Image Sensor AD Converter with Switchable Slope Voltage Modes
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Solution Overview
Problem
Current CMOS image sensors face challenges in achieving high-speed readout while maintaining image quality, particularly under conditions of long exposure or high temperature, where dark current generation degrades image quality and requires longer AD conversion times.
Innovation Solution
The image sensing device employs a dual AD conversion mode system, switching between multi-slope and single-slope modes based on imaging conditions, using a slope voltage with a temporally variable potential to optimize AD conversion speed and resolution, and adjusts the slope voltage selection according to the amount of dark current to balance readout speed and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single slope method is used for AD conversion to achieve high bit resolution signal output, then the counting time of the counter increases and readout speed decreases, but image quality is improved through higher resolution
Solution Approach 1:
The patent applies dynamics by making the slope voltage inclination adjustable rather than fixed. The AD conversion circuit dynamically changes the slope voltage inclination based on signal amplitude detection: using smaller inclination for low-amplitude signals to achieve high resolution, and larger inclination for high-amplitude signals to achieve fast readout. This resolves the contradiction by making the system adaptive to different operating conditions.
Solution Approach 2:
The patent changes the parameter of slope voltage inclination based on signal characteristics. By detecting signal amplitude and selecting appropriate slope voltages with different inclinations, the system optimizes the trade-off between resolution and speed. This parameter change approach allows the same hardware to achieve both high resolution and fast readout under different conditions.
2Productivity
If low bit resolution ADC is used to achieve high speed readout, then readout speed is improved, but image quality deteriorates under imaging conditions with large dark current
Solution Approach 1:
The patent implements feedback by detecting the signal amplitude and using this information to select the appropriate slope voltage inclination. The system continuously monitors signal characteristics and adjusts the AD conversion parameters accordingly. This feedback mechanism ensures that even when dark current is present, the system can detect the actual signal level and choose the appropriate resolution mode, preventing image quality deterioration.
Solution Approach 2:
The system changes the AD conversion parameter (slope voltage inclination) based on detected signal amplitude. When dark current causes large amplitude signals, the system detects this and selects slope voltages with larger inclination for fast readout. When actual optical signals are small, the system uses smaller inclination for high resolution. This dynamic parameter adjustment resolves the contradiction between speed and quality in the presence of dark current.
3Quantity of substance
If exposure time is increased to capture more light, then signal amplitude increases, but dark current generation increases and requires longer AD conversion time
Solution Approach 1:
The patent changes the slope voltage inclination parameter based on signal amplitude caused by exposure conditions. For large amplitude signals from long exposure, the system selects slope voltages with larger inclination, which reduces the counting time required for AD conversion. This dynamically adapts the conversion time to the actual signal level, preventing unnecessary time loss even when signal amplitude is large due to extended exposure.
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 approach enables high-speed readout while maintaining high image quality by adapting AD conversion modes to imaging conditions, effectively mitigating the impact of dark current and achieving efficient digital signal processing.
Implementation Method 1
a photoelectric conversion portion that converts incident light into electrical charge
Data Source
AI summary
An image sensing device includes: a plurality of pixels; and an AD converter that compares a pixel signal output from the plurality of pixels with a slope voltage having a temporally variable potential so as to perform AD conversion on the pixel signal, and switching is performed between a first mode and a second mode according to an imaging condition, the first mode being a mode in which the pixel signal is AD converted by selecting one from among a plurality of slope voltages and comparing the pixel signal with the selected slope voltage, and the second mode being a mode in which the pixel signal is AD converted by comparing the pixel signal with a predetermined slope voltage.