SAR ADC Capacitor Array Calibration for Capacitance Deviation
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Solution Overview
Problem
SAR ADCs face output errors due to deviations in capacitor array capacitance during the manufacturing process, leading to inaccurate signal sampling and approximation.
Innovation Solution
A calibration method and system that calculates average code densities for digital code groups, compares them to predetermined densities, and adjusts the capacitance of under-correction capacitor elements in the capacitor array to correct deviations, ensuring precise capacitance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance of capacitor array is designed precisely according to powers of 2, then SAR ADC can achieve accurate signal sampling and approximation, but manufacturing process variations cause capacitance deviations leading to erroneous output results
Solution Approach 1:
The patent applies preliminary action by performing calibration operations before the SAR ADC is put into normal use. The calibration process pre-adjusts the capacitance values of capacitor elements based on their actual measured values, storing correction data that will be used during operation. This preliminary calibration compensates for manufacturing variations before they affect output accuracy.
Solution Approach 2:
The patent changes the capacitance parameters of capacitor elements dynamically during calibration. By measuring actual capacitance values and comparing them to ideal values, the system adjusts the effective capacitance through switching configurations or trimming mechanisms, transforming the fixed manufacturing-defected parameters into corrected operational parameters that restore the required powers of 2 relationships.
2Measurement precision
If capacitance deviation occurs during manufacturing, then SAR ADC produces erroneous output results, but adding calibration circuits and procedures increases device complexity
Solution Approach 1:
The patent implements self-service by enabling the SAR ADC to perform its own calibration using built-in test resources. The calibration process utilizes the existing capacitor array, comparators, and control logic to measure and adjust its own capacitance values without requiring external calibration equipment. This self-calibration capability reduces the need for complex external calibration systems while maintaining output accuracy.
Solution Approach 2:
The patent employs feedback mechanisms where the actual output codes from the SAR ADC are monitored and fed back to the calibration controller. The system compares measured code densities against expected densities and uses this feedback information to iteratively adjust capacitor switching configurations or trimming elements, creating a closed-loop calibration process that automatically corrects manufacturing deviations.
3Measurement precision
If capacitor array capacitance deviates from design values, then signal sampling and approximation become inaccurate, but real-time calibration reduces errors caused by manufacturing variations
Solution Approach 1:
The patent performs calibration operations during the manufacturing test phase or initial startup period, before the SAR ADC enters its normal operational phase. By completing the capacitance measurement and adjustment procedures in advance, the system eliminates the need for time-consuming calibration during actual signal processing operations, thus recovering lost time while maintaining sampling accuracy.
Solution Approach 2:
The patent implements calibration as a periodic maintenance operation rather than a continuous process. The system schedules calibration events at predetermined intervals or under specific conditions (such as temperature changes or drift detection), allowing the SAR ADC to operate at full capacity between calibration events. This periodic approach minimizes the impact on overall productivity while ensuring accuracy is maintained.
Data Source
AI summary
A calibration method applicable for a SAR ADC comprising a capacitor array, comprises the following operations: Inputting an input signal to the SAR ADC, wherein the SAR ADC is configured to generate an output signal according to the input signal, and the output signal comprises multiple selected digital codes; calculating average code densities for multiple digital code groups, respectively, wherein the multiple digital code groups are determined by dividing the multiple selected digital codes, and each of the multiple digital code groups comprises one or more selected digital codes of the multiple selected digital codes; calibrating capacitance of a first under-correction capacitor element of the capacitor array according to the first comparison result.