ADC Self-Test Using Time-Based Capacitor Charging
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Solution Overview
Problem
Current ADC self-testing methods are complex, expensive, and require external voltage references, making them inefficient for verifying the linearity and accuracy of analog-to-digital converters.
Innovation Solution
A method using a constant current source and a capacitor to generate test voltages by charging the capacitor for varying time periods, allowing the ADC to convert these voltages into digital values for accuracy and linearity evaluation without external references, utilizing internal microcontroller components like timers and current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external voltage references, operational amplifiers and multiplexers are used for ADC self-testing, then ADC functional testing can be performed, but the system complexity and cost increase significantly
Solution Approach 1:
The patent extracts the essential testing function from complex external circuitry and implements it using only internal microcontroller resources. By removing the need for external voltage references, operational amplifiers, and multiplexers, the solution achieves ADC self-testing using only the microcontroller's internal ADC, timer, and built-in current source, thereby dramatically reducing system complexity while maintaining testing capability
Solution Approach 2:
The patent makes the microcontroller's internal resources serve multiple functions. The internal current source, typically used for other purposes, is repurposed for generating test voltages. The timer is used both for its primary function and for controlling the capacitor charging duration. This multi-functionality eliminates the need for dedicated external testing components, reducing overall system complexity
2Measurement precision
If multiple voltage references and multiplexers are used for ADC self-testing, then linearity verification can be achieved, but calibration maintenance and switching distortion issues arise
Solution Approach 1:
The patent implements self-service by using the microcontroller's own internal resources to generate test signals and perform self-diagnosis. The internal current source charges the capacitor to generate known test voltages, and the internal ADC converts these voltages back to digital values for linearity verification. This eliminates the need for external calibrated voltage references and manual calibration procedures, making the system self-sufficient and easier to operate
Solution Approach 2:
Instead of using external voltage references to test the ADC, the patent inverts the approach by using the ADC itself to measure internally generated voltages. The microcontroller generates precise test voltages through its internal current source and capacitor, then uses the ADC to convert and verify these voltages. This inversion eliminates multiplexer switching and external reference calibration issues while achieving the same linearity verification goal
3Reliability
If external voltage references and components are used for ADC self-testing, then test coverage can be achieved, but cost and component count increase
Solution Approach 1:
The patent merges the ADC testing function with the microcontroller's existing internal resources. By combining the internal current source, capacitor, timer, and ADC into a unified self-testing system, the patent eliminates the need for separate external testing components. This merging reduces component count, lowers manufacturing cost, and maintains comprehensive ADC transfer function verification capability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a low-cost, accurate, and reliable method for ADC self-testing, verifying the ADC transfer function and linearity using internal microcontroller circuits, eliminating the need for external components and ensuring precise time-based voltage generation.
Implementation Method 1
coupling a constant current source to a discharged capacitor for a time period; converting a voltage on the capacitor after the time period
Data Source
AI summary
A constant current source, a stable time base and a capacitor are used to self-check operation of an analog-to-digital convertor (ADC) by charging the capacitor for a pre-determined amount of time to produce a voltage thereon. This voltage will be proportional to the amount of time that the capacitor was charged. Multiple points on the ADC transfer function can be verified in this self-check procedure simply by varying the amount of time for charging of the capacitor. Relative accuracy among test points may then be easily obtained. Absolute accuracy may be obtained by using an accurate clock reference for the time base, a known current source and capacitor value.