ADC Threshold Testing Using Predictive Step Size Adjustment
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Solution Overview
Problem
Testing analog to digital converters is time-consuming due to the need to determine multiple threshold voltages, which can be affected by manufacturing variations and noise, making it challenging to quickly assess and compensate for device variances.
Innovation Solution
A method involving a processor that calculates a step size for subsequent tests based on the difference between ideal and actual digital codes from multiple conversions, allowing for efficient determination of threshold voltages by adjusting input voltages using equations such as the transition intercept equation, and employing multiple conversions per decision to reduce noise effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple analog input voltages are tested to determine each threshold voltage of the device under test, then the threshold voltages can be accurately determined, but the testing process becomes time-consuming
Solution Approach 1:
The system performs preliminary actions by calculating a next input voltage level before actually applying it to the device under test. This calculation uses the transition intercept equation to predict the optimal next voltage level based on previous test results, allowing the system to proactively move toward threshold voltages rather than exhaustively testing all possible levels. This preliminary calculation step reduces the number of actual measurements needed while maintaining accuracy.
Solution Approach 2:
The system implements feedback by using the digital code output from the device under test to inform the calculation of the next input voltage level. The transition intercept equation incorporates the difference between the actual digital code and the expected digital code to adjust subsequent test points. This feedback loop allows the testing process to adapt dynamically, focusing measurements where they are most needed and avoiding redundant tests, thereby reducing overall testing time while maintaining precision.
2Measurement precision
If multiple conversions are performed per test decision, then noise effects are reduced and measurement accuracy improves, but the complexity of the testing process increases
Solution Approach 1:
The testing process is segmented into distinct phases: performing multiple conversions, calculating an average digital code, and using that average to determine the next test decision. This segmentation allows the system to handle the complexity of multiple conversions in a structured way, breaking down the overall testing process into manageable steps that can be executed systematically without overwhelming the control logic.
Solution Approach 2:
The average digital code serves as an intermediary between the multiple raw conversion results and the final test decision. Instead of directly using individual conversion results which may be noisy, the system computes an average as an intermediate value that smooths out noise while preserving the essential information needed for threshold determination. This intermediary step simplifies the decision-making process by providing a single representative value from multiple conversions.
Data Source
AI summary
Methods and apparatus, including computer program products, to test analog to digital converters, are disclosed. In general, data is received that characterizes a first digital code from a device under test at a first analog voltage of an analog signal generator and a second digital code being a digital code threshold, and a step size is generated for another test of the device by performing a calculation by a processor. The calculation may include multiplying a least significant bit size of the device with a difference of the first and second digital codes to generate a product, and dividing the product by a least significant bit size of the analog signal generator. The first digital code may be calculated from results from multiple subtests in the test, where each of the subtests includes multiple analog to digital conversions by the device at the first analog voltage.