Split Wave Compensation for Open Stubs in Circuit Substrates
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Solution Overview
Problem
Through-hole vias in multilayer circuit substrates cause signal degradation due to open-ended stubs, leading to increased cost and inefficiency in high-speed data communication, as they create excess capacitance and inductance that reflect energy and interfere with signal propagation.
Innovation Solution
The implementation of a circuit substrate design featuring two vias with conductive elements of equal characteristic impedance, where the first via is coupled to a microstrip or strip line, eliminating open stubs and ensuring equal delay characteristics for signal paths, thereby minimizing signal degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If through-hole vias are used to route signals between conductive layers, then signal routing is simplified and manufacturing cost is reduced, but signal degradation occurs due to open-ended stubs creating excess capacitance and inductance
Solution Approach 1:
The via structure is segmented into multiple sections: a first via portion extending from the first conductive layer to the second conductive layer, and a second via portion extending from the second conductive layer to the third conductive layer. The unused portion of the via is divided into two separate stubs (first stub and second stub) that are electrically isolated from each other by the second conductive layer, preventing the formation of a single long open-ended stub that causes signal degradation.
Solution Approach 2:
The invention converts the potentially harmful open-ended stub into a beneficial structure by using the second conductive layer as a ground reference. The first stub (from first conductive layer to second conductive layer) and second stub (from second conductive layer to third conductive layer) are both referenced to the ground plane, transforming them from harmful reflective elements into controlled impedance structures that maintain signal integrity while still providing the manufacturing simplicity of through-hole vias.
2Reliability
If blind vias are used to eliminate open-ended stubs, then signal degradation is reduced, but manufacturing cost increases substantially
Solution Approach 1:
The invention makes through-hole vias multi-functional by designing them to serve both as signal transmission paths and as structures that inherently eliminate the harmful open-ended stub effect. The via structure is configured so that the second conductive layer acts as both a signal/conductive layer and a ground reference plane, allowing the same via structure to provide both signal routing and stub elimination functions that previously required different via types (blind vs. through-hole).
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 effectively reduces signal degradation by ensuring equal impedance and delay across signal paths, maintaining signal integrity without the need for costly blind vias or significant manufacturing process changes, while being compatible with backplane connectors.
Implementation Method 1
first via, second via, first conductive element, and second conductive element have substantially equal characteristic impedance of substantially two times the characteristic impedance of the input signal line
Implementation Method 2
when an electrical signal propagates through data input line 104, the signal reaches via 108 and propagates through upper via portion 112
Implementation Method 3
The signal propagating through stub 114 reflects back and interferes with the signal propagating from data input line 104
Implementation Method 4
Further, such open-ended stubs 114 create excess capacitance and inductance, further degrading signal integrity
Implementation Method 5
Both views are correct. When the open stub is modeled as lumped elements, then we can speak of inductance and capacitance
Data Source
AI summary
In accordance with a first embodiment, the present invention provides a circuit substrate comprising a first surface; a second surface; a first via having a first end near said first surface and a second end near said second surface; a second via having a first end near said first surface and a second end near said second surface; a first conductive element electrically coupling said first end of said first via and said first end of said second via; a second conductive element electrically coupling said second end of said first via and said second end of said second via; an input signal line coupled to said first via; and an output signal line coupled to said second via.