SAR ADC Switch-Capacitor Calibration for Mismatch Compensation
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Solution Overview
Problem
Traditional SAR analog-to-digital converters face capacitance mismatch issues, leading to increased production costs and lower performance, as existing calibration methods are either costly or time-consuming.
Innovation Solution
A calibration method and apparatus that utilize a switch capacitor array with a controller and comparator to calibrate capacitance mismatch by recording compensation charge quantities in a lookup table, allowing for effective calibration without additional circuits or complex coding, using the switch capacitor groups to provide compensation charges and adjust the calibration charge quantities based on voltage comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional SAR analog-to-digital converters are used, then smaller unit area and lower power consumption are achieved, but capacitance mismatch occurs which affects resolution
Solution Approach 1:
The patent applies preliminary action by performing capacitance calibration before the actual analog-to-digital conversion process. The calibration process pre-determines the compensation charge quantities needed for each switch capacitor group and stores them in a lookup table, so that during normal operation, the controller can directly retrieve and apply the appropriate compensation without additional real-time calibration steps, thus maintaining both small area and high precision.
Solution Approach 2:
The patent changes the operational parameters of the switch capacitor array by introducing compensation charge quantities that adjust the effective capacitance values. The controller modifies the charge distribution across the switch capacitor groups based on the lookup table data, effectively changing the capacitance parameters to compensate for manufacturing mismatches and achieve accurate conversion.
2Manufacturing precision
If existing capacitance calibration methods are applied, then capacitance mismatch is compensated, but production costs increase and performance is lowered
Solution Approach 1:
The patent implements self-service by enabling the switch capacitor array to perform its own calibration using its existing components. The calibration process utilizes the same switch capacitor groups and comparator that are used for the main conversion function, eliminating the need for separate calibration circuits. The system calibrates itself by measuring its own capacitance mismatches and storing compensation data in an integrated lookup table.
Solution Approach 2:
The patent applies universality by making the switch capacitor array multi-functional. The same switch capacitor groups serve both as the primary conversion elements and as the calibration elements. The comparator is used for both calibration measurements and normal conversion comparisons. This multi-functionality eliminates dedicated calibration hardware, reducing device complexity while maintaining calibration capability.
3Measurement precision
If capacitance calibration is performed using additional circuits, then calibration accuracy is improved, but the converter structure becomes more complex
Solution Approach 1:
The patent extracts the calibration function from separate physical circuits and integrates it into the existing converter structure. Instead of adding external calibration circuits, the method extracts and utilizes the inherent measurement capability of the comparator and the controllable nature of the switch capacitor groups. The calibration process is separated as an independent operational sequence controlled by the controller, which directs the switch capacitor groups through calibration-specific charge distributions and reads the comparator results.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively calibrates capacitance mismatch in SAR analog-to-digital converters, reducing production costs and improving performance by enabling accurate binary search operations without the need for complex calibration circuits or coding, thus enhancing the resolution and efficiency of the converters.
Implementation Method 1
comparing a voltage value received by the first input terminal and a voltage value received by the second input terminal by the comparator
Implementation Method 2
providing a second charge quantity to a second input terminal of the comparator by one of the switch capacitor groups, and providing a compensation charge quantity to the second input terminal of the comparator by at least another one of the switch capacitor groups
Data Source
AI summary
A calibration method includes the following: providing a first charge quantity to a first input terminal of a comparator; providing a second charge quantity to a second input terminal of the comparator by one of multiple switch capacitor groups, and providing a compensation charge quantity to the second input terminal of the comparator by at least another one of the switch capacitor groups; comparing a voltage value received by the first input terminal and a voltage value received by the second input terminal, and outputting a voltage comparison result to a controller; and if the controller determines the charge quantity provided to the second input terminal approximates to the charge quantity provided to the first input terminal based on the voltage comparison result, recording a calibration charge quantity in a lookup table stored by the controller. An analog-to-digital converter and a calibration apparatus are also provided.