Automotive high-speed connection standard MIPIA-PHYv2.0 released!

On September 27, the MIPI Alliance announced the release of MIPI A-PHY v2.0, the next version of the automotive high-speed asymmetric serializer-deserializer (SerDes) physical layer interface. Version 2.0 doubles the maximum available downlink data rate on a single channel from 16 Gbps to 32 Gbps, and adds an additional uplink device with an eight-fold increase in speed, supporting up to 1.6 Gbps. These enhancements are designed to support the higher bandwidth requirements of partitions and other emerging architectures in next-generation vehicles.

MIPI A-PHY is designed to provide high-performance connectivity between automotive image sensors and displays and their associated electronic control units (ECUs). It is designed to simplify the integration of a large number of in-vehicle sensors and displays for applications such as advanced driver assistance systems (ADAS), modern digital cockpits, in-vehicle infotainment systems (IVI) and autonomous driving systems (ADS).

A-PHY offers a range of up to 15 meters, unprecedented reliability, ultra-low packet error rate of 10-19 over the life of the vehicle, strong noise immunity, ultra-low latency, and extremely low bandwidth channel requirements. It also forms the basis of the MIPI Automotive SerDes Solution (MASS), an end-to-end framework for connecting cameras, sensors and displays with built-in functional safety, confidentiality and data protection.

Key features of A-PHY v2.0:

MIPI A-PHY v2.0 features forward-looking enhancements to meet the growing bandwidth and performance requirements required by software-defined vehicles (SDVs) as well as regional and other emerging automotive architectures:

PAM4 support is now extended to gear 5 (up to 16 Gbps).

Two new gears, G6 and G7, have been added, using PAM8 and PAM16 encoding, with speeds of 24 and 32 Gbps respectively.

The faster 1.6 Gbps uplink device, which provides more than eight times the data rate of previous uplink devices, supports symmetric 1 Gbps Ethernet channels over the A-PHY link for command and control of automotive peripherals.

For ease of implementation, no changes have been made to the upper layers of A-PHY v2.0, so migration from previous versions will be minimal. Version 2.0 is fully interoperable with A-PHY v1.1 and v1.0, and devices using all three specifications can coexist on the same network.

“MIPI A-PHY continues to evolve, delivering unprecedented bandwidth and greater implementation flexibility, while still maintaining its exceptional noise immunity and resiliency,” said Sanjiv Desai, Chairman of the MIPI Alliance. “This new version enables A-PHY to address an even wider range of speeds and design requirements, and provides a strong roadmap to meet the future needs of the rapidly evolving automotive industry.”

To support testing and implementation, the MIPI Alliance is developing a compliance program to ensure that OEMs and device manufacturers' devices comply with the A-PHY specification, which will be rolled out in phases.

A Deeper Look at MIPI A-PHY and Its Benefits for Automotive

MIPI interface protocols are widely used in the automotive field to connect cameras, sensors, displays and other components to automotive systems-on-chip (SoCs). In September 2020, the MIPI Alliance released MIPI A-PHY SM v1.0, the first asymmetric industry standard, long-distance serializer-deserializer (SerDes) physical layer interface.

In this post, I will take a deep dive into MIPI A-PHY and describe its key features and how they benefit some common automotive applications.

In addition to the benefits of standardization, A-PHY provides unprecedented resiliency and reliability and allows OEMs, Tier 1 suppliers and component suppliers to simplify and streamline camera, sensor and display integration. A-PHY extends the use of CSI-2 and DSI-2 and other upper layer protocols throughout the vehicle while reducing cost, weight, complexity and time to market.

The recent wave of innovation in advanced driver assistance systems (ADAS), in-vehicle infotainment (IVI), and autonomous driving applications has made standardized interfaces more important than ever. The number of automotive cameras, radars, displays, and even lidar sensors is increasing, significantly increasing the bandwidth requirements of current solutions.

