Testing the MOST150 Coax Physical Layer: Page 2 of 4

June 09, 2016 //By Jörg Angstenberger and Frederic Garraud, Ruetz System Solutions
Testing the MOST150 Coax Physical Layer
New challenges and demands for Physical Layer Testing occur with the introduction of an additional Physical Layer for MOST150, based on 50 Ohm coax connections for simplex and duplex transmission.
MOST150 cPHY Compliance Verification Procedure [2], utilizes some of the functions of the PhLSTT but requires some additional features that have to be realized by an external extension to the PhLSTT. This extension is called MTCM and is described in MOST150 Tester Cable Model [3].  

MTCM for cPHY – Extension Tool for Physical Layer Stress Test Tool

The main purpose of the MTCM is to emulate a transfer function, which represents a coax interconnect on a MOST150 stress pattern. The MOST150 pattern is created by the PhLSTT and feeds the DUT. Three different cable models are defined in order to simulate a transmission channel, which covers typical use cases in the car. A transmitter with adjustable rise and fall times drives these cable models, which represent a short, mid and long transmission line. An integrated coupler splits the incoming signal from the DUT into a path for oscilloscope measurements and a return path to the PhLSTT. One of the advantages of the cPHY technology, in terms of measuring MOST signals, is the fact that the transmission system is terminated by 50 Ohms and therefore can be directly attached to an oscilloscope without an additional probe. The MCTM is able to provide a test solution for simplex as well as for duplex operations. For duplex operations, an additional noise adder option is available when an external signal source is connected to the MTCM.

Inside the MTCM

The block diagram of the MTCM is shown in Figure 2. The MTCM is designed to work with various input signals, either single-ended or differential signals, as provided by SMA or HSD connectors. (HSD allow direct connection to the PhLSTT.) Element Switch Input Selection in the block diagram selects a dedicated input and routes the signal to the required cable model channel. Each cable model channel consists of a S ignal Shaper element and the Cable Model itself. The signal shaper is based on

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