Capacitor-Array ADC Self-Test for DNL and INL Measurement
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Solution Overview
Problem
Analog-to-digital converters (A/D converters) suffer from non-linearity due to physical imperfections, leading to differential non-linearity (DNL) and integral non-linearity (INL) issues, which affect their accuracy and dynamic range, and existing methods for measuring these non-linearities are complex and not fully effective.
Innovation Solution
An apparatus and method that utilize a capacitor array with a multistage comparator to perform a self-test by measuring differential voltages between pairs of unit capacitors, converting them to digital form, and calculating DNL and INL, allowing for precise analysis and correction of non-linearity errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional DC-voltage ramp test methods are used to measure DNL and INL, then measurement capability is provided, but the measurement system becomes complex requiring logic analyzers, high-accuracy D/A converters, and high-precision DC sources
Solution Approach 1:
The A/D converter performs self-testing by using its own capacitor array and conversion capabilities to measure its own DNL and INL characteristics, eliminating the need for external complex measurement equipment. The converter converts test voltages generated by its own capacitor array into digital values and processes them through its own conversion logic to determine non-linearity parameters.
Solution Approach 2:
The A/D converter is designed to perform multiple functions: normal analog-to-digital conversion and self-testing for DNL/INL measurement. The same converter circuitry and capacitor array used for signal conversion are also utilized for generating test voltages and measuring non-linearity, making the device multi-functional and reducing overall system complexity.
2Measurement precision
If high-accuracy D/A converter and logic analyzer are used for monitoring, then measurement accuracy is improved, but the cost and complexity of the measurement setup increase
Solution Approach 1:
The A/D converter uses its own internal resources - the capacitor array, comparator, and conversion logic - to perform self-diagnosis and measurement of its non-linearity characteristics, eliminating dependency on external high-accuracy measurement equipment.
Solution Approach 2:
The capacitor array serves as an intermediary element that generates test voltages internally. By switching different capacitor combinations, the converter creates a series of known test voltages that pass through the conversion process, allowing the system to measure its own response without external voltage sources or D/A converters.
3Device complexity
If capacitor array is tested on a unit by unit basis using self-test, then measurement simplicity is achieved, but testing time increases due to sequential measurement of each capacitor pair
Solution Approach 1:
The self-test process operates in periodic cycles, systematically switching through different capacitor pairs in a predetermined sequence. Each cycle tests one pair of capacitors by switching them into the conversion path, recording the result, then moving to the next pair, repeating this periodic process until all capacitors are tested.
Solution Approach 2:
The controller pre-establishes the testing sequence and switching patterns before actual measurement begins. The capacitor array is pre-configured with switchable connections that allow systematic access to each capacitor pair, and the test procedure is pre-programmed to minimize reconfiguration time between measurements.
Data Source
AI summary
An analog-to-digital converter comprising a capacitor array having a plurality of unit capacitors, each having first and second inputs; a comparator having a pair of inputs and at least one output; and a controller configured to couple one input of each unit capacitor of the plurality of capacitors to the inputs of the comparator, and to control a feedback loop between the pair of inputs and the at least one output of the comparator.