Testing the MOST150 Coax Physical Layer: Page 3 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.
a 50 Ohm transmitter that can be adjusted for different predefined rise and fall times from 700ps, 1000ps and 1400ps. The shaper also allows setting the steady-state amplitude in a range from 300mV up to 420mV. Each of the three different cable models is attached to a separate signal shaper to provide seamless integration.

Figure 2: Block Diagram of MTCM. For higher resolution click here


Design requirements for each cable model are shown in Table 1. Cable Model “Low” describes a short test cable with fast rise and fall times and maximum steady-state amplitude. Cable Model “Mid” is intended to cover a typical cable connection and cable model “High” is built to simulate the worst-case channel with slow rise and fall times of 1400ps and minimum steady-state amplitude of 300mV. Figure 3 displays a comparison of the three implemented cables models.

Table 1: Design Requirements


Figure 3: Comparison of the three implemented Cable Models



The outgoing signal of the particular cable models is routed to the output connection of the MTCM (In-Out Duplex, Out Simplex) via a Directional Coupler element. In a duplex operation, signals are distributed over one single cable in both directions. Therefore, the directional coupler is used to split the incoming from the outgoing signal. The incoming signal is forwarded to a Measurement Amplifier which generates an output signal for analysis by an oscilloscope and, simultaneously, providing the needed return signal for the PhLSTT to close the ring network for data consistency testing. The gain of the Measurement Amplifier can be turned to low or high amplification to compensate the loss of the internal directional coupler.


For the simplex setup, the directional coupler is still part of the outgoing channel to maintain identical channel characteristics for both simplex and duplex. However, the return path is established by an additional input connector (IN Simplex) and uses the measurement amplifier to create signals for

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