Lange Coupler Peripheral Ground Conductor IC Design
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Solution Overview
Problem
Conventional Lange coupler designs in IC technology face challenges in achieving high voltage coupling coefficient and characteristic impedances while adhering to IC process design rules, particularly due to the close proximity of microstrip lines to the ground plane, which results in narrow strip lines and increased losses, and the additional costs and inefficiencies associated with using the reverse metallisation layer as a ground plane.
Innovation Solution
The implementation of a Lange coupler with an unbroken peripheral ground conductor allows for co-planar signal propagation without a ground plane, enabling compliance with IC process design rules and supporting various packaging configurations, including flip-chip, by using multiple metal layers to position ground conductor strips between central and outer conductors, allowing for both coplanar and microstrip propagation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the first level of metallisation is used to create a ground plane, then a good electrical ground is achieved, but the separation between the ground plane and strip lines results in Lange coupler dimensions that do not comply with IC process design rules and narrow strip lines with higher losses
Solution Approach 1:
The invention transitions from a planar ground plane configuration to a three-dimensional stacked configuration using multiple metal layers. The ground conductor is placed on a second metal layer directly beneath the strip lines on the first metal layer, creating vertical separation while maintaining horizontal proximity. This dimensional change allows the coupler to comply with IC design rules by increasing effective strip line width without increasing horizontal spacing, thereby reducing signal losses while maintaining electrical ground quality.
2Reliability
If the reverse of the die is used as a ground plane, then grounding is achieved, but additional steps of grinding and metallisation are required resulting in increased cost
Solution Approach 1:
The invention incorporates the ground conductor on the second metal layer during the standard IC fabrication process, before final assembly and packaging. This preliminary integration of the ground plane structure eliminates the need for post-fabrication steps such as die grinding and reverse metallisation, thereby reducing manufacturing complexity and cost while ensuring proper grounding from the outset.
3Manufacturing precision
If the strip lines are positioned close to the ground plane, then the desired characteristic impedance is achieved, but the gap between strip lines does not comply with IC process design rules
Solution Approach 1:
The invention resolves this contradiction by moving the ground conductor to a vertical position on a second metal layer beneath the strip lines. This allows the strip lines to maintain their desired proximity to the ground for impedance control while the horizontal gap between strip lines remains sufficiently large to comply with IC design rules. The vertical stacking arrangement decouples the impedance control requirement from the horizontal spacing constraint.
4Manufacturing precision
If narrow strip lines are used to achieve desired impedance, then characteristic impedance is maintained, but signal losses increase
Solution Approach 1:
The invention allows for wider strip lines by positioning the ground conductor on a second metal layer beneath them. The increased width of the strip lines reduces their resistance and associated signal losses, while the vertical ground configuration maintains the necessary electromagnetic field confinement for proper impedance control. This dimensional reconfiguration breaks the direct relationship between strip line width and ground proximity that constrained previous designs.
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
A Lange coupler comprises an unbroken peripheral ground conductor surrounding input, through, coupled and isolated conductor strips coupled to input, through, coupled and isolated ports of the Lange coupler respectively, wherein the peripheral ground conductor and input and through conductor strips are arranged on a first metal layer.