Advanced driver assistance systems (ADAS) rely on high-resolution cameras for surround view, lane sensing and driving decisions. The image sensor outputs its data over MIPI CSI-2, an interface designed for distances of only centimeters inside a camera module. A car needs the video to travel several meters to a central control unit, which is why automotive cameras use a serializer/deserializer (SerDes) link.
In short:
- A serializer at the camera converts the sensor's CSI-2 data into one fast serial stream. A deserializer at the control unit converts it back.
- The same cable carries the video, a slow control channel in the other direction, and often the camera's power.
- The two main families are GMSL (Analog Devices, formerly Maxim) and FPD-Link (Texas Instruments). Both run over coaxial or shielded twisted-pair cable, using FAKRA, Mini-FAKRA (HFM) or HSD connectors.
What a Camera SerDes Does
- Serialization: the serializer takes the multi-lane CSI-2 stream from the sensor and merges it into a single high-speed serial bitstream.
- Control channel: low-speed signals such as I²C and GPIO travel back to the camera over the same cable, so the control unit can set exposure, gain and configuration.
- Power over coax (PoC): DC power is added to the same coaxial conductor that carries the video, so the camera needs no separate power wire.
- Deserialization: the deserializer separates power and control, then rebuilds the CSI-2 data for the processor.
Analog Devices notes that CSI-2 alone is limited to roughly 10 to 15 cm, while GMSL links reach up to about 15 m, which is what makes a remote camera practical.
The Two Main SerDes Families
Gigabit Multimedia Serial Link (GMSL)
GMSL was developed by Maxim Integrated, now part of Analog Devices. GMSL2 supports forward data rates of 3 Gbps or 6 Gbps, with a slow 187.5 Mbps reverse channel. GMSL3 raises the forward rate to 12 Gbps. Links run over coaxial or shielded twisted-pair cable.
FPD-Link
FPD-Link was developed by Texas Instruments. FPD-Link III and FPD-Link IV carry camera video over coaxial or shielded twisted-pair cabling and are designed to meet automotive EMC requirements. For a protocol-level comparison, see our GMSL vs. FPD-Link comparison.
The choice between the two is usually set by the processor or SoC ecosystem the system is built around, not by connector hardware. The cable and connector choices below are broadly the same for both.
Cable and Connector Interfaces
SerDes links need shielded interconnects that keep a controlled impedance, 50 Ω for coax and 100 Ω differential for twisted pair, from the camera to the control unit.
- Standard FAKRA: Single-port coaxial connector in a color-coded, keyed housing. Typically specified up to a few GHz, so check the datasheet for the exact part.
- Mini-FAKRA / HFM: A smaller, higher-frequency version. Molex lists HFM as supporting up to 20 GHz and 28 Gbps, with up to 80% space savings over traditional FAKRA, in single, dual, dual-stack and quad configurations.
- HSD: Shielded four-pin differential connector used with shielded twisted-pair cable.
- Coaxial cable: preferred for cameras because PoC lets one center conductor carry both power and video. Molex lists RG174, RTK031 and RTK044 50 Ω cables for its HFM system.
- Shielded twisted pair: used with HSD connectors where a differential link is chosen.
- Mini-FAKRA / HFM: the usual choice for control units that gather several camera feeds, because quad connectors fit many inputs in one housing.
For more on these connector families, see our guides to FAKRA RF connectors and Mini-FAKRA and HFM connectors, and our guide to coaxial cable types.
What Limits Cable Length
- Insertion loss: conductor and dielectric losses rise with frequency, so a faster link tolerates less cable. The SerDes chips use equalization to recover the signal, but only within limits.
- Return loss and impedance steps: poorly crimped connectors, tight bends and in-line connectors create reflections that close the eye diagram at the receiver.
- Power over coax voltage drop: the current for the camera flows through the thin center conductor, so the voltage drops along the cable (I × R). The supply voltage at the control unit has to be high enough that the camera still receives its required voltage at the far end.
- EMC and shielding: shield quality and connector shielding affect both emissions and immunity.
For the physics behind these losses, see our guide to cable impedance. If your design uses an Ethernet-based camera link instead, see automotive Ethernet connectors.
Data rates and connector figures above come from Analog Devices' GMSL material and Molex's HFM product page. Confirm against the datasheets for the exact parts you intend to use.