CDC Linearity Testing Using Permuted On-Chip Test Capacitors
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Solution Overview
Problem
Existing automatic test equipment struggles to accurately measure the linearity of capacitive-to-digital converters in capacitive sensors, as it cannot directly source or measure capacitance, making it difficult to verify defect-free production.
Innovation Solution
A method and system that utilize multiple test capacitors applied in various permutations to the inputs of the capacitive-to-digital converter, with a processor determining errors between expected and actual outputs to assess linearity, and calculating linearity errors for the converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If existing automatic test equipment is used to test capacitive-to-digital converters, then testing can be automated, but measurement precision of capacitance linearity deteriorates because the equipment cannot directly source or measure capacitance
Solution Approach 1:
The patent introduces an intermediary measurement approach where voltage measurements are used as a mediator to indirectly assess capacitance linearity. Instead of directly measuring capacitance with specialized equipment, the system applies known test voltages and measures the resulting currents, which are then processed to evaluate the linearity of the capacitive-to-digital converter. This intermediary method enables standard automated test equipment to achieve precision comparable to direct capacitance measurement.
2Measurement precision
If multiple test capacitors are applied in multiple permutations to evaluate linearity, then measurement precision of linearity improves, but device complexity and test time increase
Solution Approach 1:
The patent segments the linearity evaluation into multiple discrete test permutations, each using a specific combination of test capacitors. Instead of requiring a single complex test setup, the methodology divides the assessment into several simpler measurement steps, where each permutation tests a specific aspect of linearity. This segmentation allows standard test equipment to perform the measurements without requiring complex specialized instrumentation.
Solution Approach 2:
The patent employs periodic application of test signals in a systematic sequence of permutations. Multiple test capacitors are applied in repeating cycles with different configurations, allowing the system to gather comprehensive linearity data through periodic measurements. This approach transforms a potentially complex continuous measurement problem into a series of discrete, manageable periodic test steps that can be automated.
3Measurement precision
If multiple test capacitors are applied in multiple permutations to evaluate linearity, then measurement precision of linearity improves, but loss of time increases due to multiple measurement steps
Solution Approach 1:
The patent maintains continuous useful action during the multi-permutation testing process by systematically progressing through test configurations without idle periods. Each measurement step builds upon the previous one, with test capacitors being reconfigured in a continuous sequence rather than requiring complete teardown and reassembly. This continuous approach minimizes non-measurement time while still gathering all necessary data for comprehensive linearity evaluation.
Data Source
AI summary
Method and system are provided for evaluating linearity of a capacitive-to-digital converter (CDC) of a capacitive sensor integrated circuit chip. The evaluating employs multiple test capacitors, which may be on-chip with the CDC, and includes: obtaining capacitance values for the multiple test capacitors and parasitic capacitances of a first input A and a second input B to the capacitive-to-digital converter; applying the multiple test capacitors in multiple permutations to the first input A and the second input B, and for each of at least some permutations, determining an error between an expected output of the CDC using the obtained capacitance values and an actual measured output of the CDC; and determining linearity error for the CDC using the determined errors for the permutations of applying the multiple test capacitors to the first input A and the second input B of the CDC.