Image Sensor Counter Grouping for Supply Crosstalk Reduction
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Solution Overview
Problem
Image sensor systems face issues with current fluctuations during the counting process, leading to supply crosstalk and image quality degradation due to large peak currents and variations in bit transitions, which are exacerbated by the use of binary ripple counters and cannot be effectively addressed by gray-code counters in sensors requiring small pixel pitch.
Innovation Solution
The system groups pixel columns into groups of at least three, resetting binary counters to different initial values to reduce the variation in the number of toggling bits per counting step, and uses a toggling unit to mimic the average number of toggling bits, thereby minimizing current fluctuations. Additionally, a dummy load is employed to stabilize current during transitions between counting and non-counting modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If binary ripple counters are used for converting pixel signals to digital numbers, then the device complexity is reduced and counter footprint is minimized, but current fluctuations occur during counting due to varying bit transitions, causing supply crosstalk and image quality degradation
Solution Approach 1:
Multiple pixel columns are grouped together to share a single binary counter resource. The counter is time-multiplexed across multiple columns, reducing the total number of counters needed while maintaining the simplicity of binary ripple counter design. This merging approach minimizes device complexity and counter footprint while the grouping strategy helps average out current fluctuations.
Solution Approach 2:
The system employs periodic resetting of the binary counter to different initial values for different pixel columns. This periodic action distributes the bit transition patterns across time, preventing sustained large current draws and reducing supply crosstalk effects while maintaining the simplicity of binary counting.
2Object-affected harmful factors
If gray-code counters are used to reduce current fluctuations, then supply crosstalk is minimized, but the device complexity and counter footprint increase, making them unsuitable for sensors requiring small pixel pitch
Solution Approach 1:
The system segments pixel columns into groups that share counters, and within each group applies different initial reset values to distribute bit transition patterns. This segmentation strategy reduces the need for complex gray-code counters by using simpler binary counters with varied initialization, achieving current fluctuation reduction without increasing counter footprint.
Solution Approach 2:
The system changes the initial value parameter of the binary counter for different pixel column groups. By varying the starting point of the counting sequence across different columns, the bit transition patterns are distributed over time, reducing peak current fluctuations without requiring the structural complexity of gray-code counters.
3Measurement precision
If multiple binary counters are separately arranged for each pixel column, then conversion precision is maintained, but the device complexity and area occupied by counters increase
Solution Approach 1:
Multiple pixel columns are merged to share a single binary counter through time-multiplexed operation. Each column receives dedicated counter service in sequence, maintaining full conversion precision for each column while reducing the total counter area by a factor equal to the number of columns sharing each counter.
Solution Approach 2:
The binary counter is designed to serve multiple pixel columns universally through time-multiplexed operation. A single counter unit performs the conversion function for multiple columns sequentially, making the counter resource multi-functional and significantly reducing the total area required compared to having dedicated counters for each column.
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 significantly reduces current fluctuations, minimizing supply crosstalk and maintaining image quality by averaging bit transitions across multiple pixel columns and stabilizing current during mode transitions, while allowing for a compact counter footprint.
Implementation Method 1
a binary counter (6) configured to increase a binary count value in dependence of a clock signal and a result of said comparing
Implementation Method 2
a comparator (5) configured to compare the relevant pixel signal to the ramp signal
Implementation Method 3
The global ramp unit (4) generates a ramp voltage and provides this voltage to comparator (5)
Data Source
AI summary
The present invention relates to an image sensor system. The invention further relates to an X-ray imaging system comprising such an image sensor system. More in particular, the present invention is related to image sensor systems that use a relatively small pixel width.The present invention proposes to group the pixel columns in a plurality of column groups, each column group comprising at least three columns of pixels. The binary counters corresponding to the columns in a column group are reset at the start of a conversion cycle such that at least three columns among the at least three columns in a column group are reset to a different initial value.