Capacitance-to-Digital Converter Role Reversal at Saturation
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Solution Overview
Problem
MEMS capacitive sensors have a limited sensing range, which is exacerbated by the saturation of sigma-delta based capacitance-to-digital converters when the capacitance of the sensing capacitor equals that of the reference capacitor, restricting their utility and increasing the size and cost of the converter.
Innovation Solution
The capacitance-to-digital converter dynamically switches the electrical connection between the sensing and reference capacitors upon saturation, effectively reversing their roles to extend the measurement range without increasing the size of the reference capacitor, thereby maintaining high resolution and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the size of the reference capacitor is increased to extend the measurement range, then the measurement range is improved, but the size and cost of the converter increase
Solution Approach 1:
The patent applies inversion by reversing the roles of the sensing and reference capacitors when saturation is detected. Instead of increasing the reference capacitor size to extend measurement range, the system swaps the capacitors' functions, allowing the former sensing capacitor to become the new reference capacitor and vice versa. This enables extended measurement range without increasing overall converter size.
Solution Approach 2:
The patent implements dynamic switching between two operational modes based on saturation detection. The system transitions from a first mode where the sensing capacitor measures capacitance changes to a second mode where the capacitors are swapped, allowing the system to adaptively extend its measurement range beyond the static limitations of a fixed reference capacitor size.
2Measurement precision
If sigma-delta based capacitance-to-digital converters are used to achieve high sensitivity and low power consumption, then measurement precision is improved, but the measurement range is limited due to saturation
Solution Approach 1:
The patent resolves the contradiction between measurement precision and measurement range by inverting the capacitor roles upon saturation detection. This allows the sigma-delta converter to maintain its high sensitivity characteristics while extending the measurable capacitance range through the swapping mechanism, preventing permanent saturation limitations.
Solution Approach 2:
The system dynamically switches between operational modes to overcome the static measurement range limitation of sigma-delta converters. By detecting saturation and transitioning to a swapped capacitor configuration, the system maintains measurement precision while expanding the usable capacitance measurement range beyond what a fixed reference capacitor would allow.
3Adaptability or versatility
If parallel distributed measurement sensing with multiple read-out circuits is implemented to extend measurement range, then measurement range is improved, but device complexity increases
Solution Approach 1:
The patent avoids the complexity of parallel distributed measurement by using a single read-out circuit that dynamically swaps capacitor roles. Instead of implementing multiple simultaneous measurement circuits with different reference capacitors, the system achieves extended measurement range through temporal switching of a single circuit's configuration, significantly reducing device complexity.
Solution Approach 2:
The patent uses dynamic switching of a single read-out circuit to replace what would otherwise require multiple static measurement circuits. By transitioning between two operational modes with swapped capacitor connections, the system achieves the measurement range extension that would traditionally require parallel distributed sensing, but with much lower complexity.
Data Source
AI summary
A capacitance-to-digital converter and an associated method and computer program product are provided that have an extended measurement range. A capacitance-to-digital converter includes first and second capacitors with the second capacitor being configured to measure a change in a value. The capacitance-to-digital converter also includes first and second switches switchably connecting the first and second capacitors, respectively, to a reference voltage while the first and second switches are in a first position such that charge is stored by the first and second capacitors in response to the reference voltage. The capacitance-to-digital converter further includes a saturation detector configured to detect the charge stored by the second capacitor equaling or exceeding the charge stored by the first capacitor and, in response, causing the first and second switches to switch to a second position while continuing to measure the change in the value with the charge stored by the second capacitor.