Auxiliary ADC Calibration for Delay-Domain ADC Nonlinearity
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Solution Overview
Problem
Delay domain analog-to-digital converters (ADCs) exhibit non-linear behavior, limiting their performance due to non-linearity mismatches between calibration and functional paths, which existing calibration methods fail to adequately address.
Innovation Solution
An auxiliary ADC-based calibration system that uses a calibration processor to estimate and correct integral non-linearities by comparing outputs between the ADC and an auxiliary ADC, updating look-up tables to correct for non-linearities, and employing a digital-to-analog converter to cycle through possible codes and update the tables for accurate conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If delay domain ADC is used for fast conversion, then conversion speed is improved, but non-linearity error increases
Solution Approach 1:
An auxiliary ADC is introduced as an intermediary component with a linear signal path to provide reference samples. This auxiliary ADC acts as a mediator between the non-linear delay domain ADC and the calibration processor, enabling accurate non-linearity estimation without compromising the fast conversion capability of the main ADC path.
Solution Approach 2:
The calibration system is segmented into separate functional paths: a fast but non-linear delay domain ADC path for normal operation, and a separate auxiliary ADC path with linear characteristics for calibration. This segmentation allows each path to optimize for its specific function while the calibration processor integrates their outputs to correct non-linearities.
2Measurement precision
If calibration path and functional path are kept separate, then calibration accuracy is improved, but non-linearity mismatch between paths increases
Solution Approach 1:
The calibration processor dynamically adjusts parameters including gain, offset, and non-linearity correction factors based on comparisons between functional path samples and auxiliary ADC reference samples. These parameter changes enable real-time compensation for non-linearity mismatches between the separate calibration and functional paths.
Solution Approach 2:
A feedback mechanism is implemented where the calibration processor continuously compares outputs from the functional path ADC and auxiliary ADC, then uses this comparison to update correction parameters. This closed-loop feedback ensures that non-linearity mismatches are actively compensated, maintaining reliability despite path separation.
3Measurement precision
If auxiliary ADC is added for calibration, then non-linearity correction is improved, but device area increases
Solution Approach 1:
The auxiliary ADC is designed to be shared across multiple input channels, serving as a universal calibration resource. Instead of dedicating separate auxiliary ADCs to each channel, the same auxiliary ADC sequentially calibrates multiple channels, reducing the total device area while maintaining non-linearity correction capability for all channels.
Solution Approach 2:
The calibration functionality is merged into a unified system where the auxiliary ADC and calibration processor work together to service multiple functional ADC channels. This merging eliminates redundant calibration components and reduces overall device area compared to having independent calibration paths for each channel.
4Reliability
If calibration is performed continuously, then non-linearity correction is maintained, but power consumption increases
Solution Approach 1:
Calibration is performed periodically rather than continuously, with the calibration processor activating at scheduled intervals to update correction parameters. Between calibration periods, the system operates in a lower-power mode using the previously calibrated parameters, thus maintaining non-linearity correction while significantly reducing average power consumption.
Solution Approach 2:
The calibration system is designed to self-manage its operation, with the calibration processor autonomously determining when calibration is needed and executing calibration updates without continuous external control. This self-service approach optimizes the balance between maintaining correction accuracy and minimizing power consumption by avoiding unnecessary calibration operations.
Data Source
AI summary
In an example, a system includes an input channel and a voltage to delay converter (V2D) coupled to the input channel. The system also includes a first multiplexer coupled to the V2D and an analog-to-digital converter (ADC) coupled to the first multiplexer. The system includes a second multiplexer coupled to the input channel and an auxiliary ADC coupled to the second multiplexer. The system includes calibration circuitry coupled to an output of the auxiliary ADC, where the calibration circuitry is configured to correct a non-linearity in a signal provided by the input channel. The calibration circuitry is also configured to determine the non-linearity of the signal provided to the ADC relative to the signal provided to the auxiliary ADC.