• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 11 subscribers
  • Views 894 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TRF370417 - Lack of output power / bad return loss

Stefan Artz
Prodigy 20 points
Other Parts Discussed in Thread: TRF370417

Hello,


I wanna use the TRF370417 at 5.8 GHz RF. I made an eval board with two baluns for the inputs I & Q. The inputs for the LO I made like on the evaluation board from TI. The RF output is also like on the evaluation board (all signal traces are 50 Ohm grounded cpw, coupling capacitance, SMA, FR4).

I first measured the return loss of the output (according to datasheet: return loss = 15 dB over 0.05 - 6 GHz). I measured via NWA a return loss of about 2-3 dB at 5.8 GHz.

The Output power is measured like in SLWA056 described. It is about 3.7 dB less than according to  the datasheet (Example: @2.14 GHz and 0.1 Vrms: Output power = -3.4 dB according datasheet, but I measure @2.14 GHz and 0.1 Vrms: Output power = -7.1 dB).


I/Q signal frequency in all cases: f = 50 kHz

Why is the return loss not about 15 dB when the TRF370417 does not need any external components and the traces are 50 Ohm designed?


Thanks for your help.


Best regard,

Stefan

  • 0
    TI__Mastermind 18095 points
    The return loss of the TRF370417 is actually less than 10 dB per design due to the broadband active D2S circuit. Return loss degrades even further above 4-GHz to something around 5 dB. Close to 6-GHz your measurements are likely accurate.

    The 15-dB return loss in the D/S refers to the LO port. Some frequencies provide output RL in the tables. Other frequencies, particularly the higher frequencies, the RL is not specified. Looking at the figure 2 which plots output power vs. frequency, the output power is around -7 dBm at your frequency of 5.8 GHz.

    Even though the RL is not great, it is still best to terminate with a broadband 50 ohm load. Conjugate matching is not recommended as it distorts the linearity performance. Adding a small resistive attenuator/pad on the output can help interfacing the modulator to the next device in the line-up.

    --RJH
  • 0 in reply to RJ Hopper
    Prodigy 20 points

    Thank you for your answer and your help.

    Best regards,

    Stefan Artz