Capacitive Sensor Shield Compensation for Digital Signal Interference
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Solution Overview
Problem
Capacitive sensor devices, such as Coriolis-based gyroscopes and accelerometers, are susceptible to interference from parasitic capacitive coupling due to low power consumption, leading to signal corruption and instability, especially from digital communication protocols like I2C and SPI, which affect shield voltage and compromise sensor output accuracy.
Innovation Solution
Integration of a compensation circuit within the ASIC die that injects a compensating charge of opposite polarity and similar magnitude to interference signals on the shield, using coupling capacitors and logic inverters to reduce interference and stabilize the shield voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shield is used to reduce interference on the capacitive sensor, then measurement precision is improved, but parasitic capacitive coupling from digital communication signals still corrupts the output signal
Solution Approach 1:
A compensation circuit is introduced as an intermediary between the interfering digital communication signals and the shield. This circuit detects the interference signals and generates compensating signals that are injected into the shield through dedicated bond pads, mediating the interaction between interference sources and the sensor shield to cancel out harmful effects.
Solution Approach 2:
The compensation circuit converts harmful interference signals into beneficial compensating signals. By detecting the interference on the shield and generating opposite-polarity signals, the circuit transforms the harmful electromagnetic coupling into a useful cancellation effect, where the interference itself becomes the basis for creating its own counteractant.
2Use of energy by moving object
If low-power consumption design is implemented, then energy efficiency is improved, but current capability is reduced making the device more susceptible to interference
Solution Approach 1:
The system is segmented into separate functional components: the low-power capacitive sensor die and the interference compensation circuitry on a separate ASIC die. This segmentation allows the sensor to maintain low power consumption while the compensation circuit handles interference mitigation, distributing the functional requirements across multiple specialized components.
Solution Approach 2:
Inter-chip bond wires serve as intermediaries to connect the sensor die to the ASIC die, carrying both sensor output signals and compensation signals. This intermediary connection infrastructure enables the low-power sensor to benefit from enhanced interference protection provided by the separate compensation circuitry without compromising its power efficiency.
3Productivity
If digital communication signals are transmitted through package leads, then data communication capability is improved, but interference signals are imposed on the shield voltage
Solution Approach 1:
The compensation circuit extracts the interference component from the total signal on the shield by detecting it through dedicated bond pads. By separating the interference detection function from the normal sensor operation, the system can identify and compensate for harmful signals without affecting the primary data communication function.
Solution Approach 2:
A feedback mechanism is implemented where the compensation circuit continuously monitors the shield voltage for interference signals and dynamically adjusts the compensating signal injection in real-time. This closed-loop feedback ensures that the communication capability is maintained while actively counteracting interference as it occurs.
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
Significantly reduces interference on the shield voltage, enhancing sensor package robustness and maintaining output signal accuracy by canceling out interference signals, thus improving performance and reliability.
Implementation Method 1
Capacitive sensor devices face interference issues due to parasitic capacitive coupling from digital communication signals
Implementation Method 2
a voltage regulator configured to produce a shield voltage and a compensation circuit configured to produce a compensation signal, the voltage regulator and the compensation circuit being electrically coupled to the shield, wherein the voltage regulator is configured to regulate the shield to the shield voltage
Data Source
AI summary
A sensor package includes a first die having a capacitor sensor that includes an active sensing portion and a shield surrounding the active sensing portion. The sensor package further includes a second die that includes a voltage regulator configured to produce a shield voltage and a compensation circuit configured to produce a compensation signal. The voltage regulator and the compensation circuit are electrically coupled to the shield. The voltage regulator is configured to regulate the shield to the shield voltage and the compensation signal produced by the compensation circuit is configured to reduce an interference signal on the shield voltage. The compensation circuit includes one or more coupling capacitors that may be programmable capacitor arrays and calibration methodology entails selecting capacitance values for the programmable capacitor arrays that minimizes the error on an output signal of the sensor package.