Innovative digital bus architecture reduces audio system costs

By Ken Waurin, marketing manager at Analog Devices C

ar manufacturers strive to make future generations of vehicles safer, smarter, and more fuel efficient than

their predecessors. To accomplish this, electronic systems continue to increase in number and complexity as more electronic control units (ECUs) are deployed in the vehicle, enabling new features and capabilities such as smart radio connectivity, road noise cancellation (RNC), personal audio zones (PAZ), in-car communications (ICC), and autonomous driving. As the number of ECUs increases, so does the weight and cost of the required cabling harnesses that provide connectivity between the various ECUs. This added weight, in turn, decreases the fuel efficiency of the vehicle, much to the chagrin of car manufacturers. Car manufacturers must balance

their desire to deliver advanced, feature-rich infotainment systems with

the need to comply with government imposed fuel efficiency standards. Reducing the weight of existing cable harnesses can lead to significant improvements in fuel efficiency.

Current landscape Traditionally, automotive audio ECUs have been connected by either individual analog cables or existing digital bus architectures—both of which present limitations, inefficiencies, and unnecessary expenses. Car audio systems that use analog wiring require dedicated, expensive, shielded cables for each audio signal or channel. In today’s premium audio systems, by supporting multichannel (5.1 or 7.1) Dolby or DTS decoding, the number of required cables rapidly increases. Additionally, the required analog-to-digital converters (ADCs) and digital-to-analog converters

(DACs) increase total system cost while introducing potential areas of audio performance degradation. Digital bus standards such as MOST or

Ethernet AVB have been widely adopted in current generation infotainment systems because they greatly simplify the wiring complexities associated with analog implementations. However, the added performance and flexibility of MOST and Ethernet. AVB carry the added cost of expensive

microcontrollers to manage their associated software protocol stacks. Additionally, these digital bus architectures are inherently nondeterministic with variable system delays from node to node. This fundamental flaw in existing digital bus architectures is not acceptable for latency-sensitive speech and voice-based applications, such as ANC/RNC and ICC.

Introducing the automotive audio bus The Automotive Audio Bus (or A2B) is an innovative and application tuned technology from Analog Devices that is

proven to reduce the weight of cable harnesses by up to 75 per cent while delivering high fidelity digital audio. A2B is optimized for audio applications delivering superior audio quality relative to analog connectivity at significantly lower total system cost than existing digital bus standards. In its simplest form, A2B is a high bandwidth (50 Mbps) digital bus capable of transporting I2S audio and I2C control data together with clock and power using a single, 2-wire, unshielded, twisted pair cable over significant distances - up to 15m between nodes and 40m over the entire daisy chain.

Automotive audio bus basics From an implementation standpoint, A2B is a single master, multiple slave line topology. The AD2428W, together with two feature-reduced, lower cost derivatives—AD2427W and AD2426W— comprise the latest family of pin- compatible, enhanced A2B transceivers. These latest product introductions support the daisy-chaining of a single master, plus up to 10 slave nodes, which represents a 20 per cent increase relative to first generation A2B offerings, as seen in Figure 1. This daisy-chaining capability allows a maximum A2B distance of up to 40 m, with up to 15 m supported between individual nodes. Using a line topology instead of a ring topology is an important element of the A2B technology related to overall system integrity and robustness. If one connection of the A2B daisy-chain is compromised, the entire network does not collapse. Only those nodes downstream from the faulty connection are impacted by the failure, while the embedded diagnostics inherent to the A2B technology are able to isolate the source of the failure, signaling an interrupt to initiate corrective action. The A2B master-slave line topology is

inherently efficient when compared to existing digital bus architectures. After a simple bus discovery process, zero additional processor intervention is required to manage normal bus operation. As an

Figure 1. A2B automotive audio transceiver functional block diagram Continued on page 20 Components in Electronics May 2019 19

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