Automotive Audio Bus (A2B) Protocol:Benefits & Limitations

Introduction : It is digital audio bus technology developed by Analog Devices mainly for automotive systems. It uses single unshielded twisted pair (UTP) cable between a master and multiple slave nodes. It allows synchronous multi-channel audio interface in addition to control/status data using I2C protocol on sharing mode over UTP cable. The bus is optimized for modern automotive applications such as distributed microphones, speakers, active noise cancellation (ANC) and voice control systems requiring high quality synchronized audio with minimal delay.

Key features of A2B Protocol

• Data rate : Up to ~ 50 Mbps
• Node to node distance : Up to ~ 15 meters
• Overall network length : Up to ~ 40 meters
• Uses daisy chain topology with single master and multiple slaves

Image Courtesy : Analog Devices, Inc.

Advantages of A2B protocol

Following are some of the benefits of A2B protocol.

1. It supports reduced wiring weight and cost due to use of single unshielded twisted pair.
2. It is designed to provide deterministic latency (sub 50 microseconds) and synchronous sampling across nodes. Hence it is suitable for active noise cancellation (ANC) or microphone arrays.
3. Master node can supply power over the same twisted pair to slave nodes in some implementations which simplifies system design.
4. A2B protocol offers flexibility of different node types which allows use of simple to complex devices on single daisy chain topology.

Disadvantages of A2B protocol

Following are some of the limitations of A2B protocol.

1. Although 50 Mbps is sufficient for many audio applications, it is not sufficient for high bandwidth audio or future multimedia needs.
2. It supports single master with multiple slaves which means limited topology compared to full networking bus systems.
3. It is developed by Analog Devices which is proprietary and not open standard and hence will have licensing or vendor lock-in considerations.
4. It is cable length is limited and hence may not be suitable for large or distributed vehicle architectures.

A2B Solutions from Analog Devices

Following are different ICs are offered by Analog Devices.

• AD2438/ AD2430/ AD2435/ AD2433/ AD2432/ AD2431 (A2B Transceiver ICs)
• AD2428 (A2B main/subordinate 4 x PDM XCVR w I2S/TDM)
• Visit analog.com website for more information.

Conclusion: In summary, A2B offers a compelling solution for automotive audio distribution by delivering high bandwidth (up to ~ 50 Mbps), very low latency (sub 50 µs), and a simplified daisy chain topology that replaces bulky multi wire harnesses