Today’s proprietary long-reach SerDes options force vendors to spend time and resources adapting to a specific vendor solution, which slows down the development of new architectures and the growth of the ecosystem. Standardization will enable component vendors, Tier 1 suppliers, and OEMs to focus on innovation while also providing them with more choice, scalability, and interoperability within the larger ecosystem.

Two possible applications of A-PHY—high-resolution, low-latency backup cameras and front-facing cameras for lane keeping—show how the specification can help make cars safer. I'll describe these applications in more detail below. Other potential applications include virtual rearview mirrors; 360-degree camera, lidar, and radar systems; and high-resolution instrument, control, and entertainment displays.

MIPI A-PHY v1.0 provides an asymmetric data link in a point-to-point or daisy-chain topology, including high-speed unidirectional data, embedded bidirectional control data, and optional power over a single cable (coaxial or shielded twisted pair). Its main task in automotive systems is to transmit data between cameras and displays and their associated ECUs corresponding to ADAS or IVI functions. With a range of up to 15 meters, it will eventually allow higher-layer protocols such as CSI-2 and DSI-2 to run directly on the physical link that spans the entire vehicle.

Prior to the release of A-PHY, the CSI-2 and DSI-2 protocols implemented in cameras and displays have used the MIPI C-PHY SM or MIPI D-PHY SM short-reach physical layer to connect to a SerDes "bridge" to implement a proprietary long-reach PHY. With the advent of A-PHY, automotive OEMs and suppliers can now implement a standards-based long-reach SerDes solution in two phases, as shown in the following figure:

Phase 1 - Initial deployment: Automakers will replace proprietary bridges and SerDes interfaces with A-PHY. Components using C-PHY and D-PHY will still require standards-based A-PHY bridges, which will serve as a stepping stone to enable native interfaces and scalability.

Phase 2 - Future Deployment: As A-PHY adoption increases, vendors will integrate it into sensor and display modules and SoCs, implementing CSI-2 and DSI-2 (and other approved protocols) directly on A-PHY and eliminating bridges entirely. This architecture, combined with hybrid configurations, will enable flexibility, scalability, reduce costs, enable interoperability, and accelerate innovation in the automotive industry.

A-PHY v1.0 provides two profiles and five gears to meet the performance, cost, and complexity requirements of a variety of applications. The profiles and gears are interoperable.

A-PHY has built-in features to enable data protection in an end-to-end solution, helping A-PHY-based applications meet the functional safety requirements of ISO 26262 and allowing designers to build systems that meet common Automotive Safety Integrity Level (ASIL) specifications, from ASIL-B to ASIL-D.

The A-PHY's A-Packet format includes cyclic redundancy checks (CRCs) in the header and trailer, an 8-bit message counter in the header (to detect loss of the A-Packet), and a timeout monitor (to detect loss of communications).

A time-constrained PHY-level local retransmission scheme (RTS) for each A-PHY link allows recovery from corrupted A-packets, resulting in a stable connection. The RTS mechanism is local to the single-hop A-PHY, so the link layer is not aware of it. RTS provides ultra-high immunity to EMI effects: MIPI Alliance testing at independent laboratories has shown that A-PHY links maintain a high level of immunity after years of mechanical stress and cable aging.

This feature enables A-PHY to achieve a packet error rate of less than 10 -19, which equates to less than one error rate over the lifetime of the vehicle. The low overhead of RTS enables A-PHY to achieve a net data rate of approximately 90% in high gear, achieving greater efficiency than other protocols.

A-PHY connects to the upper layer protocol through a standardized protocol adaptation layer (PAL), which converts the upper layer protocol data into A-Packet format. MIPI is developing PALs for CSI-2 and DSI-2, multiple low-speed control protocols, and approved third-party protocols such as VESA embedded DisplayPort/DisplayPort (eDP/DP).

The MIPI Automotive SerDes Solution (MASS) establishes a full-stack solution that will include A-PHY, PAL, upper layer protocols and service extensions that add end-to-end functional safety and security features, including High-Definition Content Protection (HDCP) for display applications.