New MIPI A-PHY doubles automotive SerDes bandwidth

The Mobile Industry Processor Interface (MIPI) Alliance, which develops physical layer interface specifications for mobile devices, recently unveiled its MIPI A-PHY Version 1.1, the next version of the automotive serializer-deserializer (SerDes) physical-layer interface, which alliance officials say will sharply increase bandwidth between connected sensors and other components in a vehicle.

A-PHY v.1.1, which comes about a year and a half after the original MIPI A-PHY release, promises to double a maximum available downlink data rate of 32 Gbps, twice the 16 Gbps in MIPi A-PHY 1.0. That original spec was first developed to address a growing need for a long-reach, asymmetric SerDes interface to support high-performance links between automotive image sensors and displays and their associated electronic control units at a time when many more sensors are being added to vehicles as part of advanced driver-assistance systems, in-vehicle infotainment solutions and other applications.

“Basically A-PHY is actually the first specification which is really going to standardize the physical layer in the automotive segment,” said Raj Kumar Nagpal, senior manager at Synopsys and co-chair of the MIPI A-PHY Working Group, during last week’s virtual MIPI A-PHY Automotive Industry Forum “Today, there are proprietary solutions… which basically connect bridges and sensors.” 

He explained that these proprietary solutions will go away in the coming years as the A-PHY spec becomes more integrated with sensors, cameras and other devices in the vehicle for a solution that is overall less expensive for auto companies.

The doubling of bandwidth was accomplished 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.

Nagpal also said A-PHY 1.1 supports “different gears” to help auto companies have more downlink and uplink flexibility, and other enhancements. It connects at distances of up to 15 meters with ultra-low latency, noise immunity and an extremely low packet error rate of 10-19 over a vehicle's lifetime. It also forms the foundation of MIPI's Automotive SerDes Solutions (MASS), an end-to-end framework for connecting cameras, sensors and displays with built-in functional safety, security and data protection.

The A-PHY 1.0 spec was adopted as an IEEE standard last year, and MIPI officials said that A-PHY 1.1 also will move toward IEEE adoption, with MIPI Alliance members introducing products supporting A-PHY 1.1 this year.

“If you look down the member list of the MIPI Alliance you'll see a wide range of OEMs Tier 1 companies and other players in the automotive industry who are paid members,” said Peter Lefkin, managing director of the MIPI Alliance. “It's very interesting to see the dynamics at play within the auto industry. One can look back at the evolution of the mobile industry in 2003 to see a bit of a parallel and the importance of standardization and the evolving nature of the ecosystem in the automotive industry.”

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