SGS Channel PCB Trace Design for Signal Integrity
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Solution Overview
Problem
High-speed signal transmission in electronic circuits faces challenges due to signal integrity issues caused by crosstalk, mutual inductance, and impedance mismatch, particularly in leadframe packages and 2-layer PCBs, which result in poor signal fidelity and increased noise immunity problems.
Innovation Solution
The implementation of a SGS or GSGSG channel circuit design in printed circuit boards and chip packages, featuring a pair of differential signal traces sandwiched by ground guard lines and an intervening reference trace, which helps in achieving optimal differential-mode and common-mode impedance matching, conforming to specifications like MHL, using a cost-effective 2-layer PCB without sacrificing routing space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional trace routing is used in leadframe packages and 2-layer PCBs, then routing space is limited and manufacturing is simple, but signal integrity deteriorates due to crosstalk, mutual inductance, and impedance mismatch
Solution Approach 1:
The patent introduces an intervening reference trace between adjacent high-speed signal leads. This reference trace acts as a mediator that provides a controlled impedance pathway and reduces mutual inductance between differential pairs, thereby improving signal integrity without requiring complete redesign of the package structure
Solution Approach 2:
The patent applies different trace configurations to different regions of the package. Specifically, intervening reference traces are placed between adjacent high-speed signal leads where crosstalk is most problematic, while other areas maintain conventional routing. This localized approach improves signal integrity where needed without unnecessarily increasing overall complexity
2Reliability
If more ground guard lines and reference traces are added to improve impedance matching, then signal fidelity improves, but routing space consumption increases
Solution Approach 1:
The intervening reference trace serves multiple functions simultaneously: it provides impedance control for adjacent differential pairs, acts as a shield against crosstalk, and establishes a defined reference plane. This multi-functionality allows the trace to improve signal fidelity without requiring additional dedicated ground guard lines that would consume more space
Solution Approach 2:
The patent combines the functions of reference plane, shielding, and impedance control into a single intervening reference trace structure. By merging these functions rather than implementing them as separate elements, the design achieves improved signal fidelity while minimizing the area consumed by the trace pattern
3Ease of manufacture
If leadframe packages with conventional routing are used, then manufacturing cost is low and ease of manufacture is high, but noise immunity and signal integrity are poor
Solution Approach 1:
The intervening reference trace serves as an intermediary element that can be easily integrated into conventional leadframe package manufacturing processes. It provides noise reduction and crosstalk mitigation through its position between differential pairs, achieving improved electromagnetic performance without requiring complex manufacturing steps or specialized equipment
Data Source
AI summary
A printed circuit board (PCB) assembly includes a PCB having a core substrate, a plurality of conductive traces on a first surface of the PCB, and a ground layer on the second surface of the PCB. The conductive traces comprise a pair of differential signal traces. An intervening reference trace is disposed between the differential signal traces. A connector is disposed at one end of the plurality of conductive traces. A semiconductor package is mounted on the first surface at the other end of the plurality of conductive traces.