Differential or Single Ended Impedance?

Discussion in 'Wireless & RF Design' started by Rogue 52, Jul 7, 2009.

  1. Rogue 52

    Thread Starter New Member

    Mar 12, 2008
    1
    0
    I've been working with the following IQ Modulator: http://www.hittite.com/content/documents/data_sheet/hmc496lp3.pdf

    In any case, the data sheet states "Signal lines should have 50 ohm impedance...". All input lines are differential on the part. Does this 50 ohm impedance mean single ended? This is what I assume but it never states this explicitly. I'm wondering if I need to divide the amount by two to obtain the actual single ended input impedance.
     
  2. Ataleph

    Active Member

    Apr 20, 2009
    31
    0
    Hi Rogue 52,
    Your assumption is quite correct. But "it never states this explicitly" for the following reason. When they talk about "Signal lines", the transmition line impedance is meant, i.e. it is not about single-ended or differential but about an impedance of transmition line which a signal "sees" while passing through this line. That is Z0=V/I, where V is a voltage wave proceeding at each point of transmition line and I is a current wave proceeding at each point of transmition line.
    In practice this is an impedance between each channel (p or n) and ground, therefore you can assume it is single-ended impedance.
    Hope this helps...
     
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