Variable LC Capacitance Control for Spread-Spectrum EMI Reduction
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Solution Overview
Problem
Position and proximity sensors using LC circuits generate significant electromagnetic interference (EMI) due to large voltage swings, leading to failure in meeting EMI standards and requiring extensive redesign and requalification, which is costly and resource-intensive.
Innovation Solution
A controller and method for adjusting the capacitance of an LC circuit using a variable capacitor, a spread spectrum function, and a frequency comparator to regulate the circuit frequency, reducing EMI by dynamically varying the capacitance to match a reference frequency.
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 EMI emissions exceed regulatory standards
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed capacitance value to a dynamically variable capacitance that changes over time according to a spread spectrum signal. The variable capacitor is controlled by a controller that modulates the capacitance value based on a spread spectrum function, causing the LC circuit frequency to vary dynamically rather than remain fixed, thereby spreading EMI emissions across a broader frequency range and reducing peak emissions at any single frequency.
Solution Approach 2:
The patent implements parameter changes by modifying the capacitance parameter of the LC circuit. The controller adjusts the capacitance value of the variable capacitor based on a spread spectrum function, which causes the resonant frequency of the LC circuit to vary over time. This parameter modulation spreads the energy spectrum and reduces concentrated EMI emissions, allowing the device to meet regulatory standards while maintaining operational functionality.
2Object-generated harmful factors
If the capacitance is adjusted to reduce EMI emissions, then EMI compliance is achieved, but the circuit frequency deviates from the target frequency
Solution Approach 1:
The patent applies periodic action through the spread spectrum function that modulates the capacitance at specific intervals. The controller periodically adjusts the capacitance value according to the spread spectrum signal pattern, creating a controlled periodic variation in frequency. This periodic modulation spreads emissions over time and frequency while maintaining an average frequency close to the target, balancing EMI reduction with frequency accuracy requirements.
3Object-generated harmful factors
If a variable capacitor is introduced to enable frequency modulation, then EMI emissions are reduced, but the device complexity increases
Solution Approach 1:
The patent implements universality by designing the controller to perform multiple functions: it generates the spread spectrum signal, modulates the variable capacitor, and maintains frequency tracking. The variable capacitor itself serves dual purposes by enabling both EMI reduction through frequency modulation and frequency calibration. This multi-functionality approach reduces the need for separate dedicated components for each function, thereby limiting the increase in 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
Reduces EMI emissions by stabilizing the LC circuit frequency within +/−5% of the target, minimizing redesign costs and resource consumption while maintaining sensor functionality.
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.