Symmetrical Inductor Design for Magnetic Coupling Reduction
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Solution Overview
Problem
The coexistence of multiple inductors on a single integrated circuit chip leads to undesired magnetic coupling, necessitating increased physical separation and larger chip area, which increases costs.
Innovation Solution
The design incorporates a first and second coil of metal trace laid out symmetrically and as mirror images respectively, with capacitive coupling provided by interdigital coupling capacitors between segments of the coils, allowing differential signaling and center taps for voltage or current sourcing, thereby minimizing mutual magnetic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple inductors are placed on a single chip, then the functionality and integration of the integrated circuit is improved, but undesired magnetic coupling occurs between the inductors
Solution Approach 1:
The inductor design employs asymmetric coil winding patterns where adjacent coils are wound in opposite directions (one clockwise, one counter-clockwise). This asymmetric configuration creates opposing magnetic flux directions that cancel each other out, thereby reducing mutual magnetic coupling between adjacent inductors on the same chip while maintaining full functionality.
2Object-generated harmful factors
If physical separation between inductors is increased to reduce magnetic coupling, then magnetic coupling is reduced, but the total chip area and cost increase
Solution Approach 1:
The invention converts the harmful magnetic coupling effect into a beneficial cancellation mechanism by designing adjacent coils with opposite winding directions. The magnetic flux generated by one coil naturally opposes and cancels the flux from adjacent coils, transforming what would be a harmful coupling effect into a useful flux cancellation mechanism that reduces mutual coupling without requiring increased physical separation.
3Object-generated harmful factors
If symmetric mirror-image coil configuration is used, then magnetic flux cancellation is improved, but device complexity increases due to additional coupling capacitors
Solution Approach 1:
The coupling capacitors in the symmetric mirror-image configuration serve multiple functions simultaneously: they provide electrical coupling between corresponding segments of adjacent coils, enable differential signaling operation, and contribute to the overall magnetic flux cancellation mechanism. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity despite the enhanced flux cancellation capability.
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
This configuration reduces overall mutual coupling between inductors, allowing for a more compact and cost-effective integrated circuit by offsetting magnetic flux changes between coils, thus alleviating the need for large physical separation.
Implementation Method 1
a first coupling capacitor configured to provide a capacitive coupling between a first segment within the first coil of the metal trace and a counterpart of the first segment within the second coil of the metal trace; and a second coupling capacitor configured to provide a capacitive coupling between a second segment within the first coil of the metal trace and a counterpart of the second segment within the second coil of the metal trace
Data Source
AI summary
An inductor includes: a first coil of metal trace laid out to be symmetrical with respect to a first axis; a second coil of metal trace laid out to be substantially a mirror image of the first coil of metal trace with respect to a second axis; a first coupling capacitor configured to provide a capacitive coupling between a first segment within the first coil of metal trace and a counterpart of the first segment within the second coil of metal trace; and a second coupling capacitor configured to provide a capacitive coupling between a second segment within the first coil of metal trace and a counterpart of the second segment within the second coil of metal trace.