Auxiliary ADC Calibration for Delay-Domain ADC Nonlinearity
Find Innovative SolutionsGenerate Solutions
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 includes a voltage-to-delay converter, multiplexers, and calibration circuitry to correct non-linearity by comparing outputs with a digital-to-analog converter and updating look-up tables, using an on-chip successive-approximation-register ADC to estimate and correct integral non-linearities.
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 error increases
Solution Approach 1:
The patent performs calibration before normal operation to pre-determine the relationship between delay cell control voltages and actual delay times. The look-up table is populated in advance with correction data that compensates for non-linearities, allowing the main ADC to operate at high speed without real-time correction computations.
Solution Approach 2:
The patent introduces an auxiliary ADC as an intermediary device to measure the actual delay times accurately. This auxiliary ADC provides reference measurements that mediate between the delay domain ADC's high-speed operation and the need for precision, enabling separate calibration of the delay-to-digital conversion characteristics.
2Ease of manufacture
If calibration path and functional path are separate, then calibration can be performed, but non-linearity mismatch between paths increases
Solution Approach 1:
The patent merges the calibration path and functional path by having the auxiliary ADC share the same delay line and voltage-to-delay converter as the main ADC. This integration ensures that both paths experience identical non-linearities in the voltage-to-delay conversion, eliminating mismatches between calibration and functional paths while maintaining separate measurement capabilities.
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 multi-functional: it serves both as a calibration reference device for measuring delay times and as a functional converter for processing actual input signals. This dual functionality justifies the additional area by providing ongoing utility beyond mere calibration, improving area efficiency.
4Speed
If delay line is used for voltage-to-delay conversion, then high-speed conversion is achieved, but non-linear delay control increases
Solution Approach 1:
The patent changes the parameter being measured from the control voltage itself to the actual delay time produced. By measuring the output parameter (delay time) rather than assuming linearity from the input parameter (control voltage), the system compensates for non-linearities in the voltage-to-delay conversion process through the look-up table correction.
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.