Segmented Capacitor Calibration for SAR ADC Mismatch Errors
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Solution Overview
Problem
The non-integer multiple capacitance value of scaling capacitors in capacitor-capacitor structures leads to capacitance mismatch errors, causing precision issues in high-precision SAR ADCs.
Innovation Solution
A segmented capacitance calibration circuit with first and second calibration units, connected in parallel or series with the scaling capacitor via a selection switch, to adjust capacitance values and offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a scaling capacitor is added to reduce total capacitance area, then capacitor area is reduced by about 8 times, but capacitance mismatch error occurs because the scaling capacitor value is a non-integer multiple of C
Solution Approach 1:
The calibration circuit is divided into multiple calibration units, each handling specific calibration tasks. The first calibration unit calibrates the scaling capacitor, while the second calibration unit calibrates the LSB capacitor array, enabling precise calibration without requiring non-integer capacitor values.
Solution Approach 2:
The calibration circuit performs preliminary calibration of the scaling capacitor and LSB capacitor array before the main conversion process. By pre-calibrating these components using the calibration units, the system eliminates capacitance mismatch errors that would otherwise occur during normal operation.
2Area of stationary object
If non-integer multiple capacitance values are used for scaling capacitor and LSB capacitor, then total capacitance area is reduced, but precision errors occur due to capacitance mismatch
Solution Approach 1:
The calibration units dynamically adjust the effective capacitance values of the scaling capacitor and LSB capacitor array by adding or subtracting small calibration capacitor values. This allows the system to use non-integer multiple capacitance values for area reduction while compensating for precision errors through parameter adjustment.
Solution Approach 2:
The calibration process uses feedback mechanisms where the calibration units measure the actual capacitance values and adjust them accordingly. The selection switch and calibration units work together to provide feedback-based correction, ensuring that even with non-integer capacitance values, the overall conversion precision is maintained.
3Use of energy by moving object
If a scaling capacitor is added to achieve fast response and small power consumption, then power consumption is reduced, but capacitance value matching becomes difficult resulting in errors
Solution Approach 1:
The calibration units act as intermediary components that mediate between the scaling capacitor and the rest of the capacitor array. These intermediary calibration units enable precise capacitance matching by adding or subtracting small capacitance values, solving the matching difficulty while preserving the low power consumption benefits of the scaling capacitor approach.
Data Source
AI summary
A segmented capacitance calibration circuit applied in a pure capacitor array structure includes a first calibration unit, a second calibration unit and a selection switch which are all connected with a scaling capacitor. The first and second calibration units include at least one capacitor, and the selection switch is configured to select the first or second calibration unit to be connected to the pure capacitor array structure. When the first calibration unit is connected to the pure capacitor array structure and in parallel with the scaling capacitor, a negative error calibration is performed on the scaling capacitor. When the second calibration unit is connected to the pure capacitor array structure and in series with the scaling capacitor, a positive error calibration is performed on the scaling capacitor. The nonlinear problem caused by the precision error of the scaling capacitor in the pure capacitor array structure is solved.