SAR ADC Self-Calibration Using Programmable Capacitance Arrays
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Solution Overview
Problem
Successive-approximation analog-to-digital converters (ADCs) face challenges in calibrating gain and ensuring monotonicity due to capacitance mismatches, leading to errors in signal conversion and accuracy.
Innovation Solution
The implementation of programmable capacitances, such as gain tuning, fine gain tuning, and bridge tuning capacitances, along with self-calibration and self-testing modes, allows for precise calibration and adjustment of capacitance values to match the sampling and conversion ranges, using charge-redistribution techniques and digital-to-analog converters to generate scaled voltage levels for accurate digital signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional fixed capacitance values are used in successive-approximation ADCs, then the circuit design is simpler, but capacitance mismatches cause gain errors and monotonicity issues leading to conversion inaccuracies
Solution Approach 1:
The patent implements programmable capacitance values that can be dynamically adjusted during calibration modes. The capacitance array allows switching between different capacitance configurations to compensate for mismatches and achieve accurate conversion, resolving the contradiction between measurement precision and device complexity by making the system adaptive rather than static
Solution Approach 2:
The patent changes the capacitance parameter from fixed to variable through programmable capacitance arrays. By adjusting capacitance values during calibration modes, the system can compensate for manufacturing variations and achieve precise conversion accuracy while managing complexity through systematic parameter control
2Measurement precision
If programmable capacitance arrays are implemented for calibration, then gain and monotonicity accuracy improve, but the circuit size and transistor count increase
Solution Approach 1:
The patent segments the capacitance array into multiple programmable units that can be independently controlled. This segmentation allows achieving precise gain accuracy through selective activation of capacitance elements while minimizing the total circuit area by only activating the necessary number of elements for each calibration step
Solution Approach 2:
The patent uses partial action by activating only the necessary subset of capacitance elements required for achieving the desired calibration accuracy. Rather than using all capacitance elements simultaneously, the system selectively engages elements based on calibration needs, reducing the effective circuit area while maintaining gain accuracy
3Reliability
If self-calibration modes are added to the ADC, then manufacturing variations are compensated, but the operation time and control complexity increase
Solution Approach 1:
The patent performs calibration actions preliminarily during manufacturing or initialization phases. By completing the self-calibration process before normal operation begins, the system compensates for manufacturing variations in advance, making the conversion process more reliable without adding time loss during actual signal conversion operations
Solution Approach 2:
The patent implements self-service through automatic self-calibration modes that the ADC performs autonomously without external intervention. The system automatically detects and compensates for manufacturing variations using built-in capacitance arrays and control logic, improving reliability while minimizing the time and complexity overhead by integrating calibration functions within the existing ADC architecture
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 enhances the accuracy and resolution of successive-approximation ADCs by compensating for capacitance mismatches, improving signal-to-noise ratio and reducing power consumption through smaller circuit size and reduced high-voltage transistor count.
Implementation Method 1
redistributing charge according to a predetermined digital code by a charge-redistribution digital-to-analog converter (DAC) to generate a scaled voltage level
Implementation Method 2
a gain tuning capacitance configured to store a first portion of the sampled input charge during a second phase of the analog-to-digital conversion and to sequester the first portion during a third phase
Data Source
AI summary
A method for calibrating a successive-approximation analog-to-digital converter (ADC) includes configuring the successive-approximation ADC in a calibration mode of operation. The method includes, while in the calibration mode of operation: determining a digital code corresponding to a programmable capacitance of the successive-approximation analog-to-digital converter, and storing the digital code corresponding to the programmable capacitance in a storage element of an integrated circuit die including the successive-approximation ADC. The programmable capacitance may be a gain tuning capacitance, a bridge tuning capacitance, an offset capacitance, or a monotonicity tuning capacitance.