Carrier Layout for Electro-Optical Module Using Coplanar Waveguide
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Solution Overview
Problem
Conventional interconnects in PIN-TIA arrays for electro-optical modules lead to significant cross-talk issues, degrading signal integrity due to their compact design and microstrip type connections, especially at high data transmission rates like 25 Gbps, resulting in increased jitter and bit error rates.
Innovation Solution
A carrier layout using coplanar waveguide transmission lines with a central conductor and pair of coplanar conductors connected by isolated conducting islands, forming a ground-net structure that is not connected to the common ground plane, reducing cross-talk by providing a low impedance current return path while allowing biasing of PIN diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If driver and TIA arrays are placed close to each other to reduce size, then the electro-optical module achieves compact design and size reduction, but Transmitter-Receiver cross-talk increases degrading signal integrity
Solution Approach 1:
The ground plane is segmented into multiple isolated ground regions (first ground region, second ground region, third ground region) that are electrically isolated from each other. This segmentation prevents cross-talk between adjacent signal lines by providing separate return paths for different signal pairs, while maintaining compact spacing between driver and TIA arrays.
Solution Approach 2:
Different regions of the ground plane are assigned different functions: the first ground region serves as return path for differential signal pair 1, the second ground region serves as return path for differential signal pair 2, and the third ground region provides isolation. This local differentiation of ground plane properties minimizes electromagnetic coupling between adjacent signal lines while maintaining compact layout.
2Speed
If TIA is placed adjacent to PIN diode to reduce lead capacitance and improve performance, then data transmission speed increases and noise decreases, but Receiver-Receiver cross-talk increases
Solution Approach 1:
The ground plane is divided into separate isolated regions under each TIA device (second ground region under first TIA, third ground region under second TIA). This segmentation provides independent return paths for each receiver, preventing Rx-Rx cross-talk even when TIAs are placed adjacent to PIN diodes for compact high-speed design.
Solution Approach 2:
The isolated ground regions act as intermediary structures between adjacent signal lines and circuits. By providing dedicated return paths through these ground regions, the patent mediates the electromagnetic field distribution to minimize cross-talk between adjacent receivers while maintaining the compact TIA-PIN diode placement required for high-speed operation.
3Productivity
If signal lines are placed close to each other to support multiple channels in compact design, then channel density increases, but electromagnetic coupling between signal lines increases causing cross-talk
Solution Approach 1:
The ground plane is segmented into multiple isolated ground regions positioned between adjacent differential signal pairs. This segmentation creates electromagnetic isolation barriers that reduce coupling between closely spaced signal lines, enabling high channel density in compact multi-channel electro-optical modules while maintaining signal integrity.
Solution Approach 2:
The ground plane structure is locally optimized between each pair of adjacent signal lines by providing isolated ground regions specifically positioned to shield against electromagnetic coupling. This local quality enhancement allows dense packing of multiple channels while minimizing cross-talk through targeted electromagnetic isolation at critical interfaces.
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
The coplanar waveguide interconnects with ground net structure significantly reduce cross-talk effects, lowering jitter and bit error rates, maintaining signal integrity even in compact designs, as demonstrated by reduced s-parameter coupling coefficients and improved eye diagram performance at 25 Gbps.
Implementation Method 1
a coplanar waveguide transmission line comprising: a pair of coplanar conductors; and a central conductor disposed between the pair of coplanar conductors
Implementation Method 2
the coplanar conductors of the pair are electrically connected to each other by at least one conducting island that is isolated from the ground plane layer
Implementation Method 3
The coplanar waveguide interconnects with ground net structure significantly reduce cross-talk effects, lowering jitter and bit error rates
Data Source
AI summary
A carrier layout comprising a substrate comprising a ground plane layer and a coplanar waveguide interconnect disposed onto the substrate. The coplanar waveguide interconnect comprises a pair of coplanar conductors and a central conductor disposed between the pair of coplanar conductors. The coplanar conductors of the pair are electrically connected to each other by at least one conducting island that is isolated from the ground plane layer. The present invention also provides an interconnect structure for coupling an electronic unit to an optical device disposed on a substrate having a ground plane layer, the interconnect structure comprising a pair of coplanar conductors and a central conductor disposed between the pair of coplanar conductors. The conductors of the pair are electrically connected by at least one conducting island that is isolated from the ground plane layer.