Why Standardized SerDes Interfaces Are Essential for In-Vehicle Networks

June 17, 2025

Blog

Today, automotive technology is advancing faster than ever, with the latest electronic components now central to the design and success of new vehicles.

Rapidly evolving advanced driver-assistance systems (ADAS) and in-vehicle infotainment (IVI) are the stars of many new models, while autonomous driving systems (ADS) are a major focus of development. These innovations require the integration of more cameras, sensors, displays and computing resources from a growing ecosystem of suppliers. The high-speed data interfaces linking these components are also core to the success of these new onboard systems.

SerDes (serializer/deserializer) interfaces convert parallel data into serial data for high-speed, long-distance communication, using simple low-cost cables. In automotive in-vehicle networks, high-speed SerDes interfaces that leverage advanced digital signal processing techniques are used to connect cameras, lidars and in-vehicle displays to their corresponding electronic control units (ECUs).

Use of these SerDes interfaces is essential because they enable:

• High-speed, low-latency data transfer: A SerDes interface allows for the efficient transmission of large amounts of data at high speeds (multiple gigabits per second) and low-latency (microsecond), crucial for safety-critical applications.
• Longer cable lengths: SerDes interfaces can enable longer cable lengths compared with parallel communication interfaces, especially in harsh electromagnetic environments where cables are susceptible to the effects of electromagnetic interference (EMI).
• Reduced wiring: By requiring fewer wires for data transmission, enabling use of low-cost coax or shielded differential pair (SDP) cables, SerDes interfaces simplify wiring harnesses, reduce weight and lower cost.
• Reliability: Link layer protocols can enable ultra-low bit error rates, functional safety and security, enabling OEMs to meet the latest safety and cybersecurity regulations.

With this need to connect an ever-greater number of components, the benefits of an industry-standardized SerDes solution become even more pronounced. Standardization offers greater supply chain flexibility and vendor choice, enhanced interoperability, simplified design complexity, reduced development costs, and improved quality and reliability.

MIPI A-PHY: A Standardized Solution Purpose-Built for Automotive

MIPI A-PHY is the first industry-standard asymmetric SerDes interface designed specifically for the automotive market. A-PHY enables the high-speed transfer of proven higher-layer camera and display protocols, such as MIPI CSI-2 for cameras and MIPI DSI-2 for displays, to operate over low-cost, long-reach cables throughout a vehicle, eliminating the need to use proprietary SerDes “bridges” and PHYs. For automotive OEMs and system integrators, this equates to simplified in-vehicle networks and reduced costs, weight and development time.

First released in 2020, MIPI A-PHY was purpose-built to provide the high performance, high EMI immunity and stringent near-zero latency requirements needed for automotive. The latest version, A-PHY v2.0, features forward-looking enhancements in recognition of increasing bandwidth demands and performance requirements of software-defined vehicles (SDVs), zonal and other emerging vehicle architectures. A-PHY v1.0 was adopted as an IEEE standard and is available as IEEE 2977-2021.

The specification’s key features include:

• Downlink data rates of up to 32 Gbps per channel and uplink data rates of up to 1.6 Gbps per channel. A table showing all A-PHY “speed gears” is shown in Figure 1
• High reliability, with an ultra-low packet error rate of <10-19 over the lifetime of a vehicle
• High resiliency, with ultra-high immunity to automotive EMI effects
• Bounded low latency (maximum 6 microseconds)
• Functional safety, meeting the requirements of ISO 26262
• Support for multiple cable types—coaxial, shielded differential pair (SDP) and star quad (STQ)—enabling dual-downlink 64 Gbps operation
• Long reach – up to 15 meters in length with four inline connectors
• Multiple power over cable options, including support for 48-volt operation
• Protocol adaptation layers (PALs) to support the transport of CSI-2, DSI-2 and VESA DisplayPort/embedded DisplayPort application layer protocols, plus Ethernet, GPIO, SPI and I2C protocols for peripheral device command and control (See Figure 2)
• Support for higher layer end-to-end MIPI CSI-2 camera service extensions (MIPI CSETM) cybersecurity protocols and supporting MIPI Camera Security Framework (See Figure 2)

Growing Ecosystem

There is a growing automotive ecosystem designing products and services around the A-PHY interface, including multiple camera, radar and lidar sensor vendors, platform vendors, silicon vendors, and test and development tool vendors.

To support A-PHY implementers, MIPI is developing a compliance program designed to ensure A-PHY implementations meet the industry’s need for multi-vendor interoperability, exacting requirements around functional safety and challenging design environments in terms of EMI. The initial phase of the program is focused on testing A-PHY physical and link layers, using the recently published A-PHY compliance test suite. Later phases will extend the program to cover the A-PHY protocol adaptation layer specifications, which enable higher-layer protocols to operate seamlessly over the MIPI A-PHY physical link.

MIPI Alliance Enables Royalty-Free Implementation

As with all MIPI specifications, MIPI membership provides royalty-free licenses to implement the applicable MIPI specification, and there are no additional essential patent licenses required for implementation. Beyond A-PHY, MIPI members also have license to the other specifications for use in ADS/ADAS applications such as MIPI CSI-2 for cameras, all the A-PHY protocol adaptation layer specifications, the MIPI Camera Security Framework for protection of camera data streams and MIPI DSI-2 for displays. 

Resources for the Automotive Ecosystem

More information and resources on MIPI A-PHY and related specifications and programs may be found here.