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DS90UB914A CML out trigger point

Toshi
Expert 1780 points
Hi TI, What is the trigger point of the Eh,Ew measurement (CML MONITOR OUTPUT DRIVER SPECIFICATIONS), PCLK out of ‘UB914? PCLKIN of ‘UB913? or CDR in Scope ? Also If use a CDR in scope, please let me know a filter frequency of the CDR?
  • 0
    TI__Expert 5210 points
    Hello Toshi,

    The trigger point on the CMLOUT eye can either be the signal itself or one can choose to trigger on the PCLK input or output instead (typically the output since this will likely have less jitter). Both will yield approximately the same result. It is recommended to set the trigger at 50% of the amplitude of the signal you choose.

    To see the correct amplitude eye coming out of the CMLOUT driver on the 914A (TEST +/- pins), one will need to perform oscilloscope math: (CMLOUT[+] signal) - (CMLOUT[-] signal). This is because the CMLOUT driver is differential in nature. Therefore, the trigger point (50%) for the final CMLOUT signal here would be 0V. To trigger on either the + signal or the - signal, the trigger point will be either VOD/2 or -VOD/2 respectively.

    -Sean