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TPA2016D2: Poor reception with Si4731 AM/FM receiver IC

Mike Molt
Prodigy 70 points
Part Number: TPA2016D2

I've designed and built an AM/FM receiver and amplifier board, but have noticed that the FM reception is poor for all but the strongest FM broadcasts.  Compared to other FM radios in my house, the reception is not very good.  I'm new to this, but I suspect the class D amplifier is the culprit.  What can be done to fix this?  Should I switch to a class A/B amplifier IC?

  • 0
    TI__Mastermind 20085 points
    Hi Mike,

    The audio amplifier just amplifies the input signal, so I consider that the culprit could be the AM/FM circuit.
    Perhaps, the FM signal is lower and this produces the reception problem. Have you measured the input and output signal of the amplifier when it is receiving AM and FM? If no, you could measure them in order to verify if the FM signal is lower than AM signal.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • 0 in reply to José Luis
    Prodigy 70 points

    Jose, I'm afraid I don't have the ability to make those measurements. The reason I suspected the amplifier, is that from just "Googling", it seems like many experience fm reception issues when using a class D amplifier. I don't completely understand it, but from what I've read, maybe the high frequency switching, inherent to the highly efficient class D amplifier is in the same range as FM frequencies (88~108MHz).

    I should add, this is a reception issue, not a sound quality issue.  Simply put, I'm not able to receive stations that are easily received on the other FM radios in my house.  When the amp is off, I'm able to receive the FM stations cannot with the amp on.  I'm able to check FM signal strength via i2c communication with the Si4731.

  • 0 in reply to José Luis
    Prodigy 70 points

    More research points me in the direction of adding ferrite beads to the amp outputs, to filter high frequency emissions.  How would I go about sizing the ferrite bead?  Or generally is there a better approach?

  • 0
    Prodigy 70 points
    Jose,

    Thank you for your response. I am currently not using any sort of filter. The amplifier documentation suggests it's a filterless design, so I started that way on the first revision.

    I'm not sure I understand your response when you state "surely the filter is attenuated the FM frequencies". Any ferrite bead filter will be on the output side of the amplifier, and not connected to the radio receiver in anyway. As I understand it, the ferrite bead is used to filter out the high frequency noise generated by the class D amplifier. Again, I'm talking about FM reception.

    Also as previously stated, FM reception is improved when the class D amplifier is turned off.
  • 0 in reply to Mike Molt
    TI__Mastermind 20085 points

    Hi Mike,

    Sorry for the delay.
    You could add a Ferrite Bead Filter as this filter avoids Electro-Magnetic interference (EMI) and this should fix your problem.
    You can refer User's guide of the EVM to find inductors bead and capacitors that could use for your application.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer

  • 0 in reply to Mike Molt
    TI__Mastermind 20085 points
    Hi Mike,

    I haven't heard back from you. I am assuming that you were able to solve your problem. If not, just respond to this message or create a new post if this was locked due to time-out.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer