Stack Transformer Winding Layout for Lower IMD3 Distortion
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Solution Overview
Problem
Integrated stack transformers face challenges in minimizing common mode inductance, which contributes to third-order intermodulation distortion (IMD3), affecting signal quality.
Innovation Solution
The design incorporates multiple windings with reduced spacing between them, specifically using a second metal layer to increase mutual inductance by overlapping windings, thereby reducing common mode inductance and enhancing signal quality without increasing chip area or manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the common mode inductance of the integrated stack transformer is increased, then the third-order intermodulation distortion (IMD3) worsens, but the signal quality deteriorates
Solution Approach 1:
The patent introduces a second metal layer above the first metal layer to create three-dimensional overlapping windings. The fourth and fifth windings in the second metal layer overlap with the first and third windings in the first metal layer, respectively. This vertical stacking in the third dimension increases mutual inductance while reducing common mode inductance, thereby improving signal quality and reducing IMD3 without increasing chip area.
Solution Approach 2:
The patent implements nested windings where the fourth winding overlaps the first winding, and the fifth winding overlaps the third winding across different metal layers. This nested configuration maximizes the coupling between windings, increasing mutual inductance and reducing the common mode inductance, which directly addresses the IMD3 issue while maintaining compact chip area.
2Reliability
If multiple windings with reduced spacing are implemented to increase mutual inductance, then common mode inductance is reduced, but the chip area increases
Solution Approach 1:
The patent utilizes the vertical dimension by implementing windings in multiple metal layers (first and second metal layers). The overlapping windings are stacked vertically rather than arranged horizontally, which increases mutual inductance through enhanced magnetic coupling while maintaining a compact chip footprint. This three-dimensional arrangement avoids the chip area expansion that would result from planar expansion.
3Reliability
If overlapping windings are used to increase mutual inductance, then common mode inductance decreases, but the manufacturing complexity increases
Solution Approach 1:
The patent combines multiple windings into a single integrated stack transformer structure using standard multi-layer PCB or semiconductor manufacturing techniques. The first and third windings are formed in the first metal layer, while the fourth and fifth windings are formed in the second metal layer, all within a single device structure. This merging approach simplifies manufacturing by using conventional multi-layer fabrication processes rather than requiring separate assemblies or complex three-dimensional packaging.
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 approach effectively reduces common mode inductance, improves IMD3, and enhances signal quality by increasing mutual inductance of the primary/secondary inductors, while maintaining cost-effectiveness.
Implementation Method 1
The fourth winding substantially overlaps the first winding. The fifth winding substantially overlaps the third winding. A distance between the fifth winding and the fourth winding is less than a distance between the third winding and the first winding.
Data Source
AI summary
An integrated stack transformer is provided, wherein the integrated stack transformer includes a first winding, a second winding and a third winding implemented by a first metal layer, and a fourth winding and a fifth winding implemented by a second metal layer. The second winding is positioned between the first winding and the third winding, the fourth winding substantially overlaps the first winding, the fifth winding substantially overlaps the third winding, and a distance between the fifth winding and the fourth winding is less than a distance between the third winding and the first winding. The first winding, the third winding, the fourth winding and the fifth winding form a part of one of a primary inductor and a secondary inductor of the integrated stack transformer, and the second winding is a part of the other of the primary inductor and the secondary inductor.