• I have the answers. --RJH
  • In reply to RJ Hopper:

    Do you mind if I see the answers?
  • In reply to Mahir Arpadan:

    Do you mind if I see the questions?

    I apologize for my tongue-n-cheek responses...I was having a bit of fun since I did not see the questions in the original post.  --RJH

  • In reply to RJ Hopper:

    No problem. Somehow two questions seem to disappear from my post, I noticed that, and I wondered how you had the answers ;)

    Q1: Why are R2,R3,R10,R11 resistor values are 1uf(???) and SMA J3,J4,J9,J10 inputs are terminated with 0.1uF(C31,C32,C8,C9) caps(though they are DNI).

    Q2.1: We would like to drive TRF372017 with a single-ended Quadrature only signal(from a 50 Ohm Arb. Wave. generator). How should i terminate Eval board.

    Q2.2:In the final design we will drive TRF372017 single-endedly and quadrature only with AC coupled FMC144(DAC has 20mA full-scale current source in figure-9) module . Any suggestions terminating TRF372017 for this drive.

    Thanks in advance

  • In reply to Mahir Arpadan:

    Somehow I'm having problems with non existing questions and this time figure lol.

  • In reply to Mahir Arpadan:

    Mahir:

    Q1: The TRF3720 requires a 1.7V common mode voltage. This voltage can come from the BB I/Q source (like from a DAC) or it can be generated internally. The default configuration for the EVM is to generate it internally, thus an AC blocking cap is required. Optionally, the caps can be replaced with resistors and the Vcm can be provided externally.

    There is another option to supply the common mode voltage directly through test points TP14, 15. If this option were to be employed, the series resistors R74, R75, R79, R80 would be placed, the series caps changed to 0 ohms, and optionally place bypass caps C8,C9, C31, C32. Those caps also provide an option for a voltage divider for Vcm to better set the Vcm.

    Q2.1: You can simply terminate the unused port in 50 ohms. Note, you will see a 6 dB drop in gain only driving one of the differential ports.

    Q2.2: I do not recommend operating TRF3720 in single-ended mode due to aforementioned 6 dB drop in gain. I am not exactly sure what the FMC144 reference is related to DACs. I do see a reference design from Abaco that uses a DAC38J84. If this is the card, then you can connect these up differentially with some care on setting the common mode voltage for the DAC. If you are truly using a DAC38J84 as the source, there is another device, the TRF3722, which uses a 0.25V Vcm that can interface directly with that DAC. There are several app notes on the TI web in the product folders of the TRF3720 and TRF3722 that discuss interface with different types of DACs.

    If you must operate single-ended, then you can terminate the unused port in 50 ohms.

    --RJH
  • In reply to RJ Hopper:

    RJ:

    Thank you for your detailed answers. Now I have a better understanding of this device.

    For Q2.2 we will use 4DSP UM047 - FMC144 Module. The device is AC coupled(not DC coupled with DAC38J84) with 4:1 transforemer single-ended outputs. We plan to use DC blocking caps with internal Vcm generation.

    As in your suggestion to use diffferential drive signals, we are evaluating a solution with another 1:4 center tapped transformer to transform single-ended signal to balanced differential signals. Hopfully this will work.

    Best wishes.