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SNR calculation for audio amplifer

Mahendra Patel1
Expert 3560 points
Other Parts Discussed in Thread: LM4675

Hello Team,

One of my customer is using following device in their design,

  1. TPA2005
  2. LM4675

There is SNR specification of 97dB mentioned in the datasheet at Vdd=5V, Po=1Wrms, Av=2, temperature=25 deg C.

Can you please let me know how much would be SNR at Vdd=5V, Po=0.5W, Av=2.83, temperature = 44degC?

Is there any calculation method or graph for SNR vs temperature /gain / Po? 

Regards,

Mahendra, TI.

  • 0
    TI__Guru** 110615 points
    Hi Mahendra,

    To calculate SNR you need to know your signal characteristics (it could be power or amplitude) and the noise in that signal (often named as output noise or noise voltage).
    The formula to calculate SNR is : SNR=10log(Vrms_signal/Vrms_noise)^2
    You can approximate Vrms_signal with the following: Po=V^2/R_load

    I hope this solve your questions.
    Let me know if you need further support.

    Best regards,
    Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 20 points
    Hi Ivan,

    I know the noise in the signal, but I want to know how much noise would be contributed by PA only.
    The LM4675 PA datasheet mentions output noise 28uV at Vdd = 3.6V and Ci=2uF, gain=2, T=25 deg C.
    How to get PA noise at Vdd=5V, Ci=22n, Gain=2.83V, T=44 deg C.

    Regards,
    Vidya