Integrated Circuit Capacitance Measurement via Differential Timing
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Solution Overview
Problem
Capacitance measurement systems in tamper detection devices and other applications face accuracy limitations due to process, voltage, temperature, and time-related variations, which affect the reliability of capacitance measurements.
Innovation Solution
An integrated circuit with a current source and reference capacitor is used to inject currents into both a measurement capacitor and a reference capacitor, determining the time it takes for the voltages to reach thresholds, and detecting capacitance changes by comparing the differences in these times, thereby canceling out variations and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitance-based measurement system is used in tamper detection devices, then the reliability of tamper detection is improved, but the measurement accuracy is limited due to process, voltage, temperature, and time-related variations
Solution Approach 1:
The patent introduces a reference capacitor as an intermediary element to mediate the measurement process. By comparing the charging time of the measurement capacitor against the reference capacitor, the system eliminates the need for absolute capacitance values and focuses on relative changes, thereby compensating for environmental variations while maintaining measurement accuracy
Solution Approach 2:
The patent changes the measurement parameter from absolute capacitance value to relative capacitance change. By measuring the difference in charging times between measurement and reference capacitors, the system detects only changes in capacitance rather than absolute values, which eliminates sensitivity to process, voltage, and temperature variations
2Measurement precision
If a differential measurement approach using reference capacitor is used, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the reference capacitor and measurement capacitor into a single integrated circuit structure with shared control logic. Both capacitors are charged using the same current source and controlled by the same control unit, which simplifies the overall circuit architecture while maintaining differential measurement capabilities
Solution Approach 2:
The control unit serves multiple functions: it controls the charging of both reference and measurement capacitors, measures both charging times, and processes the differential signal. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby reducing overall device complexity
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 enhances the accuracy of capacitance measurements by ensuring both measurement paths are affected equally by variations, allowing for reliable detection of capacitance changes, even in tamper detection devices and sensors for physical parameters.
Implementation Method 1
the integrated circuit is configured to: inject, using said current source, a first current in an external measurement capacitor and determine a first amount of time within which a resulting voltage on the measurement capacitor reaches a voltage threshold
Data Source
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AI summary
In accordance with a first aspect of the present disclosure, an integrated circuit (204) is provided, comprising a current source (206) and a reference capacitor (208), the integrated circuit being configured to: inject, using said current source, a first current in an external measurement capacitor (202) and determine a first amount of time within which a resulting voltage on the measurement capacitor reaches a voltage threshold; inject, using said current source, a second current in the reference capacitor and determine a second amount of time within which a resulting voltage on the reference capacitor reaches said voltage threshold; detect a change of the capacitance on the measurement capacitor using a difference between the first amount of time and the second amount of time. In accordance with a second aspect of the present disclosure, a corresponding measurement method is conceived.