Multi-Comparator SAR ADC Offset Calibration for Better Linearity
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Solution Overview
Problem
Successive approximation register (SAR) analog-to-digital converters (ADCs) experience non-linear distortion due to comparator offset mismatches, leading to statistical imbalances in bit distributions, which affect the accuracy of analog-to-digital conversion.
Innovation Solution
The implementation of multiple comparators operating in staggered phases, with a distribution calculation module that adjusts the offset of the least-significant bit comparator to achieve equal distributions of 1's and 0's, thereby reducing differential offset and eliminating the need for dedicated offset correction cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If multiple comparators are used to speed up the comparison process, then conversion speed is improved, but non-linear distortion increases due to comparator offset mismatches
Solution Approach 1:
The patent implements a feedback mechanism where the digital output is fed back through a digital-to-analog converter (DAC) to the comparator input. This feedback loop allows the system to automatically adjust and equalize the offset voltages of multiple comparators by comparing the reconstructed analog signal with the original input, thereby correcting non-linear distortion while maintaining high conversion speed
Solution Approach 2:
The patent replaces traditional analog offset correction circuits with a digital processing approach. By using digital logic to calculate offset corrections based on statistical analysis of comparator outputs and applying corrections through digital control of the DAC, the system eliminates the need for complex analog correction mechanisms while maintaining linearity
2Measurement precision
If dedicated offset correction cycles are implemented, then measurement precision is improved, but productivity decreases due to additional correction time
Solution Approach 1:
The patent enables continuous offset correction by integrating the correction process into the normal conversion operation. The feedback mechanism operates continuously alongside regular conversions, allowing offset equalization to occur without interrupting the conversion stream, thus maintaining both high precision and productivity
Solution Approach 2:
The system performs self-correction of comparator offsets using its own operational data. By analyzing the statistical distribution of comparator outputs during normal operation and automatically adjusting offsets through the feedback loop, the ADC corrects its own errors without requiring external calibration equipment or dedicated correction cycles
Data Source
AI summary
Disclosed is a successive approximation register (SAR) analog to digital converter (ADC) that uses two or more comparators. This allows the output of one comparator to be latched while the other comparators are comparing and switching. Statistical measures are used to correct the offsets of one or more of the comparators. If a statistically significant mismatch in the number of 1's and 0's occurs in a subset of the bits, adjustments to the offsets of one or more of the comparators are made until there is roughly an equal number of 1 and 0 values. This can reduce or eliminate the need for dedicated offset correction cycles.