TOSA Trace Routing for RF Power Isolation
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Solution Overview
Problem
Optical transceiver modules face challenges in thermal management, insertion loss, and manufacturing complexity due to the inclusion of hermetically-sealed components, which also lead to electrical interference between DC and RF signals as the available space for routing traces shrinks, degrading performance.
Innovation Solution
A transmitter optical subassembly (TOSA) with a hermetically-sealed housing that electrically isolates RF traces from power-related traces by disposing them on opposite sides of a substrate, using a feedthrough device with ceramic material for electrical shielding and minimizing interference, and employing DC bus bars and wire bonding for secure connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hermetically-sealed components are included in TOSA, then optical performance and transmission distance are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent divides the TOSA into distinct hermetic housing and external circuit board sections, with controlled interfaces between them. This segmentation allows the hermetic seal to be applied only where needed for optical components, while keeping the driving circuitry external, thereby reducing overall manufacturing complexity while maintaining optical performance.
Solution Approach 2:
The patent introduces feedthrough devices as intermediary components that provide controlled electrical connections between the hermetic housing and external circuitry. These feedthroughs act as mediators that maintain the hermetic seal while enabling necessary signal and power transmission, simplifying the manufacturing process compared to fully sealed designs.
2Volume of moving object
If trace routing space is reduced to shrink module size, then miniaturization is achieved, but electrical interference between DC and RF signals increases
Solution Approach 1:
The patent utilizes three-dimensional trace routing on the circuit board, employing multiple layers and vertical stacking of conductive paths. This dimensional approach allows DC and RF traces to be routed in different spatial planes, maintaining electrical isolation while minimizing the overall module footprint.
Solution Approach 2:
The patent applies different trace routing strategies in different regions of the circuit board. High-frequency RF traces are routed with specific geometries and spacing in critical areas, while DC power traces use different routing patterns. This localized optimization reduces electrical interference without requiring uniform increases in overall module size.
3Area of stationary object
If DC and RF traces are routed close together to reduce space, then area efficiency is improved, but signal integrity deteriorates due to electrical interference
Solution Approach 1:
The patent extracts RF signal paths from proximity to DC power traces by routing them through separate regions of the circuit board. This separation extracts the harmful electromagnetic coupling between the two signal types, maintaining signal integrity while achieving reasonable area efficiency through optimized layout.
Solution Approach 2:
The patent employs multi-layer circuit board construction where DC and RF traces are placed on different physical layers separated by ground planes and dielectric materials. This vertical dimensionality provides electrical isolation while maintaining compact horizontal footprint, preserving signal integrity without sacrificing area efficiency.
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 configuration minimizes electrical interference between RF and power signals, enhancing the performance and reliability of optical transceivers by maintaining signal integrity and reducing manufacturing complexity while maintaining a hermetically-sealed environment.
Implementation Method 1
electrically isolates RF traces from power-related traces by disposing them on opposite sides
Implementation Method 2
using a feedthrough device with ceramic material for electrical shielding and minimizing interference
Data Source
AI summary
The present disclosure is generally directed to a transmitter optical subassembly (TOSA) having a hermetically-sealed housing with a feedthrough device that electrically isolates RF and power traces. In more detail, a TOSA consistent with the present disclosure includes a substrate with driving circuitry disposed thereon. A first end of the substrate may electrically couple to transmit connecting circuitry and a second end may couple to a hermetically-sealed housing. The hermetically-sealed housing can include one or more laser packages for emitting associated channel wavelengths in addition to monitor photodiodes (PDs), and temperature control devices such as TECs. The hermetic-sealed housing includes a first end with a feedthrough device that provides traces to electrically couple to the circuitry of the substrate. The hermetic-sealed housing further includes an optical coupling port, e.g., a LC connector, for coupling to an external fiber, for example.