PCB Power-Over-Cable Via Layout for Stub Effect Mitigation
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Solution Overview
Problem
Autonomous driving vehicles face signal reflection and resonance issues due to the stub effect in high-speed data signal paths, which degrade the quality of high-definition camera data transmission, particularly when using power-over-cable (POC) circuits on printed circuit boards (PCBs).
Innovation Solution
The method involves routing a conductive path on the PCB with additional vias to minimize impedance discontinuity, using a power-over-cable circuit that supplies both power and data through a single signal path, reducing the stub effect by creating a continuous path for high-frequency signals, thereby improving data signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If power-over-cable circuit is used to supply power and data through single signal path, then cable complexity is reduced, but signal reflection and resonance increase due to stub effect
Solution Approach 1:
The via structure is segmented into multiple portions (first via portion, second via portion, third via portion) with different diameters along its length. The via has a first diameter at the via hole, a second diameter in the first via portion, a third diameter in the second via portion, and a fourth diameter in the third via portion. This segmentation allows optimization of impedance matching at different levels of the PCB stack, reducing signal reflections while maintaining the simplified single-cable POC architecture.
Solution Approach 2:
Different portions of the via have different diameters tailored to specific locations within the PCB stack. The via diameter varies locally to match impedance requirements at different interfaces (connector interface, intermediate interfaces, sensor interface). This local quality adjustment minimizes impedance discontinuities at critical transition points while maintaining overall signal integrity throughout the high-speed data path.
2Productivity
If high speed data signal paths are used for high definition cameras, then bandwidth utilization is improved, but signal reflection and resonance worsen
Solution Approach 1:
The via diameter is changed as a parameter along its length to optimize impedance matching for high-speed signals. The via transitions from a first diameter at the connector interface through intermediate diameters to a fourth diameter at the sensor interface. This parameter variation compensates for impedance discontinuities introduced by layer transitions and via penetrations, enabling reliable high-bandwidth transmission at frequencies greater than 1 gigabit per second without signal degradation.
Data Source
AI summary
In one embodiment, a printed circuit board (PCB) includes a substrate, one or more signal layers including a first signal layer, a first segment of a transmission line disposed at the first signal layer electrically coupling a first location to a second location, and a first signal via disposed at the second location. The PCB circuit includes a second segment of the transmission line disposed at the first signal layer electrically coupling a third location to a fourth location and a second signal via disposed at the third location. The PCB includes a power-over-cable circuit disposed on a first surface of the substrate and electrically coupled to the first and second signal via, where the first and second segments carry a signal of an image sensor and the first segment carries power from the power-over-cable circuit to the image sensor, where the image sensor is used for an autonomous vehicle.