SAR ADC Self-Calibration for CDAC Mismatch Correction
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Solution Overview
Problem
Successive approximation (SAR) analog-to-digital converters (ADCs) face challenges in achieving high resolution without increasing die size, as existing calibration methods like laser trimming and analog calibration are costly, environmentally dependent, and limited by temperature variations and aging, while self-calibration techniques either increase die size or degrade signal quality.
Innovation Solution
A SAR ADC with a binary-weighted charge redistribution DAC using a self-calibration algorithm, which divides the calibration process into error detection and correction, utilizing two capacitor arrays to generate error correction signals and compensate for mismatch errors, allowing for high resolution while minimizing die size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser trimming is used to improve resolution, then manufacturing precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The system performs self-calibration using the existing capacitor array and comparator without external intervention. The calibration process automatically detects mismatch errors and applies corrections through the same DAC structure, eliminating the need for laser trimming equipment and external calibration sources.
Solution Approach 2:
The invention extracts the calibration function from external processes (laser trimming, external calibration equipment) and integrates it into the ADC itself. The calibration capacitor array and control logic are embedded within the DAC structure, allowing on-chip self-calibration.
2Manufacturing precision
If analog calibration with external signal source is used to improve resolution, then manufacturing precision is improved, but productivity decreases due to time consumption
Solution Approach 1:
The system uses its own internal resources (capacitor array, comparator, control logic) to perform calibration without external signal sources. The calibration process is automated and integrated into the normal operation sequence, eliminating manual intervention and external equipment requirements.
Solution Approach 2:
The calibration function is merged with the normal conversion function. The same capacitor array and comparator used for signal conversion are also used for calibration, eliminating the need for separate calibration hardware and reducing overall system complexity.
3Manufacturing precision
If calibration capacitor array is added to improve linearity, then manufacturing precision is improved, but die area increases
Solution Approach 1:
The capacitor array serves dual purposes: it functions as the primary DAC structure for normal signal conversion and as a calibration structure for error correction. The same capacitors are used for both conversion and calibration operations at different times, eliminating the need for separate calibration capacitors.
Solution Approach 2:
The calibration functionality is merged into the existing capacitor array structure. The calibration process reuses the same capacitors, switches, and comparator used for normal operation, combining multiple functions into a single integrated structure rather than adding separate calibration hardware.
4Area of stationary object
If traditional self-calibration techniques are used to reduce die size, then area is reduced, but signal quality degrades
Solution Approach 1:
The calibration process is segmented into distinct phases (error detection, error correction) that are carefully timed and controlled. The calibration capacitor array is activated only during calibration phases, while the function capacitor array handles normal signal conversion, preventing interference between calibration and signal processing.
Solution Approach 2:
The system uses feedback from the comparator output during calibration to automatically adjust the calibration capacitor array configuration. The digital representation of mismatch errors is fed back to control the calibration process, ensuring accurate error correction without degrading signal quality during normal operation.
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
The solution enables high-resolution ADC operation with reduced die size and improved signal quality, as the self-calibration algorithm effectively corrects capacitor mismatch errors, maintaining accuracy across varying temperatures and ages without the need for external calibration sources.
Implementation Method 1
a binary-weighted charge redistribution DAC
Data Source
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AI summary
A method and apparatus for correcting the offset and linearity error of a data acquisition system. A charge redistribution digital to analog convertor (CDAC) is connected to one of the differential inputs of a comparator whose second input comes from a function CDAC. The calibration algorithm is built into a digital control unit. The digital control unit detects the offset and capacitor mismatch errors sequentially, stores the calibration codes for each error in calibration mode and provides the input-dependent error correction signals synchronized with the binary search timing to adjust the differential input of the comparator and compensate the input-dependent errors present at the output of the non-ideal function CDAC during normal conversions.