Flash ADC Residue Ladder Switching to Cut Parasitic Capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Flash analog-to-digital converters face complexity and increased parasitic capacitance due to the large number of switches and wires required for reference ladders, especially in multi-stage designs, which hinders high-speed conversion and increases silicon area and power dissipation.
Innovation Solution
The solution involves reducing the number of switches by using a dual residue differential converter architecture, where each selector for one residue signal selects voltages from one half of the ladder and employs crossover switches to reverse output signals at the coarse quantization's center value, effectively reducing the total number of switches from 32 to 24 for 3-bit coarse quantization, and further to 68 for 5-bit coarse quantization, thereby minimizing capacitive load and wire count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multi-stage flash converter uses a large number of switches and wires for reference ladder connections to perform digital to analog conversion, then the conversion resolution and accuracy are improved, but the device complexity and parasitic capacitance increase significantly
Solution Approach 1:
The patent divides the reference ladder into multiple segments or groups, and uses a hierarchical selection mechanism where coarse quantization selects a group and fine quantization selects within the group. This segmentation reduces the number of switches needed in each stage while maintaining the overall resolution capability.
Solution Approach 2:
The patent introduces a hierarchical dimension to the switch selection process by implementing multiple stages of quantization (coarse and fine). Instead of a single large switch matrix, the system uses sequential selection across different dimensional levels, reducing the peak number of switches required at any one time.
2Measurement precision
If a multi-stage flash converter uses a large number of switches for reference ladder connections to achieve required resolution, then the conversion accuracy is improved, but the parasitic capacitance increases which hinders high-speed conversion
Solution Approach 1:
By segmenting the quantization process into coarse and fine stages with corresponding switch groups, the patent reduces the capacitive load on the reference ladder at any given moment. This segmentation allows faster switching operations while maintaining the cumulative resolution accuracy of all stages combined.
Solution Approach 2:
The patent implements a dynamic, sequential switching strategy where switches are activated in stages rather than simultaneously. The coarse quantization switches operate first, followed by fine quantization switches, creating a time-multiplexed operation that reduces instantaneous capacitive burden and enables higher conversion speeds.
3Adaptability or versatility
If a multi-stage flash converter uses a large number of switches and wires to perform digital to analog conversion, then the conversion functionality is improved, but the silicon area increases
Solution Approach 1:
The patent segments the converter into multiple functional stages (coarse quantization, fine quantization, residue generation) with dedicated switch groups for each stage. This modular segmentation allows efficient use of silicon area by reusing reference ladder resources across stages and reducing the total switch count compared to a single-stage implementation with equivalent resolution.
Solution Approach 2:
The reference ladder serves multiple functions: it provides reference voltages for coarse quantization comparators, fine quantization comparators, and digital-to-analog conversion in both stages. This multi-functionality reduces the need for separate reference structures, thereby reducing overall silicon area while maintaining full conversion functionality.
4Measurement precision
If a multi-stage flash converter uses a large number of switches for reference ladder connections to achieve required resolution, then the conversion precision is improved, but the power dissipation increases
Solution Approach 1:
The patent implements dynamic, time-multiplexed operation where switch groups are activated sequentially in coarse and fine stages rather than simultaneously. This dynamic operation reduces the instantaneous power consumption and total energy dissipation while maintaining the cumulative precision benefits of multiple quantization stages.
Solution Approach 2:
By segmenting the conversion process into distinct stages with dedicated switch groups, the patent enables efficient power management where only the necessary switch groups are active at each moment. This segmentation reduces total power dissipation compared to a single-stage design requiring all switches to be simultaneously operational for equivalent precision.
Data Source
AI summary
A flash analog-to-digital converter comprising a resistive reference ladder, a set of comparators for comparing the analog input signal with the reference voltages of the ladder to provide a digital code representing a coarse quantization of the input signal, a set of switches connected to the reference ladder and controlled by said digital code to provide an analog representation of the coarse quantization of the input signal, means to derive from said analog representation of the coarse quantization and from the input signal one or more residue signals and a fine analog-to-digital converter stage to generate a digital code representing a fine quantization of the one or more residue signals. For minimizing the number of switches required, each selector for one residue signal selects voltages of one half of the ladder at two values of the coarse quantization and the output signals of the two selectors for that residue signal are reversed by a crossover switch when the coarse quantization passes its center value.