Parallel Resonant Magnetic Field Circuit for Keyless Entry
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Solution Overview
Problem
Existing magnetic-field generating circuits for keyless entry systems face challenges in achieving long communication distances due to limitations in magnetic-field intensity, requiring increased coil inductance or core length, which complicates the circuit and increases costs, while series resonant circuits struggle with damping resistor-related issues.
Innovation Solution
A magnetic-field generating circuit using a transformer antenna with a parallel resonant circuit, where a secondary coil and resonant capacitor form a parallel resonant circuit, allowing for increased coil current without lengthening the core, and eliminating the need for a damping resistor, thereby enhancing efficiency and output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If series resonant circuit with damping resistor is used, then magnetic-field output is improved, but rise time increases and communication speed decreases
Solution Approach 1:
The patent changes the resonant circuit configuration from series to parallel resonance. In a parallel resonant circuit, the impedance characteristics are opposite to series resonance, allowing the circuit to achieve both high magnetic-field output and fast rise time without requiring a damping resistor. The parallel resonance creates a high impedance at resonant frequency, enabling efficient energy transfer and rapid current buildup.
Solution Approach 2:
The patent inverts the conventional series resonant circuit approach by using a parallel resonant circuit. Instead of connecting the capacitor in series with the coil, the capacitor is connected in parallel, fundamentally changing the circuit's impedance characteristics and resonance behavior to simultaneously achieve high output and fast response.
2Ease of operation
If damping resistor is connected in series to LC circuit, then frequency-current characteristic becomes flat for enhanced usability, but Q value decreases and magnetic-field output is reduced
Solution Approach 1:
The patent changes the circuit topology from series to parallel resonance, which fundamentally alters the relationship between Q value, damping, and output. In parallel resonance, the circuit naturally provides a flat frequency-current characteristic without requiring a series damping resistor, thus maintaining both usability and high magnetic-field output.
Solution Approach 2:
The patent converts the potential disadvantage of parallel resonance (which typically has lower Q value than series resonance) into a benefit by exploiting the high impedance characteristic at resonance. This high impedance enables efficient power transfer and high magnetic-field output while the parallel configuration naturally provides the desired flat frequency response.
3Power
If coil inductance or core length is increased to extend communication distance, then magnetic-field intensity is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the resonant circuit configuration to parallel resonance, which improves the efficiency of magnetic-field generation. This allows the system to achieve the required magnetic-field intensity for extended communication distance without increasing coil inductance or core length, thereby maintaining simple device structure and low cost.
Solution Approach 2:
The patent skips the conventional approach of increasing physical dimensions (coil inductance, core length) to extend communication distance. Instead, it uses parallel resonance to rapidly build up magnetic-field intensity through efficient energy transfer, achieving the same goal without physical expansion or added 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
The solution enables a significant improvement in magnetic-field intensity and efficiency, allowing for longer communication distances without increasing the core length, reducing costs, and simplifying the circuit design.
Implementation Method 1
a transformer antenna that generates a magnetic field... a step-up transformer including a primary coil and a secondary coil
Implementation Method 2
a resonant capacitor connected in parallel to the secondary coil... form a parallel resonant circuit whose resonant frequency is set to be equal to a frequency of the AC voltage
Data Source
AI summary
A magnetic-field generating circuit includes a transformer antenna that includes a transformer including a primary coil and a secondary coil and a resonant capacitor connected in parallel to the secondary coil of the transformer and that generates a magnetic field. Moreover, an AC power supply circuit is provided that supplies an AC voltage serving as a driving voltage to the primary coil of the transformer antenna. The secondary coil and the resonant capacitor form a parallel resonant circuit whose resonant frequency is set to be equal to a frequency of the AC voltage supplied from the AC power supply circuit.