Analog-to-digital converter charge pumping
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Solution Overview
Problem
Existing analog-to-digital conversion methods in imaging systems face challenges with conversion time and accuracy, particularly when increasing the number of bits required for precision, and are affected by the distribution of global ramp voltage signals, leading to inconsistencies across columns.
Innovation Solution
A local charge pumping method is employed, where a main capacitive element's voltage is set based on the analog voltage, and charge packets are sequentially injected or removed to compare against a reference voltage, allowing for multi-slope conversion without relying on global ramp voltage distribution, enabling more precise control over charge magnitude and timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global ramp voltage signal is distributed to ADCs of each column, then the conversion process can be performed, but different columns experience different ramp voltage signals due to electrical length and electromagnetic coupling effects
Solution Approach 1:
The patent divides the ADC system into independent column-based units, where each column has its own local DAC and capacitor array instead of sharing a global ramp voltage distribution network. This segmentation eliminates the problems of electrical length variations and electromagnetic coupling between columns, ensuring each ADC operates with its own clean, consistent voltage references.
Solution Approach 2:
Each column is equipped with local voltage generation and storage components (DAC and capacitors) rather than relying on a centralized global ramp signal. This local quality approach ensures that each column experiences identical, controlled voltage conditions independent of other columns, resolving the inconsistency caused by distribution network effects.
2Measurement precision
If multi-slope ADC with two consecutive ramp voltage signals is used to determine more bits, then the accuracy increases, but the conversion time doubles
Solution Approach 1:
The patent pre-charges capacitors in the column-based ADC to known voltage levels before conversion begins. This preliminary action allows the conversion process to proceed more efficiently by avoiding the need for sequential multi-slope ramp operations, thereby reducing conversion time while maintaining accuracy through the parallel capacitor comparison architecture.
Solution Approach 2:
The system dynamically selects and switches between different capacitor combinations in each column based on the conversion progress, enabling faster determination of digital bits compared to fixed multi-slope approaches. The dynamic reconfiguration of capacitor networks allows for accelerated conversion without sacrificing precision.
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 reduces conversion time and improves accuracy by allowing independent control of charge packets, reducing noise contributions and enabling efficient conversion of analog signals into digital numbers with enhanced precision.
Implementation Method 1
setting a voltage over a main capacitive element in dependence of the analog voltage
Implementation Method 2
Each charge pumping step comprises performing at least sub-step II of the loop comprising the sub-steps of I) injecting or removing an amount of charge into or from the main capacitive element
Implementation Method 3
comparing the voltage over the main capacitive element to a reference voltage, and, based on said comparison, either returning to sub-step I) to further change the voltage over the main capacitive element
Data Source
AI summary
The present invention relates to a converting device for converting an analog voltage into a digital number and to an imaging system comprising the same. The invention further relates to a method for converting an analog voltage into a digital number.According to the invention, one or more charge pumping steps are performed that change a voltage over a capacitive element that has been set in dependence of the voltage to be converted. During each charge pumping step, one or more substantially identical charge packets may be transferred to of from the capacitive element. The magnitude of the charge packets belonging to different charge pumping steps may be different allowing multi-slope operation.The digital number representing the analog voltage is calculated based on the net charge that has been injected into or removed from the main capacitive element as a result of having performed the one or more charge pumping steps.