A2B® was developed for use in unshielded enclosures with unshielded cable in an environment where emissions are highly regulated by the automotive manufacturers to ensure that sensitive RF electronics are not unintentionally degraded by unintended emitters.  Digital systems with fast risetimes are notorious for generating radiated harmonics out to 20 or more times the fundamental, in this case putting that noise up around a few GHz with the potential to interfere with a wide range of automotive electronics.

At lower frequency (typically under 10 MHz) conducted emissions can be a problem. While the signalling rate of the A2B protocol is high (approx 100 MHz) data is packetized and many of the burst of data happen at the audio sample rate (48 kHz) and sub-multiples of that.  These lower frequency components can find their way into a range of devices through either power or signal connections.  Again in an automotive environment there are multiple sensitive sensor systems to contend with, as well as an audio system where noise pickup would be detrimental to the user experience.

There are a range of A2B applications that do not have these concerns: the system may operate totally inside of a metalic enclosure, or wiring configurations may be shielded and only need to meet less stringent FCC/CE type requirements.  Or the use of a ferrite clamp to reduce common mode noise on cables would be acceptable where as in an automotive environment weight minimization is critical.

There are large number of components in the passive network used on the LVDS upstream and downstream connections for automotive applications.  Other applications may not need those components.  However there would be time and expense to create new PCB designs and evaluate them for their performance.

A simpler and faster way is to use the Clockworks' A2B module as a standardized test bed.  The PCB design was created to make it intentionally easy to modify compared to other evaluation boards available from Analog Devices.  The Clockworks board has all components on one side, making probing easy.  All components are 0603 or larger, simplifying removal or substitution of components.

The next illustration highlight components in the passive network for the A2B bus.

There may also be cases where measurement of the frequency/phase characteristics of the passive network would be desired, but without any other components. Rather than strip down a standard module Clockworks can supply blank boards. While there will be obvious dependencies of the particular layout used on the module, experimentation can help gain insight in to application issues.

Another area for removing components to examine the effect on operation is for the phantom power circuit.  Many systems will have only locally powered nodes and there's no need for a phantom supply on an upstream node.

The actual cost savings from creating a design with less components may come not from the cost of the components but the assembly costs associated with placing the parts on the board.  Understanding what can be removed for specific applications without compromising the A2B system integrity is simplified with easy to modify hardware.

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