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LMH5401: optimal resistor values for the input circuit

Michael T Schneider
Expert 3780 points
Part Number: LMH5401
Other Parts Discussed in Thread: ADC12DJ3200QML-SP,

Team, 

We are looking for a recommendation on the optimal resistor values for the LMH5401-SP input circuit for the 0.707 V/V, 1 V/V and 10 V/V gain configurations. Per the earlier correspondence on the subject, recorded below, the RF input power is controlled and we select it. We appreciate your feedback.

Gv = 1 V/V per the spreadsheet.  ADC needs 0.8Vpp-diff which is 1.6Vpp-diff at AMPOUT (with 50ohm match as shown).   With Gv=1V/V, Vin=1.6Vpp-se.  Want to confirm this signal level is what is expected at LMH5401-SP input.  Equates to -9dBm power gain.  We can recommend an optimal circuit if we know the max input voltage to LMH5401-SP and confirm max input to ADC needed is 0.8Vpp-diff.

 

 

  • 0
    Guru 48395 points

    Morning Michael,

    Before too much work, why are you taking a 6dB matching loss at the output. That is normally not necessary in the FDA to ADC interface - I know a lot of filter tools set up for that, but you are wasting swing and optimum power transfer is not the issue, the ADC converts voltage, not power. If you want a low insertion loss filter, tell me the filter parameters. 

  • 0 in reply to Michael Steffes
    TI__Expert 3780 points

    The LMH5401-SP is the only space grade HSA that can replace balun in our system. we have to work with it. we only need about 6 bits ENOB out of teh ADC12DJ3200QML-SP device for now. 

    for future designs with the ADC12DJ5200QML-SP we will need to move back to a passive balun for space grade solutions. 

    just looking for some help in our current design. 

  • 0 in reply to Michael T Schneider
    Guru 48395 points

    I thought I had alreaty replied to this,but that appears to have not made it - 

    Well if you trying to replace a balun,can you show your current circuit -the active balun ckt with the LMH5401 might be ideal. 

    Have you seen that presentation I was doing in the Phoenix space accounts on this active balun design flow - done right, it is very low noise figure.

    Replacing a balun? AC coupled is ok I am guessing, then normally a single ended 50ohm input impedance to diff out of the LMH5401

    Lot of flexibility on that output interface, usually with some filtering but rarely with 6dB insertion loss unless transmitting some distance. 

  • 0 in reply to Michael Steffes
    Guru 48395 points

    Well Michael Schneider, 

    You perhaps have located this slide deck, it does tell you how to do this - if not, email me and I will send it over (email in profile) assuming I can find it.

  • 0 in reply to Michael Steffes
    TI__Genius 15555 points

    Hello,

    It seems like this was taken offline so we will close the thread. Please reply if further discussion is needed.

    Best,

    Hasan Babiker