Capacitive Sensor Continuous Self-Test via Multiplexed Tones
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing capacitive microelectromechanical sensors face challenges in implementing continuous self-testing capabilities without increasing parasitic effects and circuit area consumption, especially in analog parts, and require efficient methods to differentiate self-test responses from real inertial acceleration during normal operation.
Innovation Solution
A capacitive sensor with continuous self-testing capability using multiplexing, featuring two inertial channels with distinct self-test tones and multiplexer circuitry, along with self-test control, readout, demultiplexer, and processing circuitry to analyze self-test signals and trigger alarms for error detection, minimizing additional area consumption and parasitic effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous self-testing is implemented in capacitive sensors, then reliability is improved, but parasitic effects and circuit area consumption increase
Solution Approach 1:
The patent implements periodic self-test phases alternating with normal operation phases. During self-test phases, DC bias voltages are applied to capacitive elements to induce periodic motion at specific frequencies, while during normal operation, the sensor responds to inertial signals. This periodic alternation allows continuous monitoring without constant DC bias application, thereby maintaining reliability while limiting parasitic effects to specific time windows.
Solution Approach 2:
The patent applies preliminary action by pre-defining distinct frequency bands for self-test signals versus normal operation signals. The system prepares and applies DC bias voltages in advance during dedicated self-test phases, and uses band-pass filters tuned to these predetermined frequencies to extract self-test responses. This preliminary frequency allocation enables clear differentiation between self-test and operational signals without requiring additional hardware that would increase area consumption.
2Reliability
If continuous self-testing is implemented in capacitive sensors, then reliability is improved, but circuit area consumption increases
Solution Approach 1:
The patent achieves multi-functionality by using the same capacitive elements and readout circuitry for both normal sensing operation and self-testing. The capacitive elements serve dual purposes: detecting inertial signals during normal operation and responding to DC bias-induced periodic forces during self-test phases. The band-pass filters and signal processing circuitry also handle both operational and self-test signals, eliminating the need for separate dedicated test circuitry and thereby minimizing additional area consumption.
Solution Approach 2:
The patent changes operational parameters to enable self-testing without additional hardware. By switching between different bias voltage conditions (zero bias during normal operation, DC bias during self-test) and utilizing distinct frequency domains (low-frequency inertial signals versus high-frequency self-test responses), the system achieves continuous monitoring capability using the existing circuit infrastructure, thus avoiding area expansion.
3Measurement precision
If self-test tones are used to differentiate self-test responses from real inertial signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent transitions from temporal multiplexing to frequency-domain separation by allocating distinct frequency bands to self-test and normal operation. Instead of using separate time slots with complex switching, the system applies DC bias to generate self-test responses at frequencies distinctly different from the inertial signal band. Band-pass filters tuned to these specific frequencies enable clean separation and extraction of self-test responses, achieving precise signal differentiation with simpler circuitry that avoids multiplexer 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
Enables continuous self-testing with minimal parasitic effects and area consumption, effectively differentiating self-test responses from real inertial signals, ensuring reliable operation and error detection in capacitive sensors.
Implementation Method 1
The position of the rotor mass in a reference system is measured by detecting signal capacitance. An electrode attached to or incorporated by the rotor mass and an electrode attached to or incorporated by the stator form a capacitance. When the rotor mass moves relative to the stator or inertial frame of reference, a change in the distance between the electrodes is converted to a change in the capacitance.
Implementation Method 2
a self-test tone, which is fed to the capacitive element only when the respective capacitive element is not being detected
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A capacitive sensor device includes capacitive elements for detecting at least two inertial channels. At least one of the inertial channel comprises at least two self-test tones with distinctive fundamental frequencies. Inertial signals in the at least two inertial channels are caused by change of capacitance in the capacitive elements due to movements of rotor masses. Self-test tones are fed into at least one capacitive element under control of a self-test control module and the at least two inertial channels are temporally multiplexed to allow feeding of the self- test tones during normal operation of the capacitive sensor device. Signals in the inertial channels are processed for extracting self-test signals corresponding to the self-test tones, and the self-test signals are analyzed for self-test purposes. Alarm is triggered if multiple consecutive samples of predefined set of self-test signals indicate error with same polarity.