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TRF7962A: The large harmonic of TRF7962A

Nomo
Guru 16800 points
Part Number: TRF7962A

Hello,

Now, we are testing the leakage power (EMC test) of TRF7962A (on our custom board) in the 200mW output mode.
Because of the test, the leakage power level (200MHz - 800MHz) is higher than the level defined by regulation due to harmonic.
Could you confirm the following questions?

1.Do you know the way to remove the harmonic (200MHz - 800MHz)?

2.We are considering inserting capacitors to pin 5 (TX_OUT) and implementing LPF to remove the harmonic.
  Could you advise us how large capacitor can connect to pin 5?
  Also, is there any important point to connect the capacitor?

Of course, we are referring the reference design and copying the constant value.
The output wave from TRF7962A is following.
We can see the harmonic from 200MHz to 800MHz.

Best Regards,
Nomo

  • 0
    TI__Guru*** 129700 points

    Hello Nomo-san,

    The device operates at 13.56MHz, I am surprised that it would appear to be radiating notable energy at 200-800MHz. Also many of the frequency spikes do not even align with a harmonic from the 13.56MHz signal.

    If it only occurs when the RF field is on, then chances are it's related to the power topology as the device draws significantly more current when the RF field is being output.

    P.S. a large cap on TX_OUT would ruin the TRF7962A match network and it would need to be redesigned from scratch. That isn't a solution that should be considered at all.

    Is this test measuring on the PCB or in the air? I presume in the air. Also are there any other radio devices on the board?

    We have done many EMC tests and had no issues passing with the device, so at worst it is poor system design.

  • 0 in reply to Ralph Jacobi
    Guru 16800 points

    Hello Ralph-san,

    Thank you for your comment.
    We'll check our system design.
    If we had additional question, we'll post another thread.

    Best Regards,
    Nomo