Transmitter Optical Module Segmented Grounding for Crosstalk Reduction
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Solution Overview
Problem
Transmitter optical modules face challenges in maintaining high-frequency signal quality and minimizing cross-talk between signal lanes due to limited space for component mounting and parasitic components from bonding wires, which affect characteristic impedance matching and signal propagation.
Innovation Solution
The transmitter optical module design includes multiple laser diodes with independent sub-mounts and drivers, where the cathodes are wire-bonded to signal grounds within the drivers without connection to the chassis ground, and uses a housing with a multi-layered ceramic structure to manage RF and DC terminals efficiently, reducing parasitic components and crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple laser diodes are mounted on a carrier with shared grounding, then device integration is improved, but signal quality and crosstalk control deteriorate
Solution Approach 1:
The patent divides the grounding system into separate signal grounds for each laser diode and a separate chassis ground, rather than using a shared ground. This segmentation prevents ground loops and crosstalk between channels while maintaining high-frequency signal integrity, resolving the contradiction between integration and signal quality.
Solution Approach 2:
The patent extracts the signal ground connections from the chassis ground structure, creating independent signal ground paths for each laser diode. This separation removes the harmful coupling between channels that would otherwise occur through a shared chassis ground, thereby improving signal quality while maintaining device integration.
2Ease of manufacture
If bonding wires are used to connect laser diodes to chassis ground, then assembly is simplified, but parasitic components increase and characteristic impedance matching deteriorates
Solution Approach 1:
The patent removes the direct connection between laser diode cathodes and chassis ground, eliminating the parasitic inductance and resistance introduced by bonding wires to the chassis. Instead, each cathode is connected to its own dedicated signal ground, which maintains proper characteristic impedance matching for high-frequency signals.
3Speed
If laser diodes are driven by high frequency signals exceeding 10 GHz, then transmission capacity is improved, but signal quality degradation increases
Solution Approach 1:
The patent implements separate signal ground paths for each laser diode channel, preventing ground bounce and crosstalk that would otherwise degrade high-frequency signals. This segmented grounding approach maintains signal integrity even when driving multiple laser diodes with high-frequency signals exceeding 10 GHz.
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 enhances the assembly of high-frequency components, minimizes signal degradation, and effectively suppresses cross-talk between signal lanes by independent grounding and optimized interconnections, improving the overall performance of the transmitter optical module.
Implementation Method 1
The cathodes of the LDs are independently wire-bonded to the signal grounds in the respective drivers without connected to the chassis ground
Implementation Method 2
The drivers include respective switching transistors that shunt the driving currents provided to the anodes of the LDs
Data Source
AI summary
A transmitter optical module that implements with two or more laser diodes (LDs) therein is disclosed. The LDs are mounted on a common sub-mount independent of driving circuits and driven by the driving circuits in the shunt-driving mode. The cathode of the LDs are independently, namely, isolated from the ground of the neighbor LDs, connected to the ground within the driving circuits but floated from the chassis ground.