CMOS Image Sensor Signal Processing Circuit for Fixed-Pattern Noise Reduction
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in maintaining image quality due to fixed-pattern noise caused by threshold variations among MOSFETs, particularly when applying noise cancellation methods to image sensing devices with configurations other than one amplifier per pixel column, which increases complexity and cost.
Innovation Solution
A signal processing device with a connection control unit that manages the connection between a comparing unit and a floating diffusion in CMOS image sensors, using a MOSFET as a switch to connect or disconnect the output of the comparing unit to the floating diffusion based on a control signal, allowing for feedback of the reset level and maintaining it, thereby inhibiting threshold variations across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If one amplifier is arranged for one pixel column to implement negative feedback noise cancellation, then fixed-pattern noise is reduced, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple pixel columns into groups that share a single amplifier. Specifically, multiple pixel columns are combined into a first group sharing a first amplifier and a second group sharing a second amplifier, reducing the total number of amplifiers required while maintaining noise cancellation functionality through the sharing mechanism
Solution Approach 2:
The shared amplifiers serve multiple functions by handling reset operations and signal amplification for multiple pixel columns simultaneously. The first amplifier serves both as a reset amplifier for the first group of pixel columns and as a signal amplifier, while the second amplifier similarly serves dual functions for the second group
2Measurement precision
If conventional negative feedback method is applied to devices with shared amplifiers, then noise cancellation is achieved, but it becomes difficult to apply to image sensing devices with configurations other than one amplifier per pixel column
Solution Approach 1:
The patent implements dynamic control of the shared amplifiers through sequentially different reset control signals. The first amplifier receives a first reset control signal and the second amplifier receives a second reset control signal, allowing flexible adaptation to different pixel column groupings and configurations while maintaining effective noise cancellation
Solution Approach 2:
The pixel array is segmented into multiple groups of pixel columns, where each group is assigned to a specific amplifier. This segmentation allows the system to scale and adapt to different device configurations by adjusting the grouping strategy without requiring a complete redesign of the feedback mechanism
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
This solution effectively inhibits deterioration in image quality by allowing each pixel to maintain a consistent reset level, reducing noise and improving image capture quality even in devices with shared reset control signals, while minimizing circuit complexity and cost.
Implementation Method 1
a connection unit which connects or disconnects the output of the comparing unit to or from the floating diffusion of the unit pixel according to control of the connection control unit. The connection unit may include a MOSFET which drives as a switch to connect or disconnect the output of the comparing unit to or from the floating diffusion of the unit pixel on the basis of a control signal supplied from the connection control unit
Data Source
AI summary
The present technology relates to a signal processing device, a controlling method, an image sensing device, and an electronic device capable of inhibiting deterioration in image quality of a captured image.The signal processing device of the present technology connects an output of a comparing unit which compares a signal read from a unit pixel with reference voltage to a floating diffusion of the unit pixel, thereby feeding back the output of the comparing unit to the floating diffusion as a reset level, and disconnects the output of the comparing unit from the floating diffusion of the unit pixel, thereby allowing the floating diffusion to maintain the reset level. The present technology may be applied to the image sensing device and the electronic device, for example.