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Original question:

DS125DF410: Any upper limit to the EOM_TIMER_THRx setting?

DS125DF410: EOM gain/attenuation manual adjustment and readback

child sun
Prodigy 190 points
Part Number: DS125DF410

We are using the EOM function to gauge the quality of the incoming signals. We noticed that the EOM function adjusts its gain/attenuation automatically to maintain a constant output amplitude for eye measurements. There are two questions:

1. Can the gain/attenuation value be read out through register access?

2. Can the gain/attenuation value be set manually (so as to disable the auto adjustment function)?

Thanks.

Child

  • 0
    TI__Mastermind 21655 points

    Hi Child,

    By output amplitude for eye measurements do you mean EOM vertical range? This can be read in register 0x29[6:5]. We recommend manually setting the vertical range with register 0x11[7:6].

    What testing have you done to find that EOM adjusts its gain/attenuation? It would be helpful for me to better understand what you mean by gain/attenuation.

    Best,

    Lucas

  • 0 in reply to Lucas Wolter
    Prodigy 190 points

    Lucas,

    I was not talking about the EOM vertical range/window that we can set or read out through reg 0x11 and 0x29, but the actual attenuation/gain level that the EOM block imposes on the incoming signal. 

    I noticed the behavior through the following experiment:

    1. A signal of fixed amplitude is created at the source and injected to the EOM block.

    2. EOM vertical value (i.e. VEO) can be read out through the eye measurement function.

    3. Then we add external attenuation to the signal path and notice that the VEO value stays almost unchanged (vs. becoming smaller in amplitude) - until the external attenuation has become very large (say, >15dB).

    Is there a way to set and/or read the internal EOM attenuation/gain level?

    Thanks.

    Child

  • 0 in reply to child sun
    TI__Mastermind 21655 points

    Hi Child,

    The VEO value is being scaled to the vertical range set in register 0x11[7:6]. Unfortunately, as far as I can tell it's not possible to read how much attenuation/gain is being applied to meet this vertical range. However, this can be disabled by setting register 0x2C[6] = 0 to get VEO values based on actual input signal amplitude.

    Best,

    Lucas