Optical Module Impedance Matching via Flexible Board Ground Cutout
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Solution Overview
Problem
Conventional optical modules face challenges in matching the impedance of signal pins and signal lines without an impedance matching circuit, leading to increased parasitic inductance, signal deterioration, and the need for additional components, which complicates high-frequency signal transmission and increases costs.
Innovation Solution
An optical module design featuring a flexible board with a cut-out portion in the region facing the header, where the ground conductor is removed, allowing the header to function as a ground conductor and adjusting the distance between the signal line and the header to match the impedance of the signal pin with the signal line, eliminating the need for an impedance matching circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an impedance matching circuit is provided to match the impedance of signal pins and signal lines, then the impedance matching is improved, but the number of parts increases and manufacturing complexity increases
Solution Approach 1:
The ground conductor is extracted (removed) from specific regions of the flexible board to create cut-out portions. This removal modifies the electrical characteristics of the signal line to achieve impedance matching without requiring additional impedance matching circuits or components.
Solution Approach 2:
The flexible board is designed with non-uniform ground conductor distribution - ground conductors are present in some regions but removed in cut-out portions. This local variation in ground conductor presence creates the necessary impedance transformation along the signal line while maintaining simplicity.
2Reliability
If the gap between the optical module and the printed circuit board is varied, then the parasitic inductance changes, but stable production becomes difficult
Solution Approach 1:
The flexible board provides a dynamic, adaptable connection structure that can accommodate variations in gap distance between the optical module and printed circuit board. The flexibility allows the system to maintain stable electrical characteristics despite manufacturing tolerances in assembly gaps.
3Reliability
If a flexible board is used to connect the optical module and the printed circuit board, then the parasitic inductance is reduced, but a resistor is needed for impedance matching which increases parts count and causes energy loss
Solution Approach 1:
The ground conductor is extracted from specific regions to create impedance transformation zones. This structural modification replaces the need for resistive impedance matching components, eliminating both the additional parts and the associated energy losses while maintaining the parasitic inductance reduction benefits of the flexible board.
Data Source
AI summary
A cut-out portion of a ground conductor is located in a region where a header faces a flexible board from the junction of a signal pin and a signal line and faces the signal line. The size of the cut-out portion is determined so that the impedance of the signal pin is matched to the impedance of the signal line.