Application Note for MOST150 Coax Physical Standard is Available

This MOST150 coax physical standard complements the existing MOST150 optical physical layer in the infotainment domain, especially for OEMs who have strong preferences for an electrical physical layer. In addition, this new standard opens the way for using MOST in other vehicle domains. For example, it fits well in the driver assistance domain, as this physical layer is able to provide bi-directional communication and power supply on a single coaxial cable.

The test board used is a series of distinct functional blocks: transmitters, cable transmission line (TL) models, multiplexer, noise adder (for emulation of reflections), directional splitter and amplifier for the return signal.

Several options can be chosen by 24 DIP switches or with a remote control through a USB port of a PC. The cable model was verified in the time and frequency domain with a cable having the same attenuation curve as the worst case curve in the cPHY MOST150 Specification. Three transmission line models can be tested. A very short one, and two of maximum length, one of which is close to ideal attenuation at that length, and one that has maximal deviation according to the cPHY spec. Worst case reflections (return-loss) that can occur in the cable itself generate cross-talk in full-duplex mode.
This can be emulated for said three transmission line models. On top of that, the worst case reflection at the receiving side, also generating cross-talk, can be added to generate the absolute combination of worst case conditions, and evaluate the proper operation of the cPHY receiver under test.