Image Sensor Ramp Buffer Circuit for Low-Noise ADC
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Solution Overview
Problem
Image sensors face challenges in maintaining high-quality image generation while operating at low power, particularly due to noise deterioration in analog-to-digital conversion processes.
Innovation Solution
The implementation of a pixel array with a ramp signal generator, a buffer circuit featuring a super source follower structure, and an analog-to-digital conversion circuit that compares pixel signals with buffered ramp signals to generate pixel values, reducing noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional buffer structure is used in the analog-to-digital conversion circuit, then the circuit can operate, but noise is generated that deteriorates image quality
Solution Approach 1:
The patent introduces a buffer circuit as an intermediary component between the ramp signal generator and the comparator. This buffer acts as a mediator that isolates the comparator from direct connection to the ramp signal generator, thereby preventing noise generation while maintaining proper signal buffering functionality. The buffer serves as a protective intermediary that eliminates the harmful noise effect without compromising the conversion process.
2Reliability
If high power is supplied to the image sensor, then image quality can be maintained, but power consumption increases
Solution Approach 1:
The buffer circuit is designed with a self-service capability through its specific configuration that allows it to maintain proper buffering function while consuming minimal power. The circuit structure enables the buffer to automatically regulate its operation to achieve optimal performance with reduced power requirements, eliminating the need for high power supply to maintain image quality.
3Adaptability or versatility
If the buffer input range is fixed, then the circuit design is simple, but the buffer cannot adapt to different signal levels
Solution Approach 1:
The buffer circuit incorporates dynamic input range adjustment capability that allows the input range to be modified based on signal level requirements. The circuit can switch between different input range configurations (first input range and second input range) to adapt to different operating conditions. This dynamic adjustment is achieved through controlled connection of additional circuit elements that expand or contract the effective input range as needed.
Data Source
AI summary
An image sensor and an operating method of the image sensor are provided. An image sensor includes a pixel array including a plurality of pixels, a ramp signal generator configured to generate a first ramp signal, a buffer including an amplifier of a super source follower structure and outputting a second ramp signal obtained by buffering the first ramp signal, and an analog-to-digital conversion circuit configured to compare a pixel signal output from the pixel array with the second ramp signal and converting the pixel signal to a pixel value.