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TPA6132A2: TPA6132A2 frequency response have a drop at low frequency

Ben Kuo
Expert 6715 points
Part Number: TPA6132A2

Dear Expert,

My customer use TPA6132A2 for headphone application.

After testing frequency response, they find a drop in low frequency. Did you have any idea what I have to check first?

Schematic and frequency response as below. 

Thanks for your help!

-Ben

  • 0
    TI__Guru* 95385 points
    Hi Ben,

    Some components that form a HPF are the input capacitors. From the schematic I see 1uF and Gain setting is 0dB, so the input impedance is 19.8kohm. The cutoff frequency of the HPF formed by the input coupling capacitors and input impedance is around 8Hz.
    The resistors placed between the amps are 0 ohm?
    It seems that the HPF cutoff frequency is shifted by cascading the amplifiers. Why are the two consecutive amps needed?

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0
    Guru 140200 points
    Hi Ben,

    the pull-up R117 is 0R? So, when turning on Q10 you shirtcircuit V33?

    How did you measure the three curves?

    Kai
  • 0
    Prodigy 10 points
    Hi Ivan:
    1. We used U19 to convert differential signal to single end signal.
    2. We used U20 as the mixer to mix two signal end source. Is this kind of circuit OK for headset application?
    3. Currently, we modified R48, R51, R53, and R56 to 1Kohm resistors.
    4. Original gain of U19 is 0dB. U19 gain will be changed to 6dB when BT handfree is true.
    5. Original gain of U20 is 6dB. U20 gain will be changed to 3dB when BT handfree is true.
    6. We used AP to measure the FR of U20 audio output. AP output Rs value is 20ohm.
    We would like to know if AP output Rs (20ohm) caused cutoff frequency around at 7.9KHz?
    Would you please recommend the resistor value of R48, R51, R53 and R56 in our circuit?
    Would you please also recommend the capacitance value of C78 and C85 in our circuit?
    Best regards,
    Charleson Lin
  • 0 in reply to Charleson Lin
    TI__Guru* 95385 points
    Charleson,

    If R48, R51, R53 and R56 are not 0 ohm, these in addition with C78 and C85 could form a high-pass. Have you tried with different component values for these particular components?

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Expert 6715 points

    All,

    After disable A-weighter, this drop in low frequency can be solved. Thanks for your help.

    -Ben