Ramp Signal Offset Control for Low-Noise CMOS Image Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Noise generated by the ramp signal generator in CMOS image sensors impacts the image quality of CMOS image sensors, which is a limitation in achieving high-quality image capture.
Innovation Solution
A ramp signal generator is designed with a reference voltage generator, gain controller, ramp signal controller, and offset controller to precisely adjust the offset of the ramp signal, minimizing noise by forming a current mirror and responding to control signals, thereby improving the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a ramp signal generator is used in the ADC circuit, then the analog-to-digital conversion can be performed, but noise is generated that impacts image quality
Solution Approach 1:
The ramp signal generator is divided into multiple independent control modules: a reference voltage generator, a gain controller, and an offset controller. Each module independently controls specific parameters of the ramp signal, allowing precise adjustment of the signal characteristics while minimizing noise generation during the analog-to-digital conversion process.
2Object-generated harmful factors
If the offset of the ramp signal is not precisely controlled, then the circuit operation is simple, but quantization noise increases and image quality deteriorates
Solution Approach 1:
The offset controller receives feedback regarding the ramp signal characteristics and dynamically adjusts the offset voltage to optimize the signal distribution. This feedback mechanism enables precise control of the ramp signal offset, reducing quantization noise while maintaining a manageable circuit structure through intelligent control rather than complex hardware.
3Measurement precision
If correlated double sampling is performed, then the signal to noise ratio is improved, but noise from the ramp signal generator still impacts image quality
Solution Approach 1:
The gain controller dynamically adjusts the gain parameter of the reference voltage based on signal conditions, while the offset controller modifies the offset parameter of the ramp signal. These parameter changes optimize the correlation double sampling process by ensuring the ramp signal accurately matches the pixel signal characteristics, thereby improving signal-to-noise ratio while minimizing the transmission of generator noise to the ADC.
Data Source
AI summary
Disclosed are devices, systems and methods for allowing a ramp signal generator to reduce noise. A ramp signal generator may include a reference voltage generator configured to generate a reference voltage, a gain controller configured to control a gain of the reference voltage, a ramp signal controller configured to generate a ramp signal in response to an output signal of the gain controller, and an offset controller coupled to an output terminal of the gain controller in the form of a current mirror, and control an offset of the ramp signal in response to a control signal.