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Original question:

AFE7950: AFE7950 9.6GHz RF Single Ended to Differential Matching

AFE7950: Matching circuit for differential input (RX)

Felipe Cerqueira Lyra
Prodigy 10 points
Part Number: AFE7950

Tool/software:

 Hi,

I have some questions regarding the matching network and the S-parameters of the AFE7950.

Regarding the S-parameters:

    1.What was the setup used to measure the S-parameters?

    2.Is it normalized to 100R or 50R?

    3.In the "simulation" folder, only the differential mode S-parameter, Sdd11 is present. Is it possible to add the remaining parameters, Scd11 Sdc11 Scc11?

    4.Was the Sdd11 measured with or without the matching network?

Regarding the matching network

    1.Does the suggested values, present in the "AFE79xx_Matching.xlsx" file,  take into account the parasitic capacitance and inductance of the lumped elements?

    2.What is the reason for different circuits for the odd and even RX channels?

    3.Since the signal is already on a 100R differential pair, and the port is 100R differential (according to the datasheet), what is the need for the matching network?

  • 0
    TI__Expert 5035 points

    Hi Felipe,

    Please see the replies below:

    1. What was the setup used to measure the S-parameters?
      1. This was done using a board with only traces on the RX, TX, FB and Fref inputs/outputs. Then the measurements were taken with a VNA along with a test fixture that had the same traces as the inputs/outputs to de-embed the traces from the measurement.
    2. Is it normalized to 100R or 50R?
      1. RX/FB is normalized to 100Ohms dif. Tx is 50ohm output differential termination impedance for the AFE795x family. And 100ohm output differential termination impedance for the AFE790x family.
    3. In the "simulation" folder, only the differential mode S-parameter, Sdd11 is present. Is it possible to add the remaining parameters, Scd11 Sdc11 Scc11?
      1. Only the Sdd11s were taken.
    4. Was the Sdd11 measured with or without the matching network?
      1. Without matching network. Refer to Q1.
    5. Does the suggested values, present in the "AFE79xx_Matching.xlsx" file,  take into account the parasitic capacitance and inductance of the lumped elements?
      1. The values in the "AFE79xx_Matching.xlsx" file are tested on the EVM. On a custom board the values might have to be adjusted to compensate for differences in layout and substrate.
    6. What is the reason for different circuits for the odd and even RX channels?
      1. The reason is due to different routing. Both in the EVM and in the substrate.
    7. Since the signal is already on a 100R differential pair, and the port is 100R differential (according to the datasheet), what is the need for the matching network?
      1. Matching networks are used for multiple reasons. In many RF circuits the source and the input port will not necessarily have a perfect impedance. And the transmission through the board will also cause a mismatch. Matching networks help counteract these effects. Matching networks can also help to improve the bandwidth of the system.

    Let me know if this answers your question.

    Best,

    Camilo