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DS90UB954-Q1: Bandwidth, Design Margins and Attenuation questions

Mark Pearson
Genius 12705 points
Part Number: DS90UB954-Q1
Other Parts Discussed in Thread: DS90UB953-Q1EVM,

I am asking the following questions for one of my customers:

I have been using the DS90UB954-Q1EVM and DS90UB953-Q1EVM boards to evaluate several coax cables.

1. The datasheets for the FPD III parts is very vague as to what the required attenuation budget is. Do you have any graphs that show the allowable attenuation vs frequency for this link? (such as a minimum S21 magnitude vs frequency plot) 

 

2. What is the actual bandwidth requirements of the FPD III link? In the DS90UB953 datasheet, there is a paragraph in section 8.1 that outlines the forward channel. The frequencies called out do not make sense, since the only eye diagram listed in the datasheet shows that the edge transition time of the forward channel is 65ps, which would lead me to believe that 15GHz is the critical frequency. Is there more detailed information available on what the critical link frequencies are?

See Section 8.1 'Application Information' (DS90UB954 datasheet) and the eye diagram from section 6.8, figure 3.

3. I have been using TI's Analog LaunchPad tool with the  DS90UB954-Q1EVM evaluation board. In the scripting folder for the 954, there is a script for doing link margin analysis (C:\Program Files (x86)\Texas Instruments\Analog LaunchPAD v1.57.0010\PreDefScripts\DS90UB954\ub954_margin_analysis_script). This script appears to be sweeping several link parameters to determine if a link can be maintained, and it produces a CSV file with the results. My question is, what is the parameters that it is sweeping? The columns are labeled as "SP" and the rows as "EQ", and I no mention of what the contents of the cells mean (I thought it was a 0 or a 1 for fail / pass, but I have seen a 0.3 appear once).

4. Related to question 3, how do I interpret results from the margin analysis tool? As in, how does the margin analysis help me determine that my selected cable will have enough margin to work in the field? I have attached the results on one of my cables for reference.

molex_1000660054_ub954sfeq_test.xlsx

Thank you for your support.

 

  • 0
    TI__Expert 4555 points

    Hi Mark,

    1. Sent offline to TI email.

    2. The bandwidth requirements depend on the mode that you are using for the 953. It will be the backchannel rate up to the Nyquist frequency (2GHz for a 4Gbps line rate). Please see Table 6 in the DS90UB953 Datasheet. The max bandwidth for the 953 is 12.5MHz - 2GHz.

    3. SP stands for strobe position, and sweeps from a range 0-14. The EQ is also swept from a range 0-14, and the margin analysis tool will display a 1 in green for the sweep setting that was able to lock 10/10 times. For cases like 0.3, it means that with that specific sweep setting, the 954 was able to achieve lock 3/10 times.

    4. The way the AEQ works is that it will automatically select the 1st SP/EQ parameter setting that is able to pass the locking test threshold (10/10 locks). You can use the margin analysis tool to select an SP/EQ parameter setting that has more margin so that it is less likely you lose lock. For example with the file that you attached, the 954 would use the EQ setting = 9 and SP = 8 for the AEQ. This would not give much margin for the cable and it is likely the 954 will lose lock. By using the margin analysis tool, we can select a setting with a larger margin, for example EQ = 12 and SP = 9.

    Regards,

    Jonny

    Training on FPD-Link Serializer Deserializer devices and system: https://training.ti.com/fpd-link-learning-center

    More information on IVI or ADAS FPD-Link products: http://www.ti.com/interface/fpd-link-serdes/overview.html