SAR ADC Offset Calibration With In-Conversion Background Correction
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Solution Overview
Problem
Existing two-stage SAR ADCs require interruption of normal operation for calibration and do not account for time-varying changes due to environmental effects, limiting their performance in high-resolution applications.
Innovation Solution
A method for offset calibration in SAR ADCs that allows continuous operation by determining a calibration bit from an analog input signal, performing additional comparisons without disrupting normal operation, and adjusting variable capacitance modules to correct for offset errors, enabling background calibration and consideration of environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration processes are used in two-stage SAR ADCs, then offset errors can be corrected, but normal operation must be interrupted
Solution Approach 1:
The calibration process is performed in advance during manufacturing or initial operation, and the calibration data is stored in lookup tables. During normal operation, the pre-calibrated data is directly applied without interrupting the conversion process, thus achieving both offset error correction and continuous operation
Solution Approach 2:
Instead of performing real-time calibration on the actual ADC components, the patent creates a copy of the offset error characteristics through preliminary measurements and stores them in lookup tables. These tabulated values are then used to correct offset errors during normal operation without requiring actual calibration hardware interventions
2Measurement precision
If calibration is performed frequently to account for environmental changes, then accuracy is improved, but operational interruptions increase
Solution Approach 1:
The patent performs calibration measurements in advance under various environmental conditions and stores the results in lookup tables. When environmental changes occur, the system quickly switches to appropriate pre-calibrated data rather than performing time-consuming real-time calibration, thus maintaining accuracy while minimizing operational interruptions
Solution Approach 2:
The system performs calibration periodically during manufacturing or initialization phases, and uses these pre-acquired calibration data through lookup tables during normal operation. This periodic calibration approach allows the system to account for environmental variations without requiring continuous calibration interruptions
Data Source
AI summary
A method of offset calibration in a SAR ADC is disclosed. In one aspect, the method comprises determining a number of bits of an analog input signal (VIN), detecting if a binary code determined from the analog input signal (VIN) matches at least one trigger code, using at least one setting code to determine a calibration bit (B*LSB; B*MSB), analyzing a bit of the digital signal (COUT) and the calibration bit (B*LSB; B*MSB), determining an indication of a presence of offset error, and calibrating the offset error. As the determination of the calibration bit (B*LSB; B*MSB) requires only one additional comparison, when compared to the normal operation, the normal operation does not need to be interrupted. Therefore, the calibration can be done in the background and thus can be performed frequently thereby taking into account time-varying changes due to environmental effects.