SAR ADC Thermometer Coding to Reduce Integral Nonlinearity
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Solution Overview
Problem
Existing successive approximation AD converters require calibration to address integral nonlinear errors due to element mismatch in DA converters, which increases circuit area and costs.
Innovation Solution
A successive approximation AD converter design that includes a comparator, successive approximation register, thermometer decoder, and average value calculator, which switches thermometer code conversion rules to generate AD conversion values without the need for calibration, thereby improving integral nonlinear error without element mismatch calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If calibration is performed to correct integral nonlinear error, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The DA converter is divided into multiple DA conversion elements (first through fourth elements) with different bit weights. By segmenting the converter and applying different thermometer code conversion rules to different elements, the patent achieves error reduction without requiring full calibration of the entire system.
Solution Approach 2:
The patent changes the thermometer code conversion rules applied to different DA conversion elements. Specifically, different elements use different conversion rules (e.g., first rule for first element, second rule for second element), which transforms the error characteristics and reduces integral nonlinear error without calibration.
2Manufacturing precision
If multiple DA conversion elements are used, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Different DA conversion elements are assigned different local properties in the form of different thermometer code conversion rules. The first DA conversion element uses a first conversion rule while the second element uses a second conversion rule, creating local quality variations that reduce differential nonlinear error.
Solution Approach 2:
The patent introduces asymmetry by applying different conversion rules to different DA conversion elements rather than using a uniform rule. This asymmetric approach balances the error contributions from multiple elements, reducing the overall differential nonlinear error.
Data Source
AI summary
A successive approximation ADC includes: a comparator generating a judge signal related to an input analog and a reference signals; a SAR successively generating a register signal including a first and a second bit signals based on the judge signal and generating an AD conversion value of the input analog signal; a thermometer decoder switching different thermometer code conversion rules and converting the first bit signal to thermometer codes corresponding to the different thermometer code conversion rules in one AD conversion cycle; a first and a second DA converters respectively converting the thermometer codes to a first analog signal and the second bit signal to a second analog signal; an average value calculator averaging the AD conversion values by the thermometer codes. Two of the different thermometer codes have values that a high-order bit and a low-order bit groups by dividing total bits of the thermometer code equally are exchanged.