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TPA3116D2 amplifier

Other Parts Discussed in Thread: TPA3116D2

Dear sir,

am testing TPA3116D2, in Gain 32dB master mode but it gives noise while the input jack is in air. what will be the reason. please suggest me.

input coupling capacitor Ci=5.6uF non polarity capacitor.

thanks

kiran 

  • Hello Kiran,

    1. With 32dB of gain (or scalar gain of 39.8) the input of the amplifier will be particularly susceptible to noise. A floating input will act like a high impedance node, so radiating EMI from computer, florescent lights or other sources can easily couple voltage noise into the amplifier. The higher the gain, the more this noise is amplified at the output. Any analog input amplifier will exhibit this behavior.

    2. When using high gain it is recommended to use a low source impedance so that EMI noise coupling is minimal. Resistor thermal noise (Johnson noise) can also be significant so low impedance will also reduce this effect as well. (ex. adding 100K resistor in series with the input will increase the noise floor significantly).


    Best Regards,
    Matt
  • Hi sir,
    how can i reduce the input impedance?. by changing the value of Ci or else.
    thanks
    kiran
  • Kiran,

    Ci should have a minimal effect on the noise. What you want to reduce, if you can control this in your design, is the output impedance of the audio source you are connecting the amplifier to. The lower this is, the better for noise performance.

    If the amplifier is connected to an external analog audio source that you don't have control over, then self grounding jacks are a good solution. This way when the audio plug is removed, the inputs are automatically grounded.

    Best Regards,
    Matt
  • Hi,


    in reference design manual, they are ignore the input resistance Riin series with Ci, i designed accordingly. is this Ri resistor will reduce the noise, when there is no signal present.


    thanks
    kiran

  • Hi, Kiran

            Yes, changing the input resistance to smaller, the resistor thermal noise will decrease,

          Compare to the Gain=26dB with input impedance=30kohm,  Gain=32dB with input impedance=15kohm,  the resistor thermal noise (input noise) will improve 3dB. But the Gain increased 6dB, so the output noise will increase 3dB. 

          I suggest you use the differential input, so it is easier for customer to layout and avoid the input noise. Or customer use the single ended input, but be careful to make sure there is no differential noise which comes from GND. Shown as below: