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Original question:

LMX2594: RF Output Buffer Pullup

LMX2594: RF Output bias and matching details

Joseph Haas
Prodigy 30 points
Part Number: LMX2594

I am looking for any available design guidance for the RF output for this part.  A previous thread suggested that the pullup inductor be selected with an SRF at or near the operating frequency, but we will be operating across nearly a full octave (7 GHz to 13 GHz).  This suggests a conical inductor, but I'm curious what other options may have been tried (conicals are typically expensive and difficult to assemble).

Also, what design data is available to assist with producing a low-noise matching circuit for the RF output?  We have s2p data for the subsequent amplifier chain, but nothing that speaks to the LMX2594 output impedance over frequency.  Even a Smith chart plot would be welcome.

Cheers

  • 0
    TI__Guru** 109000 points

    Hi Joseph,

    Unfortunately we don't have any modeling for the RF output.

    We have tried several inductor values, a 10nH inductor seems to be the best choice so far. The result is shown in Figure 18 of the datasheet. With this inductor, we can boost the output power for all frequencies. The inductor is Toko LL1005-FH10NU, SRF is 3750MHz. This inductor is obsoleted, but similar inductors are available in the market.