Analog Devices

The Automotive Audio Bus®(A2B®) is an innovative technology that reduces system cost, weight, and design complexity by distributing audio and control data, together with clock and power over a single, low-cost, unshielded twisted pair cable. The AD2425W is an enhanced A2B transceiver offering an expanded feature set while retaining complete compatibility with existing AD241x devices. The AD2425W is fully configurable supporting both master and slave functionality.The AD2425W is targeted for use in wiring intensive applications where reducing the weight or complexity of existing cable harnesses is a primary system design objective. These applications include Premium Audio Systems, Active Noise Cancellation, and In-Car Communications.ApplicationsAutomotive audio communication linkActive noise cancellationMicrophone arrays for hands free and in car communication

The Automotive Audio Bus (A2B®) provides a multichannel, I2S/TDM link over distances of up to 15 m between nodes. It embeds bidirectional synchronous pulse-code modulation (PCM) data (for example, digital audio), clock, and synchronization signals onto a single differential wire pair. A2B supports a direct point to point connection and allows multiple, daisy-chained nodes at different locations to contribute and/or consume time division multiplexed (TDM) channel content.A2B is a single main node, multiple subordinate node system where the transceiver at the host controller is the main node. The main node generates clock, synchronization, and framing for all subordinate nodes. The main A2B transceiver is programmable over a control port (I2C) for configuration and read back. An extension of the control port protocol is embedded in the A2B data stream, which allows direct access of registers and status information on subordinate transceivers, as well as I2C to I2C communication over distance.The transceiver can connect directly to general-purpose digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), microphones, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and codecs through a multichannel I2S/TDM interface. It also provides a pulse density modulation (PDM) interface for direct connection of up to four PDM digital microphones.Finally, the transceiver also supports an A2B bus powering feature, where the main node supplies voltage and current to the subordinate nodes over the same daisy-chained, twisted pair wire cable as used for the communication link.Table 1. Product Comparison GuideFeatureAD2420AD2426AD2427AD2428AD2429Main node capableNoNoNoYesYesNumber of subordinate nodes discoverable1N/AN/AN/AUp to 10Up to 2Functional TRX blocksA onlyA onlyA + BA + BB onlyI2S/TDM supportNoNoNoYesYesPDM microphone inputs2 mics24 mics4 mics4 mics4 micsMax node to node cable length5 m15 m15 m15 m5 m1N/A means not applicable.2PDM microphones must be connected to the DRX0/IO5 pin.APPLICATIONSAudio communication linkMicrophone arraysBeamformingHands free and in car communicationActive and road noise cancellationAudio/video conferencing systems