action by pre-charging the sense node to a corrected reset voltage level that has already had the thermal noise component removed through the correction circuit involving the first and second transistors. This preliminary correction of the reset voltage level eliminates the need for post-sampling noise reduction techniques like correlated double sampling, thereby reducing thermal noise without extending read operation time
2Object-affected harmful factors
If correlated double sampling technique is used to reduce thermal noise, then thermal noise is reduced, but device complexity is increased due to memory capacitor array or additional transistors
Solution Approach 1:
The patent merges the reset voltage correction function directly into the pixel circuit by integrating the correction circuit with the sense node. The first transistor couples the sense node to a correction node, and the second transistor couples the correction node to the reset voltage, creating a compact structure that corrects thermal noise without requiring separate memory capacitor arrays or additional complex pixel architectures like the 4T pinned photodiode structure
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
The proposed solution effectively reduces thermal noise within the pixel circuit, improving the sensitivity and signal-to-noise ratio without extending read operations or adding complexity, thus providing a compact and efficient noise correction method.
Implementation Method 1
a correction node coupled by a capacitance to the sense node
Data Source
AI summary
A pixel circuit comprising: a light-sensing element; a first transistor having its control node coupled to a sense node and its source coupled to a readout path of the pixel circuit; and a reset voltage correction circuit comprising: a first switch configured to selectively couple an input node of the reset voltage correction circuit to a correction node, the input node being connected to the sense node or to the source of the first transistor, the correction node being coupled by a capacitance to the sense node; and a second switch configured to selectively couple the correction node to a reset voltage.