ALLGEMEINE BESCHREIBUNG

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, daisychained 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.

 

A²B BUS FEATURES

Line topology Single main node, up to 16 subordinate nodes Up to 15 m between nodes and up to 80 m overall cable Length
Communication over distance Synchronous data Multichannel I²S/TDM to I²S/TDM Synchronous clock, phase aligned in all nodes Low latency node to node communication Control and status information I²C to I²C GPIO and interrupt
Bus power or local power subordinate nodes
Configurable with SigmaStudio/SigmaStudio+ graphical software tool
AEC-Q100 qualifiziert für Automobilanwendungen

 

A²B TRANSCEIVER FEATURES

Configurable A²B bus main node or subordinate node
Programmable via I²C interface 8-bit to 32-bit multichannel I²S/TDM interface Programmable I²S/TDM data rate Up to 32 upstream and 32 downstream channels PDM interface Programmable PDM clock rate Up to 4 high dynamic range microphone inputs
Simultaneous reception of I²S data with up to 4 PDM microphones
Unique ID register for each transceiver
Crossover or straight-through cabling
Programmable settings to optimize EMC performance

 

ANWENDUNGEN

Audio communication link
Microphone arrays Beamforming Hands free and in car communication
Active and road noise cancellation
Audio/video conferencing systems

 

I²S Reduced Rate

Subordinate transceivers can run the I²S/TDM/PDM interface at a reduced rate frequency, with respect to the superframe rate. The reduced rate frequency is derived by dividing the superframe rate from a programmable set of values. Different subordinate nodes can be configured to run at different reduced I²S/TDM rates.
The transceiver provides an option for a processor to track the full rate audio frame, which contains new reduced rate samples. The IO7 pin can be used as a strobe, and the direction can be configured as an input or output.

 

CLOCK SUSTAIN STATE

In the clock sustain state, audio signals of locally powered subordinate nodes are attenuated in the event of lost bus communication. When the bus loses communication and a reliable clock cannot be recovered by the subordinate node, the subordinate node transceiver enters the sustain state and, if enabled, signals this event to a GPIO pin.
In the clock sustain state, the phase-locked loop (PLL) of the subordinate node transceiver continues to run for 1024 SYNC periods, while attenuating the I²S DTX0 to DTX1 data. After the 1024 SYNC periods, the subordinate node transceiver resets and reenters the power-up state.