Inter-ADC Calibration Using Time-Equidistant Triggering
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Solution Overview
Problem
Existing analog-to-digital converters (ADCs) face challenges in accurately measuring differential non-linearity (DNL) and integrated non-linearity (INL) due to the need for specialized printed circuit board designs and equipment, which limits their performance, especially in applications like vehicle state modeling with Kalman filters.
Innovation Solution
A calibration circuit that utilizes a microcontroller-based system with a trigger timer, two ADCs of different types, and a non-linear reference signal generator to perform nonlinear inter-ADC calibration through time equi-distant triggering, allowing for DNL and INL performance characterization without requiring expensive external equipment, enabling measurements during runtime on customer boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If specialized PCB design and external equipment are used for ADC calibration, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses its own internal resources (internal ADC, trigger timer, and processor) to perform the calibration of the external ADC, eliminating the need for specialized external calibration equipment. The microcontroller serves multiple functions including generating trigger signals, capturing ADC outputs, and processing calibration data.
Solution Approach 2:
A non-linear reference signal generator is introduced as an intermediary component that provides a known reference signal for calibration. This reference signal serves as a mediator between the internal ADC and the external ADC under test, enabling comparison and calibration without requiring specialized measurement equipment.
2Measurement precision
If traditional ADC calibration methods are used, then DNL and INL performance can be measured, but the system requires external signal generators and specialized equipment
Solution Approach 1:
The calibration system is fully self-contained within the microcontroller, using its internal ADC and timer resources to calibrate external ADCs. This eliminates dependence on external calibration equipment and enables calibration to be performed directly in the final application environment.
Solution Approach 2:
The calibration circuit can calibrate multiple types of ADCs (successive approximation, flash, pipeline, delta-sigma) using the same internal resources and methodology, making the solution universally applicable across different ADC architectures and final product applications.
3Measurement precision
If external calibration equipment is used, then calibration accuracy is achieved, but ease of operation and integration into final products is reduced
Solution Approach 1:
The microcontroller performs calibration autonomously using its internal resources, requiring no external calibration equipment or specialized PCB designs. The calibration process can be initiated and executed directly on customer boards without additional hardware, greatly simplifying integration and operation.
Solution Approach 2:
The calibration functionality is extracted from external specialized equipment and integrated directly into the microcontroller's internal resources. This extraction eliminates the need for separate calibration instruments and enables direct integration into final product applications.
Data Source
AI summary
A calibration circuit, including: a first analog-to-digital converter (ADC) configured to sample a nonlinear reference signal continuously at an equidistant sampling rate to generate a reference sampled signal; a trigger timer configured to generate trigger signals; a second ADC configured to sample a point of each of the nonlinear reference signal and repeated versions of the nonlinear reference signal in response to the respective trigger signals at equidistantly increasing delays, to generate a device-under-test (DUT) sampled voltage; and processing circuitry configured to estimate a differential nonlinearity (DNL) of the DUT sampled signal, estimate a DNL of the reference sampled signal, and compare the estimated DNL of the DUT sampled signal with the estimated DNL of the reference sampled signal, to generate a DNL performance indication signal of the second ADC.