ADC Background Calibration for Offset, Gain, and Nonlinearity
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Solution Overview
Problem
Conventional analog-to-digital converters (ADCs) face challenges with offset, gain, and non-linearity errors, which are exacerbated by temperature variations and require calibration methods that interrupt data acquisition and reduce data rate, failing to effectively address higher-order non-linearity errors.
Innovation Solution
A background calibration method for ADCs that estimates offset, gain, and non-linearity errors without interrupting ADC operation, using techniques such as reversing input signal polarity and modifying input samples to calculate correction factors, allowing continuous data acquisition and accurate error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration techniques are used to correct offset and gain errors, then measurement precision is improved, but productivity deteriorates due to data rate reduction up to a factor of 6
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing calibration lookup tables (LUTs) containing correction factors for offset, gain, and non-linearity errors during manufacturing or initialization. During operation, the system performs background calibration by comparing actual converter outputs with expected values from the LUTs and applies corrections without interrupting data acquisition, thus maintaining high productivity while improving measurement precision.
Solution Approach 2:
The patent implements continuity of useful action through background calibration techniques that continuously correct ADC errors during normal operation. The calibration process runs in parallel with data acquisition using unused bits or redundant resources, ensuring that measurement precision is maintained without interrupting the productive data collection process, thereby preserving both accuracy and productivity.
2Measurement precision
If conventional calibration techniques are used to correct offset and gain errors, then measurement precision is improved, but device complexity increases due to additional calibration circuits and procedures
Solution Approach 1:
The patent applies self-service by implementing background calibration algorithms that automatically detect and correct offset, gain, and non-linearity errors using the converter's own resources during normal operation. The system uses its existing digital signal processing capabilities and unused bits to perform self-calibration without requiring external calibration equipment or complex additional hardware circuits, thus improving measurement precision while minimizing device complexity.
Solution Approach 2:
The patent implements universality by designing a calibration system that handles multiple error types (offset, gain, and non-linearity errors) using a unified background calibration approach. The same calibration infrastructure and algorithms are used to correct various error sources simultaneously, reducing the need for separate dedicated circuits for each error type and thereby improving measurement precision without proportionally increasing device complexity.
3Measurement precision
If conventional calibration techniques are used, then offset and gain errors are corrected, but higher order non-linearity errors remain uncorrected
Solution Approach 1:
The patent applies segmentation by dividing the error correction process into distinct components: offset correction, gain correction, and non-linearity correction. Each error type is addressed separately through dedicated calibration algorithms and lookup tables, allowing the system to comprehensively correct multiple error sources including higher-order non-linearities that conventional single-stage calibration methods miss, thereby improving both measurement precision and correction completeness.
Solution Approach 2:
The patent implements partial or excessive action by applying correction factors for offset, gain, and non-linearity errors even when only offset and gain correction might be minimally sufficient. The background calibration system calculates and applies comprehensive corrections including higher-order non-linearity terms, ensuring that measurement precision is maximized and all significant error sources are addressed, providing robust error correction coverage.
Data Source
AI summary
A method for calibrating an analog-to-digital converter includes sampling an analog input signal and generating input samples, reversing the polarity of at least one input sample, averaging the digital output codes associated with a first pair of input samples where the first pair of input samples has opposite polarities, and generating an offset correction value being the average of the digital output codes associated with the first pair of input samples. In another embodiment, a method for calibrating an ADC includes sampling the analog input signal and generating input samples, introducing an incremental value to modify the magnitude of at least one input sample, computing an actual gain value using the digital output codes associated with a first input sample and a second input sample having the modified magnitude, and generating a gain correction value being the ratio of an ideal gain of the ADC to the actual gain.