Nested RF Balun Traces Reduce Capacitive Coupling
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Solution Overview
Problem
Conventional RF baluns face challenges in achieving high common-mode rejection ratio (CMRR) due to parasitic capacitive coupling between LC resonators, especially at higher frequencies, which affects noise suppression and balance, and requires larger device sizes increasing manufacturing costs and die area.
Innovation Solution
The design involves forming inner and outer conductive traces over a substrate, where the inner trace is wound to exhibit inductive properties and disposed completely within the outer trace, reducing both inductive and capacitive coupling between the traces, thereby optimizing the RF balun's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF balun design with inter-wound or interleaved conductive traces is used to increase mutual coupling, then coupling between inductors is improved, but capacitive coupling between LC resonators increases leading to reduced CMRR
Solution Approach 1:
The inner conductive trace is disposed completely within the outer conductive trace, creating a nested configuration where one inductor is placed inside the other. This nesting arrangement reduces the overlapping area between traces, thereby minimizing parasitic capacitive coupling while maintaining inductive coupling through the shared magnetic field.
Solution Approach 2:
The patent applies different trace configurations to different regions: the inner trace is wound to exhibit inductive property and disposed completely within the outer trace. This local differentiation in trace geometry and positioning optimizes the coupling characteristics by creating regions of high magnetic coupling while minimizing regions of capacitive coupling.
2Reliability
If larger device size is used to reduce capacitive coupling and improve CMRR, then noise suppression is improved, but die area increases leading to higher manufacturing costs
Solution Approach 1:
By nesting the inner conductive trace within the outer conductive trace, the patent achieves a compact configuration that reduces the overall die area required for the RF balun. This nested arrangement allows the inductors to share space efficiently while maintaining the necessary coupling characteristics for noise suppression and high CMRR.
Solution Approach 2:
The patent combines the two inductors into a shared structure where the inner trace is disposed within the outer trace. This merging of spatial resources allows both inductors to coexist in a smaller footprint while maintaining their individual functions and the required coupling characteristics for effective noise suppression.
3Object-generated harmful factors
If inner conductive trace is disposed completely within outer conductive trace, then capacitive coupling is reduced and CMRR is enhanced, but inductive coupling may be reduced
Solution Approach 1:
The nested configuration places the inner conductive trace completely within the outer conductive trace, which reduces capacitive coupling by minimizing trace overlap area. The inductive coupling is maintained through the shared magnetic field generated by the concentric winding patterns, where the magnetic flux from both traces interacts to provide the necessary mutual coupling.
Solution Approach 2:
The patent optimizes the winding patterns, trace widths, and spacing between the inner and outer traces to balance capacitive and inductive coupling. By adjusting these geometric parameters, the design achieves reduced capacitive coupling while maintaining sufficient inductive coupling for RF balun operation.
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 enhances CMRR by up to 10 dB, improves bandwidth, and reduces amplitude and phase imbalance, leading to better noise suppression and efficiency in RF balun performance.
Implementation Method 1
forming an inner conductive trace over the substrate and wound to exhibit an inductive property and forming an outer conductive trace over the substrate around the inner conductive trace and wound to exhibit an inductive property
Implementation Method 2
reducing both inductive and capacitive coupling between the traces, thereby optimizing the RF balun's performance
Data Source
AI summary
A semiconductor device has an RF balun formed over a substrate. The RF balun includes a first conductive trace wound to exhibit inductive properties with a first end coupled to a first terminal of the semiconductor device and second end coupled to a second terminal of the semiconductor device. A first capacitor is coupled between the first and second ends of the first conductive trace. A second conductive trace is wound to exhibit inductive properties with a first end coupled to a third terminal of the semiconductor device and second end coupled to a fourth terminal of the semiconductor device. The first conductive trace is formed completely within the second conductive trace. The first conductive trace and second conductive trace can have an oval, circular, or polygonal shape separated by 50 micrometers. A second capacitor is coupled between the first and second ends of the second conductive trace.