Capacitive MEMS Sensor Self-Test Using Periodic Charge Pump
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Solution Overview
Problem
Capacitive microelectromechanical sensors face challenges in generating high voltages for self-test signals without external sources, leading to increased complexity, power consumption, and area usage due to the need for high-ohmic resistive feedback and large capacitors in charge pump circuitry.
Innovation Solution
A capacitive sensor with a switched-capacitor readout circuit and an actuation circuit that uses a high-voltage charge pump and control circuitry to generate a self-test bias voltage, synchronized with readout and reset periods to enable efficient in-field self-testing, reducing the need for external high-voltage sources and minimizing circuit area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-voltage charge pump circuitry is used to generate self-test bias voltage, then local self-test capability is achieved, but circuit complexity increases due to high-ohmic resistive feedback and large capacitors
Solution Approach 1:
The patent implements periodic action by enabling the charge pump circuitry only during dedicated self-test intervals rather than continuously. The controller activates the charge pump to generate high-voltage bias signals during specific test periods, then disables it during normal sensor operation. This periodic activation reduces the operational time of complex circuit components, thereby reducing overall system complexity while maintaining self-test capability.
Solution Approach 2:
The patent applies universality by designing the charge pump circuitry to serve multiple functions: it generates high-voltage bias signals for self-testing the capacitive sensor, and the same circuit can be used to test different components of the sensor system (capacitive element, readout circuit, switch arrangements). This multi-functionality reduces the need for separate dedicated test circuits, thereby reducing overall circuit complexity.
2Reliability
If high-voltage charge pump circuitry with resistive feedback is used, then self-test functionality is enabled, but power consumption increases due to current flow through resistors
Solution Approach 1:
The patent reduces power consumption by implementing periodic action where the charge pump and resistive feedback circuits are activated only during brief self-test intervals rather than continuously. During normal sensor operation, these power-consuming components are disabled, allowing the sensor to function with minimal power draw from the charge pump and associated circuitry.
Solution Approach 2:
The patent applies partial action by using minimal high-voltage generation capability sufficient for self-testing purposes rather than continuously generating maximum voltage. The charge pump operates at reduced power levels during self-test, using just enough voltage to deflect the capacitive element for testing, rather than maintaining full power operation.
3Reliability
If large capacitors are used in charge pump circuitry to enable large current consumption, then self-test capability is improved, but circuit area increases significantly
Solution Approach 1:
The patent reduces circuit area by implementing periodic action where large capacitors are charged during brief self-test intervals rather than requiring continuous high-capacity energy storage. The capacitors in the charge pump circuit are sized to provide sufficient charge during short test periods, allowing smaller capacitor values compared to continuous operation requirements, thereby reducing occupied circuit area.
Solution Approach 2:
The patent applies parameter changes by adjusting the operating parameters of the charge pump circuit during self-test mode. The controller modifies voltage levels, switching frequencies, and capacitor discharge patterns to achieve effective self-testing with reduced capacitor sizes. By changing operational parameters rather than maintaining fixed high-capacity design, the circuit area is significantly reduced.
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
The solution allows for a local self-test capability that alleviates the challenges of high-voltage generation, reducing complexity and power consumption while maintaining effective self-testing functionality, thus enhancing the reliability of capacitive sensors in safety-critical applications.
Implementation Method 1
acceleration-like self-test signals can be generated using electrostatic forces
Implementation Method 2
The actuation circuit part includes a high-voltage charge pump and a high-voltage charge pump control circuitry
Data Source
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AI summary
A capacitive sensor that includes at least one capacitive element and a switched-capacitor readout circuit part for detecting at least one signal capacitance that results from motions of the capacitive element. The self-test bias voltage of the actuation circuit part is coupled to the capacitive element during a first period that is synchronized to the front end reset period and occurs when the self-test of the capacitive sensor is enabled by the self-test controller.