1. Introduction
This article briefly introduces three components of the A-PHY standard: Lane Configuration, Cable Topology, and Interconnect, following the previous article “MIPI A-PHY: Analysis of Automotive Remote Camera Interface Technology.” These components form the foundation of a high-speed, stable, and interference-resistant in-vehicle communication system, particularly suitable for connections between sensors and controllers such as cameras, radars, and displays.
2. Lane Configuration
The Lane structure of A-PHY includes two end nodes (End Nodes, namely Source and Sink) and the Transmission-Line Interconnect Structure (TLIS) between them. TLIS can utilize cables or PCB traces, providing engineers with flexible wiring options.
The End Nodes contain A-PHY and the End-Node-Interconnect-Structure (ENIS), which may include PCB traces, vias, connectors, ESD circuits, and capacitive coupling; PSE and PD are optional (though generally required, similar to GMSL and FPDLink).
3. Cable Topology
A-PHY supports both unbalanced and balanced cables, as detailed below:
- Coaxial Cable:
Characteristics: Unbalanced coaxial cable
Maximum standard length: 15 meters
Connector requirements: Up to 4 inline connectors
Minimum segment length: ≥30cm
- SDP/STQ (Differential Topology):
SDP: Shielded Differential Pair
STQ: Star Quad / Dual Differential Pair Shielded
Maximum standard length: 10 meters
The choice of these cable types depends on specific application scenarios and performance requirements, providing designers with greater flexibility.
4. Interconnect
In the A-PHY system, the Interconnect section involves key technologies such as power supply and signal separation.
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Power Supply:
PSE: Power Source Equipment
PD: Power Device
PSE and PD are optional, but generally present, similar to GMSL and FPD Link.
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Separation of DC Power and High-Speed Signals
To ensure effective separation of DC power and high-speed signals, A-PHY employs the following technical measures:
1. Separation of High-Speed Signals:
This is achieved through a simple capacitor, as capacitors have very low impedance on both forward and reverse transmission paths, and appear as an open circuit for DC current.
2. Separation of DC Power Signals:
A low-pass filter is used, while ensuring that the current has minimal impact on high-speed signals. The DC impedance is close to 0, allowing regulated current to pass through to power the source module. The high-frequency impedance needs to be greater than 1kΩ (generally, the impedance of cables is 50Ω or 100Ω, so an order of magnitude higher is sufficient) to avoid energy loss and reflection caused by high-speed signals.