Application of High speed Data Transmission Line in GMSL Camera
1. Overview of GMSL Technology
GMSL (Gigabit Multimedia Serial Link) is a high-speed serial interface technology developed by Maxim Integrated (now ADI), specifically designed for automotive and industrial scenarios, supporting long-distance (over 15 meters), high bandwidth (single channel up to 3-6Gbps) video and data transmission. Its core advantages include:
Anti interference capability: Stable transmission in strong electromagnetic interference (EMI) environments is achieved through coaxial cables or shielded twisted pair cables.
Low latency: End to end transmission delay<1ms, meeting real-time requirements.
Multi protocol support: compatible with videos (such as 1080P@60Hz 、 4K), control signal (I2C/SPI), and power supply (PoC, coaxial power supply) integration.
2. The key role of high-speed data transmission lines
In the GMSL camera system, high-speed cables are the core components of the physical layer, directly affecting signal integrity, system reliability, and deployment flexibility. Its core functions include:
High bandwidth transmission: supports multi-channel GMSL aggregation (such as 4 × 6Gbps=24Gbps), meeting the requirements of 8K resolution or high frame rate video.
Long distance coverage: extended transmission distance (up to 30 meters or more) through low loss coaxial cables or optical fibers.
Anti interference design: Multi layer shielding structure (aluminum foil+braided layer) suppresses high-frequency noise in vehicle/industrial scenarios.
3. Selection and design points of high-speed cables
Typical Scheme for Parameter Requirements
Transmission medium coaxial cable (RG174/RG179) or shielded twisted pair automotive grade coaxial cable (such as FAKRA connector)
Single channel bandwidth of 3-6Gbps (supported) 4K@60Hz ）Four channel aggregation achieves 12-24Gbps
Distance 15-30 meters (copper cable)/100 meters (fiber optic) fiber optic conversion module (such as GMSL over Fiber)
Protection level IP67/IP69K (waterproof and dustproof), high temperature resistant (-40 ℃~105 ℃) cable
Mechanical strength anti bending (>5 million cycles) special flexible cable for drag chain system
Key design techniques:
PoC (coaxial power supply): Simultaneously transmitting data and power through coaxial cables (typical 12V/2A), simplifying wiring.
Balance and pre emphasis: Built in signal conditioning chip (such as MAX96705) compensates for high-frequency attenuation during long-distance transmission.
Connector optimization: FAKRA/Zebra connectors ensure shock resistance and reliable plugging and unplugging in automotive environments.
4. Typical application scenarios
Scenario 1: Autonomous driving car camera
Requirement: 8 cameras (front/surround view) to transmit 4K video in real-time to the domain controller with a delay of<50ms.
Plan:
Cable type: shielded twisted pair (100 Ω impedance, AWG26 specification).
Topology: Star shaped connection, with each camera connected to the controller through an independent GMSL link.
Anti interference measures: The outer layer of the twisted pair is wrapped with copper braided mesh and aluminum foil, and the cable spacing is greater than 10cm to avoid crosstalk.
Effect: The transmission error rate is less than 10 ⁻¹ ², meeting the ASIL-B functional safety level.
Scenario 2: 3D Visual Inspection of Industrial Robots
Requirement: Transmission of binocular cameras (4096 × 4096) within a distance of 10 meters 3000@30fps ）The RAW data.
Plan:
Cable type: Fiber optic composite cable (single-mode fiber+4-core power cord).
Conversion module: GMSL SerDes chips (such as MAX9296) convert electrical signals into optical signals.
Redundant design: Dual link hot backup, switching time<10ms.
Effect: Transmission bandwidth of 12Gbps, supporting sub millimeter level detection accuracy.
5. Technical challenges and solutions
Challenge Solution
High frequency signal attenuation using low loss media (such as PE insulation layer)+adaptive equalizer at the receiving end
EMI interference three-layer shielding (aluminum foil+braided layer+metal connector housing)
The cable sheath for mechanical stress damage is made of TPU material, with a bending radius of ≥ 5 × outer diameter
Multi node synchronization achieves nanosecond level clock synchronization through GMSL daisy chain topology
6. Future Trends
GMSL2/GMSL3 upgrade:
GMSL3 supports single channel 12Gbps and aggregate bandwidth up to 48Gbps (meeting the requirements) 8K@120Hz Demand).
Integrated AES-256 encryption to prevent vehicle data from being intercepted.
Popularization of optoelectronic hybrid cables:
Copper cables are used for short distance power supply and control, while fiber optic cables are used for long-distance video transmission (such as vehicle Ethernet+fiber optic fusion).
Wireless GMSL Exploration:
Millimeter wave (60GHz) wireless transmission test, replacing some wired links (restricted scenarios).
The high-speed data transmission line is the "blood vessel" of the GMSL camera system, which supports massive data transmission in scenarios such as autonomous driving and industrial inspection through a high bandwidth, low latency, and strong anti-interference physical layer design. In the future, with the iteration of GMSL technology and the maturity of optoelectronic fusion solutions, high-speed cables will evolve towards higher density, lower power consumption, and intelligent diagnosis, becoming the core infrastructure of machine vision and vehicle electronics.