Image Sensor Readout Circuit with Digital Offset Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors experience signal distortion during analog-to-digital conversion, leading to reduced image capturing resolution due to offset values that cannot be completely eliminated by existing adder-subtracter methods.
Innovation Solution
A readout circuit with an amplifying unit, an m-bit analog-to-digital converter, and an m-to-n bit digital converting unit, which includes a programmable gain amplifier and an adder-subtracter, converts line analog image signals into m-bit and then n-bit digital signals using a k-bit control signal, allowing for precise amplitude correction and reduction of image distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an adder-subtracter is used to subtract a modifying signal from the actual image signal, then image distortion is reduced, but the capturing resolution remains relatively low because the modifying signal cannot completely eliminate the offset value
Solution Approach 1:
The patent segments the analog-to-digital conversion process into two distinct stages: first an m-bit ADC converts the analog signal to digital, then a digital offset correction unit subtracts the offset value from the digital signal. This segmentation allows precise offset elimination in the digital domain without the resolution limitations of analog subtraction, thereby resolving the contradiction between distortion reduction and resolution maintenance.
Solution Approach 2:
The patent introduces a digital offset value as an intermediary element that mediates between the analog signal and the final digital output. By converting the offset correction to the digital domain, the system achieves precise offset elimination without introducing additional distortion, thus improving both distortion reduction and capturing resolution simultaneously.
2Measurement precision
If the modifying signal has higher resolution than the analog-to-digital converter, then offset correction is attempted, but the signal distortion cannot be completely eliminated resulting in low capturing resolution
Solution Approach 1:
The patent inverts the traditional approach by performing offset correction in the digital domain rather than the analog domain. Instead of subtracting an analog modifying signal from the analog image signal, the system converts the analog signal to digital first, then subtracts the digital offset value. This inversion eliminates the resolution mismatch problem and achieves complete offset elimination, resolving the contradiction between correction precision and capturing resolution.
Data Source
AI summary
A readout circuit is adapted for receiving a line analog image signal from an image sensor array of an image sensor. The readout circuit includes an amplifying unit, an m-bit analog-to-digital converter, and an m-to-n bit digital converting unit. The amplifying unit is adapted for amplifying and correcting amplitude of the line analog image signal, and outputs an amplified and corrected analog signal. The m-bit analog-to-digital converter is coupled to the amplifying unit, and is operable to convert the amplified and corrected analog signal into a corresponding m-bit digital signal. The m-to-n bit digital converting unit is coupled to the m-bit analog-to-digital converter, receives the m-bit digital signal from the m-bit analog-to-digital converter, and is responsive to a k-bit control signal for converting the m-bit digital signal into an n-bit digital signal, wherein m is greater than or equal to n.