Automobile audio bus optimization for audio applications

While moving, automobiles can be influenced by high temperature, vibration, engine operation, etc, which creates a strict application environment that makes audio signals easily suffer from interference and increases the complexity of cable deployment. Because of this, ADI has launched automobile audio bus (A2B®) technology and products in order to help reduce the design complexity and cost of automobile audio systems. This text will introduce the details of A2B technology and products for you.

A2B technology substantially simplifies the complexity and cost of automobile audio systems

The Electronic Control Units (ECU) of traditional automobile audio are normally linked by individual analog cables or existing digital bus architectures, both of which have limitations like low efficiency and the generation of unnecessary cost. Automobile audio systems using analog wiring require dedicated and expensive shield cable for each audio signal or channel. In the current premium audio systems supporting multichannel Dolby (5.1 or 7.1) or DTS decoding, the required cable quantity is rapidly increasing. What’s more, necessary analog-to-digital converters (ADC) and digital-to-analog converters (DAC) not only increase the total system cost, but also reduce audio performance.

Contemporary infotainment systems have already widely adopted the MOST® or Ethernet AVB digital bus standard, which can substantially simplify the relevant wiring complexity of the analog implementation plan. However, although MOST and Ethernet AVB can improve performance and flexibility, they will add expensive microcontrollers for managing the associated software protocol stacks and thus increase the cost. In addition, these digital bus architectures have their own uncertainty because of node-to-node delay, which cannot be accepted by applications which are easily influenced by delays such as compartment active noise elimination, etc.

Automobile audio bus® (A2B®) is an innovative technology aiming at application development launched by ADI. It has been proven that this technology can reduce up to 75% of the cable weight and can also provide high fidelity digital audio. Aiming at optimizing audio applications, A2B can provide excellent audio quality compared with analog audio buses, of which the total system cost is far below the existing digital bus standards.

From the perspective of implementation, A2B is a kind of single master and multiple slave line topology. It utilizes a daisy chain supporting 8 slave nodes at most on an unshielded twisted pair, so it doesn’t need redundant cables required by some competitive technologies. Depending on this kind of daisy chain ability, the bus distance of A2B can reach up to 40m, and the longest distance between single nodes can reach 15m. Replacing the ring topology with a line topology is a key factor of A2B technology, which is crucial for the overall system's integrity and robustness. If a link in the A2B daisy chain is influenced, the entire network won’t collapse, and only the downstream connection nodes will be influenced by the failure. This way, the specific built-in diagnostic function of A2B technology can isolate the source and the cause of failure.

A2B is a kind of single master and multiple slave system, of which the transceiver in the master controller is used for the master. This master transceiver can generate clock, synchronization, and framing signals for all slave nodes, and can also realize configuration and back-reading through control bus (I2C) programmes. The A2B data stream is embedded in the extension version of this control bus which can directly access the register and status information of the slave transceivers and provide over distance I2C-to-I2C communication.

Numerous mature and emerging markets will benefit from the high efficiency provided by A2B technology. The target applications include audio ECU connectivity (vehicular audio systems, amplifiers, and smart antennas), which is available for the microphone array including the speakerphone, automatic speech recognition, in-car communication, and supports active noise elimination and active speaker.

Through the multichannel I2S/TDM interface, the AD2428 A2B transceiver launched by ADI can be directly connected to general-purpose digital signal processors (DSP), field-programmable gate arrays (FPGA), application-specific integrated circuits (ASIC), microphones, analog-to-digital converters (ADC), digital-to-analog converters (DAC), and codecs. It also provides a PDM interface which can be directly connected with up to 4 PDM digital microphones.

AD2428 transceivers also support A2B bus powering features, of which the master node can provide the voltage and current for the slave nodes through the same twisted-pair cable used for the communication link and connected with the daisy chain. Thus the bus doesn’t need to supply power for the slave nodes.

AD2428 transceivers support all the A2B bus features above and use SigmaStudio® graphical software tools to conduct configuration, which is configured to provide an I2C port and 8-bit to 32-bit multichannel I2S/TDM interface for the A2B bus master (supporting as many as 10 slaves), support I2S/TDM programmable data rate in 32 upstream and 32 downstream channels, support a PDM interface and 4 high dynamic range microphone inputs with programmable sampling rates, carry out 24-bit PCM demodulation, support the receiving of I2S data from the node configured with 4 PDM microphones, provide a unique ID register for each transceiver, support crossover or straight-through cabling, and provide programmable settings to optimize EMC performance.

In order to assist customers with developing their A2B system, ADI has also launched multiple evaluation kits. Because the A2B system can adopt multiple configurations, customers can verify the system operation with the combined use of various evaluation platforms. The evaluation kit is embedded with an AD2428W automobile audio bus A2B transceiver which supports an A2B master and/or slave operation according to the requirements, supports local or bus power supply in terms of the configuration, and supports or does not support an I2S/TDM interface, 0-4 PDM microphones, and other combinations.


Featured Product

Analog Devices AD2428WCCSZ01 Bus Transceiver


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