Auxiliary ADC Calibration for Delay-Domain ADC Linearity
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Solution Overview
Problem
Delay domain analog-to-digital converters (ADCs) exhibit non-linear behavior, which limits their performance and accuracy, and existing calibration methods are hindered by non-linearity mismatches between calibration and functional paths.
Innovation Solution
An auxiliary ADC-based calibration system is introduced, which includes a voltage-to-delay converter, multiplexers, and calibration circuitry. This system compares the output of the main ADC to a reference signal from the auxiliary ADC, estimating and correcting non-linearities by updating look-up tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If delay domain ADC is used for high-speed conversion, then conversion speed is improved, but non-linearity increases
Solution Approach 1:
An auxiliary ADC is introduced as an intermediary device with a separate signal path that has lower non-linearity. This auxiliary ADC measures the input signal independently, and its output is used to calculate correction values that compensate for the non-linearity in the main delay domain ADC, thereby resolving the contradiction between high conversion speed and measurement precision
Solution Approach 2:
A feedback mechanism is implemented where the output of the auxiliary ADC is used to generate correction values that are applied to the main ADC output. The system continuously monitors the non-linearity through the auxiliary path and adjusts the correction lookup table accordingly, creating a closed-loop system that maintains linearity while preserving the high-speed conversion capability
2Measurement precision
If calibration circuitry is added for non-linearity correction, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The auxiliary ADC serves multiple functions: it acts as a reference for non-linearity measurement, provides correction data for the lookup table, and enables continuous calibration without interrupting the main conversion path. This multi-functionality reduces the need for separate dedicated calibration components, thereby limiting the increase in device complexity while achieving improved measurement precision
3Measurement precision
If auxiliary ADC path is added for calibration, then non-linearity correction is improved, but area requirements increase
Solution Approach 1:
Instead of creating a completely separate and complex calibration system, the patent uses a simplified auxiliary ADC path that copies the essential measurement function. This auxiliary path is designed to be less complex than the main path, requiring fewer resources and occupying less area, while still providing sufficient accuracy for non-linearity correction through lookup table implementation
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.