Comparator Circuit Topology for Low-Noise Image Sensor ADCs
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Solution Overview
Problem
Existing analog-digital converting circuits in CMOS image sensors suffer from high noise levels, which degrade image quality, particularly in low-illumination environments.
Innovation Solution
The implementation of a comparator with a specific transistor configuration, including P-type and N-type transistors, reduces noise by eliminating current mirror structures and incorporating transistors connected to ground or power supply voltage, coupled with a counter to enhance noise reduction and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional comparator structure with current mirror is used, then the circuit can perform analog-to-digital conversion, but the noise level increases degrading image quality
Solution Approach 1:
The patent removes the current mirror structure from the comparator circuit, extracting the noise-generating component while preserving the essential comparison function through an alternative transistor configuration that eliminates the harmful current mirroring effect
Solution Approach 2:
The patent changes the electrical parameters and configuration of the comparator by using a specific transistor arrangement with controlled connections to ground and power supply, altering the noise characteristics while maintaining conversion functionality
2Object-generated harmful factors
If noise reduction measures are implemented in the comparator, then image quality improves, but the device complexity increases
Solution Approach 1:
The patent applies noise reduction locally within the comparator circuit by strategically connecting specific transistors to ground or power supply at critical nodes, reducing noise without requiring comprehensive circuit redesign
Solution Approach 2:
The comparator circuit achieves noise reduction through its own internal transistor configuration and grounding strategy, making the noise reduction function inherent to the circuit operation rather than requiring external noise filtering components
Data Source
AI summary
Provided are analog-digital converting circuits including a comparator, and an image sensor. The analog-digital converting circuit include a counter and a comparator, the comparator including a first P-type transistor including a gate connected to a first input node of the comparator, a second P-type transistor including a gate connected to a second input node of the comparator, a first N-type transistor including a gate connected to the first input node and a drain connected to the first P-type transistor, a second N-type transistor including a gate connected to the second input node and a drain connected to the second P-type transistor, and a transistor including a gate connected to the drain of the first N-type transistor and a source to which ground voltage or power supply voltage is applied.