Multi-Turn Directional Coupler for High Directivity
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Solution Overview
Problem
Conventional miniaturized directional couplers in RF communications suffer from low directivity due to area limitations, which is undesirable in RF circuit design, especially when integrated on silicon chips for wireless communication devices.
Innovation Solution
A multi-turn directional coupler design is implemented, where the coupled line forms overlapping windings with the main line, with the main line being wider and shorter, and the coupled line being longer and narrower, to enhance directivity while maintaining a small silicon area footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional directional couplers are miniaturized to reduce silicon area, then the silicon area footprint is reduced, but the directivity becomes very low
Solution Approach 1:
The coupled line is configured to form multiple turns (e.g., two turns) that overlap with the main line, transitioning from a single linear coupling section to a multi-dimensional overlapping structure. This multi-turn configuration increases the effective coupling area and interaction length between the main line and coupled line, thereby improving directivity while maintaining a compact silicon footprint.
Solution Approach 2:
The coupled line is positioned to overlap with and be nested within the spatial envelope of the main line's signal path. This nested configuration allows the coupled line to be embedded in the magnetic field of the main line, enhancing coupling efficiency and directivity without requiring additional lateral space, thus resolving the contradiction between small area and high directivity.
2Area of stationary object
If conventional directional couplers are miniaturized to reduce silicon area, then the silicon area footprint is reduced, but the main line losses increase
Solution Approach 1:
By configuring the coupled line to form multiple overlapping turns with the main line, the coupling function is achieved in a compact vertical and lateral arrangement rather than requiring a long horizontal trace. This reduces the total length of the main line needed to achieve the same coupling effect, thereby reducing resistive losses while maintaining a small silicon footprint.
3Reliability
If the coupled line is made longer to improve directivity, then the directivity increases, but the silicon area footprint increases
Solution Approach 1:
The coupled line is folded into multiple turns that overlap with the main line, effectively packing a longer coupled line length into a compact silicon area. This multi-turn configuration increases the interaction length between the main and coupled lines, improving directivity, while the overlapping arrangement minimizes the lateral space required, thus resolving the contradiction between long coupled line length and small silicon footprint.
Solution Approach 2:
The coupled line is nested within the spatial envelope of the main line by forming overlapping turns. This nested configuration allows the coupled line to utilize the magnetic field of the main line more effectively, achieving high directivity with a compact structure that does not require a large silicon area.
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 design achieves higher directivity and reduced main line losses, meeting desired coupling characteristics with a smaller silicon area, outperforming traditional single-turn couplers in terms of directivity and insertion loss.
Implementation Method 1
the coupled line comprises multiple turns forming a winding, and a portion of the winding overlaps with the main line
Implementation Method 2
the main line is wider and shorter, and the coupled line is longer and narrower, to enhance directivity
Data Source
AI summary
A directional coupler disclosed herein may include a main line provided on a substrate, the main line having a first end connected to an input port and a second end connected to an output port. The coupler may include a coupled line disposed on the substrate, the coupled line having a first end connected to a coupled port and a second end to an isolated port. The main line is electrically isolated from the coupled line. The coupled line includes multiple turns forming a winding, and a portion of the winding overlaps with the main line. The coupled line forms a plurality of windings inductively coupled with the main line. The main line and the coupled line are routed to propagate electric signals on both lines in a same direction, and enhance inductive coupling by mutual inductance.