SAR ADC Capacitor Segmentation for Feasible Bit-Weight Calibration
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Solution Overview
Problem
Existing successive approximation register (SAR) analog to digital converters (ADCs) face inefficiencies in calibration due to manufacturing defects and variations, leading to excess resource usage and decreased signal-to-noise ratio, as they require additional capacitors and circuitry to account for deviations, which increases power consumption and space requirements.
Innovation Solution
The solution involves replacing uncalibrated converter elements with pairs of smaller elements, each calibrated independently by switching them between a reference voltage and ground, ensuring their combined contribution does not exceed the aggregated contribution of previously calibrated elements, thus eliminating the need for redundant capacitors and reducing resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional reference capacitors are added to increase the maximum measureable voltage for calibration, then calibration accuracy is improved, but power consumption and area increase during runtime
Solution Approach 1:
The capacitor array is segmented into multiple groups, with each group having an associated reference capacitor. During calibration, only the necessary reference capacitors are activated based on the detected capacitor weight deviations. During runtime, only the minimal required reference capacitors remain active, reducing power consumption while maintaining calibration accuracy.
Solution Approach 2:
The system dynamically configures the capacitor array and reference capacitor connections based on calibration results. Switching elements reconfigure which reference capacitors are active during calibration versus runtime, allowing the system to adapt its resource usage to actual needs rather than maintaining fixed overhead.
2Measurement precision
If additional reference capacitors are added to increase the maximum measureable voltage for calibration, then calibration accuracy is improved, but area increases
Solution Approach 1:
The capacitor array is divided into multiple groups sharing common reference capacitors. This segmentation allows the system to achieve extended measurement range through coordinated use of shared resources rather than dedicating separate reference capacitors to each capacitor, reducing total area requirement.
Solution Approach 2:
Reference capacitors serve multiple functions: they are used during calibration to measure capacitor weight deviations, and during runtime to maintain the necessary voltage ranges for accurate conversion. This multi-functionality eliminates the need for separate dedicated reference capacitors that would only be used during calibration.
3Manufacturing precision
If capacitor weights exceed the aggregated contribution of previously calibrated capacitors, then higher resolution is achieved, but calibration becomes infeasible
Solution Approach 1:
The system extends the calibration capability by adding reference capacitors that provide an additional dimension of voltage range. This allows the calibration process to handle capacitor weights that would otherwise exceed the measurement capability of previously calibrated capacitors alone.
Solution Approach 2:
Reference capacitors act as intermediaries that enable the calibration of high-weight capacitors. By introducing these intermediary elements, the system can indirectly measure and calibrate capacitor weights that would be impossible to measure directly with the existing capacitor array alone.
4Measurement precision
If redundant capacitors are added to account for manufacturing variations, then calibration accuracy is improved, but signal-to-noise ratio decreases
Solution Approach 1:
The capacitor array is segmented into functional groups that are calibrated and activated based on actual manufacturing variations. Only the necessary segments are active during runtime, reducing the total number of capacitors contributing noise while maintaining calibration accuracy for the active elements.
Data Source
AI summary
An uncalibrated converter element in an analog-digital converter may be replaced with two or more smaller elements having an effective total net value that is equal to that of the uncalibrated converter element. In an exemplary case where the element is capacitor, one or more of these smaller capacitors may be independently calibrated by switching the smaller capacitor between two voltages, such as a reference voltage and ground, and then calculating a difference of corresponding digital output codes generated by the backend ADC with previously calibrated capacitors associated with lesser significant bits. The total capacitance of the uncalibrated capacitor may be apportioned between the smaller capacitors so that the individual maximum charge contribution of each smaller capacitor to the converter output together with any expected manufacturing variance does not exceed the aggregated contribution of the previously calibrated capacitors.