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Is logarithmic RF detector ADL5513 a fully differential design ?


I have a question regarding the logarithmic RF detector ADL5513. In the datasheet
( on page 13 is written that it is a fully
differential design but on page 14 under section INPUT SIGNAL COUPLING is written : “The RF input (INHI) is single-ended and
must be ac-coupled. INLO (input common) should be ac-coupled to ground.” . Could you tell me now if this log detector input
is differential or do I need to ground INLO? I need to measure the rf power of a differential signal generate by the Transimpedance Amplifier ADN2880. If the above ADL5513 is not
differential, then what about AD8318 and AD8313 or do you have other recommendations? It should have a high dynamic range and
wide bandwidth like ADL5513. Thank you and best regards Sebastian Blank
  • Hello Sebastian,

    ADL5513 input is differential, but typically there is little-to-no performance benefit of using differential drive, compared to single-ended drive. Consequently, the ADL5513 applications tend to focus on the single-ended drive, which is better suited to existing lab equipment signal sources. 

    Differential drive should work well also, but notice there is no ADL5513 performance specification for CMRR. If this is important, you would have to test for yourself, or use another diff2SE solution. 

    ADL5513 always requires AC coupling of both inputs, as depicted by C1 & C2 of Figure 25, Basic Connections.   -Bruce H.