Stepped-Width Co-Spiral Inductor for RF Q-Factor
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Solution Overview
Problem
Conventional inductors in RF front-end modules face challenges in maintaining high quality (Q)-factor due to area constraints and magnetic field compression by ground planes, which reduces their performance and increases insertion loss.
Innovation Solution
A stepped-width, co-spiral inductor structure is designed with narrower trace widths near top and bottom ground planes, reducing the inductor area and improving the Q-factor, while supporting a duplexer in a laminate substrate to enhance RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional inductor structure with uniform trace width is used, then magnetic field distribution is maintained, but area consumption increases and Q-factor deteriorates due to ground plane compression
Solution Approach 1:
The inductor trace width is varied locally: narrower near ground planes to reduce capacitive coupling and magnetic field compression, wider in the center region to maintain magnetic field strength. This local variation optimizes both Q-factor and area utilization without uniform compromise throughout the structure.
Solution Approach 2:
The invention transitions from a two-dimensional planar inductor to a three-dimensional stepped structure by varying trace width across different spatial regions. This dimensional approach allows the inductor to exploit vertical spacing from ground planes while maintaining optimized current distribution, effectively using z-dimension to resolve the area-Q-factor tradeoff.
2Area of stationary object
If inductor area is reduced to meet area constraints, then integration density improves, but magnetic field compression by ground planes increases causing Q-factor degradation
Solution Approach 1:
Different regions of the inductor are assigned different trace widths: narrower traces near ground planes minimize parasitic capacitance and magnetic coupling, while wider traces in the center maximize inductance per unit area. This localized optimization resolves the contradiction between area reduction and Q-factor maintenance.
Solution Approach 2:
The trace width parameter is changed spatially rather than remaining constant. By adjusting this geometric parameter according to position relative to ground planes, the design achieves both compact area and high Q-factor through parameter optimization rather than uniform design.
3Ease of manufacture
If uniform trace width is used throughout the inductor, then manufacturing is simplified, but performance is degraded due to magnetic field compression near ground planes
Solution Approach 1:
The inductor structure implements local quality variation with different trace widths in different regions. While this increases design complexity, the stepped-width pattern can be implemented through standard photolithography masking techniques, maintaining reasonable manufacturability while significantly improving RF performance through localized geometric optimization.
Solution Approach 2:
The inductor trace is segmented into multiple sections with different widths rather than using a uniform design. This segmentation allows each section to be optimized for its specific location relative to ground planes, improving overall performance while remaining compatible with standard multi-layer PCB fabrication processes.
Data Source
AI summary
A stepped-width, co-spiral inductor structure includes a first exterior layer having a first exterior width. The stepped-width, co-spiral inductor structure also includes a first interior layer coupled to the first exterior layer. The first interior layer includes a first interior width that is wider than the first exterior width of the first exterior layer. The stepped-width, co-spiral inductor structure further includes a second exterior layer coupled to the first interior layer. The second exterior layer includes a second exterior width that is narrower than the first interior width of the first interior layer.