MEMS Capacitive Transducer Calibration via On-Chip Capacitance Timing
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Solution Overview
Problem
MEMS capacitive transducers exhibit variations in capacitance due to manufacturing inconsistencies and environmental factors, making it challenging to maintain consistent performance over time, especially in consumer electronics where integration and miniaturization are key.
Innovation Solution
A system comprising a MEMS capacitive transducer with biasing and test circuitry that selectively applies current sources to charge and discharge the transducer, varying the voltage between upper and lower values, and determining capacitance based on the time period of this variation, allowing for accurate capacitance measurement and calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MEMS transducers are manufactured using standard processes, then production volume and integration are improved, but manufacturing precision and uniformity of capacitance values deteriorate
Solution Approach 1:
The patent applies parameter changes by measuring the actual capacitance value of each transducer and using this measured parameter to adjust the bias voltage. This allows the system to accommodate variations in manufacturing while maintaining consistent performance. The bias voltage is adjusted based on the measured capacitance to achieve a target operating point, effectively compensating for manufacturing tolerances.
Solution Approach 2:
The patent implements feedback by measuring the capacitance of each transducer and using this measurement to adjust the bias voltage applied to that transducer. This closed-loop approach ensures that each device operates at its optimal point despite manufacturing variations, resolving the contradiction between high-volume production and manufacturing precision.
2Reliability
If bias voltage is adjusted to compensate for capacitance variations, then performance consistency is improved, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent merges the capacitance measurement function and bias adjustment function into a single integrated calibration circuit. The same circuitry that measures capacitance also generates the adjusted bias voltage, eliminating the need for separate calibration components and reducing overall device complexity while maintaining performance consistency.
Solution Approach 2:
The calibration circuit is designed to perform multiple functions: measuring capacitance, determining the appropriate bias voltage, and applying the adjusted bias. This multi-functional approach reduces the number of separate components needed, thereby reducing device complexity while achieving performance consistency across varying capacitance values.
3Measurement precision
If capacitance measurement is performed using external test circuitry, then measurement precision is improved, but ease of manufacture deteriorates due to additional testing steps
Solution Approach 1:
The patent extracts the capacitance measurement function from external test equipment and integrates it directly into the transducer device. By incorporating on-chip measurement circuitry, the system achieves precise capacitance measurement without requiring separate external testing steps, thereby simplifying the manufacturing process while maintaining measurement accuracy.
Solution Approach 2:
The transducer device performs its own capacitance measurement using integrated circuitry. The device measures its own capacitance value and automatically adjusts its bias voltage based on this self-measurement, eliminating the need for external testing equipment and manual calibration steps, thus improving ease of manufacture while maintaining measurement precision.
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
Enables precise determination and calibration of MEMS transducer capacitance, ensuring consistent performance across devices and over time, even in integrated circuits where space is limited, by effectively measuring and adjusting for variations in capacitance.
Implementation Method 1
biasing circuitry coupled to the first node, operable to provide a biasing voltage to the one or more first capacitive plates
Implementation Method 2
selectively apply one or more current sources to the second node, so as to charge and discharge the MEMS capacitive transducer and so vary a signal based on a voltage at said second node
Data Source
AI summary
The disclosure provides a system, comprising: a MEMS capacitive transducer, comprising one or more first capacitive plates coupled to a first node and one or more second capacitive plates coupled to a second node; biasing circuitry coupled to the first node, operable to provide a biasing voltage to the one or more first capacitive plates; and test circuitry coupled to the second node, operable to: selectively apply one or more current sources to the second node, so as to charge and discharge the MEMS capacitive transducer and so vary a signal based on a voltage at said second node between an upper value and a lower value; determine a parameter that is indicative of a time period of the variation of the signal; and determine a capacitance of the MEMS capacitive transducer based on the parameter that is indicative of the time period.