Variable-Capacitor LC Circuit Tuning for Spread-Spectrum EMI Reduction
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Solution Overview
Problem
Position and proximity sensors using LC circuits often experience significant electromagnetic interference (EMI) due to large voltage swings, which can lead to failure in meeting EMI standards and require extensive requalification testing and design modifications.
Innovation Solution
A controller is provided to adjust the capacitance of an LC circuit by using a spread spectrum function to generate an adjustment value, which is combined with a target value to set the capacitance of a variable capacitor, thereby adjusting the LC circuit frequency to reduce EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LC circuit operates with fixed capacitance to maintain stable frequency, then the circuit frequency remains constant, but electromagnetic interference increases due to large voltage swings
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed capacitance value to a dynamically adjustable capacitance value. The controller continuously or periodically adjusts the capacitance of the variable capacitor based on spread spectrum algorithms, allowing the LC circuit frequency to vary over time. This dynamic adjustment reduces electromagnetic interference by spreading the energy spectrum while maintaining functional frequency stability through controlled variation around a target frequency.
Solution Approach 2:
The patent implements parameter changes by modifying the capacitance parameter of the variable capacitor. The controller changes the capacitance value according to spread spectrum techniques, adjusting it to reduce EMI while maintaining the LC circuit's operational frequency within acceptable ranges. This parameter modulation allows the system to achieve both frequency stability and reduced electromagnetic interference.
2Object-generated harmful factors
If the capacitance is adjusted to reduce EMI, then electromagnetic interference decreases, but the circuit frequency deviates from the target frequency
Solution Approach 1:
The patent employs feedback by implementing a control loop that monitors the actual frequency of the LC circuit and adjusts the capacitance accordingly. The controller receives feedback about the frequency deviation from the target frequency and modifies the variable capacitor's capacitance to correct the deviation while maintaining EMI reduction. This closed-loop feedback mechanism ensures that frequency accuracy is maintained even as capacitance is adjusted for EMI mitigation.
Solution Approach 2:
The system performs self-service through automatic frequency compensation. The controller autonomously adjusts the capacitance to maintain the desired frequency relationship between the LC circuit and the target frequency, without requiring external intervention. The spread spectrum adjustment and frequency relationship maintenance are handled automatically by the control algorithm, allowing the system to self-correct frequency deviations while reducing EMI.
3Object-generated harmful factors
If a variable capacitor is added to enable frequency adjustment, then EMI can be reduced through dynamic capacitance changes, but the device complexity increases
Solution Approach 1:
The patent applies universality by designing the variable capacitor and controller to serve multiple functions simultaneously. The variable capacitor not only adjusts capacitance for EMI reduction but also participates in frequency tuning and stabilization. The controller performs both spread spectrum modulation and frequency relationship management, consolidating multiple functions into integrated components that reduce overall system complexity despite the addition of the variable capacitor.
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 effectively reduces electromagnetic interference by dynamically adjusting the LC circuit frequency, ensuring compliance with EMI standards and minimizing the need for extensive redesign and requalification.
Implementation Method 1
a variable capacitor to couple with an external inductor as part of an LC circuit
Implementation Method 2
the voltage swings of oscillation signals in some position and proximity sensors may be as large as 6-8 volts, peak-to-peak, which may cause a significant amount of electromagnetic interference (EMI)
Data Source
AI summary
A controller and a method is provided for controlling a capacitance of an LC circuit having a circuit frequency including, a variable capacitor to couple with an external inductor as part of an LC circuit, a target value, a spread spectrum function to generate an adjustment value, and a circuit to poll the target value, call the spread spectrum function, and set a capacitance of the variable capacitor based on the sum of the target value and the adjustment value.