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DS90UB953-Q1: adding DC blocking cap on cable core

Alberto Doronzo
Expert 4830 points
Part Number: DS90UB953-Q1

Hi,

an engineer is asking about the impact of adding a 10-100uF ceramic DC blocking capacitor on the +ve line for FPD-link communication (the core of the coaxial cable).

A part from the slight degradation in the signal edges and amplitude, are there other pitfalls to consider?

Is there any testing that has been done that would show results of such addition?

Thank you!

Regards,

Alberto

  • 0
    TI__Expert 8135 points

    Hello-

    The DC-blocking (or AC-coupling) capacitor together with the internal termination signal poses as a high-pass filter to the FPD-III forward channel and back channel signals.  The high-pass filter helps to filter out any low frequency noise such as the noise introduced by the power-over-coax (PoC) circuit.  If the PoC circuit is used, then the 10-100 uF caps with the internal termination may not be as effective as in filtering the PoC noise as the recommended values (33nF-100nF).

    In addition, the ac-coupling capacitors should be small in size (0402 or smaller package is recommended) to minimize impedance discontinuities in the signal path.  10uF-100uF capacitor would likely have bigger package.

    No testing was done with such a large capacitor values.

    Regards,

    Davor