Frequently Asked Questions

MIPI A-PHY (originally released to members in September 2020) is the first standardized, asymmetric, long-reach serializer-deserializer (SerDes) physical layer specification targeted for advanced driver-assistance systems (ADAS), autonomous driving systems (ADS), in-vehicle infotainment (IVI) displays and other surround-sensor applications (e.g., cameras, lidar, radar).

A-PHY's primary mission is to transfer high-speed data between cameras and displays and their related ECUs.

A-PHY offers:

• High reliability: Ultra-low packet error rate (PER) of less than 10^-19 for unprecedented performance over the vehicle lifetime
• High resiliency: Ultra-high immunity to EMI effects in demanding automotive conditions
• Long reach: Up to 15 meters
• High performance: Data rate as high as 16 Gbps with v1.0; up to 32 Gbps with support for Star Quad (STQ) cables in v1.1

A serializer/deserializer converts parallel data to serial data (and vice-versa) for fast communication between devices using lower cost cables and connectors. As data rates and speeds increase, SerDes designs become increasingly complex, especially when designing to meet automotive reliability, quality, aging and functional safety requirements.

Prior to the release of MIPI A-PHY, the industry did not have a standard for a long- reach SerDes with the performance, noise immunity and reliability to cover long-distance, high-speed sensor and display links. Sensor links are particularly susceptible to electromagnetic interference, data loss and latency as link bandwidth and distance increase. As such, there is a need for a standard that meets stringent EMC requirements and offers stricter testing to guarantee proper performance and high resilience. 

Currently, MIPI CSI-2® and DSI-2℠ are used extensively within automotive applications. However, without a long-reach physical layer SerDes standard, MIPI protocols have been connected through proprietary "bridge" solutions, adding complexity and design costs, and the inability to source multiple vendors and achieve economies of scale. In addition, there has not been a standard that includes provisions for functional safety and security within the interface design.

The primary benefits of A-PHY are: 

• A-PHY supports long cable lengths and a high data rate.
• A-PHY has enhanced noise immunity.
• A-PHY has an ultra-low packet error rate < 10^-19.
• A-PHY has higher than a 90% net data rate.
• A-PHY can be fully implemented in hardware -- no software stack is required as in some solutions.
• Designed for use with widely implemented protocols and interfaces.
• A-PHY is the first asymmetric industry-standard solution. Most other solutions are proprietary.

Yes. MIPI A-PHY is the only long-reach SerDes standard to support CSI-2 and DSI-2. All available MIPI CSI-2 and DSI-2 versions are supported via protocol adaptation layers (PAL/CSI-2 and PAL/DSI-2).

Yes. MIPI A-PHY supports approved third-party protocols. For instance, as part of this effort, protocol adaptation layers (PALs) have been released for VESA’s DisplayPort and Embedded DisplayPort standards (VESA DP and eDP), as well as for I²C and GPIO. Additional PALs are scheduled to be developed for Ethernet and I3C.

Yes it does. If you use MIPI DSI-2 over A-PHY, it supports VESA-DSC and VDC-M compression. More information can be found in this presentation from the MIPI Automotive Workshop.

MIPI A-PHY can reach up to 15m using coaxial cable with up to four inline connectors. There is no lower limitation for distance. For any other channel, system simulation should reflect the specific system implementation capabilities.

MIPI A-PHY v1.0 supports five speed gears (2, 4, 8, 12 and 16 Gbps) to provide design flexibility.

A-PHY v1.1 doubles the total downlink bandwidth from 16 to 32 Gbps by adding support for Star Quad (STQ) cables that provide dual differential pairs of conductors within a single shielded jacket. This enables two A-PHY ports over a single cable, saving cost, weight and complexity compared with using two separate coaxial or shielded twisted pair cables.

Yes, MIPI A-PHY is defined to support the required functional safety requirements per ISO26262:2018, including message counter, CRC-32, keep-alive mechanism and other provisions to enable creation of a system-level, end-to-end solution.

No. As MIPI A-PHY is designed as a high-speed asymmetric solution, it can complement and be integrated with other network backbones such as Ethernet, CAN, FlexRay and other interfaces.

Yes. A-PHY v1.1 was adopted in December 2021, and the A-PHY Working Group has begun requirements gathering for future releases with data rate increases to 48 Gbps and beyond.

A-PHY serves as the foundation of MASS^SM (MIPI Automotive SerDes Solutions), a family of specifications that when complete, will provide automotive OEMs and their suppliers with end-to-end high-performance connectivity solutions for the growing number of cameras, sensors and displays that enable automotive applications.

More specifically, MASS allows the higher-layer protocols from MIPI (such as MIPI CSI-2 and DSI-2) and third parties (e.g., VESA eDP/DP) to operate over A-PHY physical links spanning an entire vehicle, eliminating the need for proprietary “bridges” and PHYs. For OEMs and system integrators, this equates to simplified in-vehicle networks (i.e., cable harnesses) and reduced costs, weight and development time. System-level engineers will be able to use this architecture to build systems that meet ASIL (Automotive Safety Integrity Level) requirements at any level, from ASIL B to ASIL D.  MASS also will provide end-to-end security to include authentication, integrity and confidentiality for data protection of camera, sensor and display components. Learn more about MASS.

In 2021, IEEE adopted A-PHY v1.0 as IEEE 2977-2021. IEEE is the world's largest technical professional organization dedicated to advancing technology for humanity. A-PHY was adopted because the organization recognized the value that a standardized SerDes interface would offer to the automotive industry. A key benefit of IEEE adopting A-PHY is that it gives non-MIPI members access to the specification, allowing potential implementers to evaluate the interface without requiring them to become a MIPI member. Now that it has been formally adopted by the MIPI Alliance, v1.1 will also be brought forward for adoption as an IEEE standard.

Learn more about MIPI A-PHY and MASS. MIPI Adopter members can download the specification and view available resources, and MIPI Contributor members may also join the A-PHY Working Group to receive communications and participate in development work.