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PGA4311: Gain Control for differential signal performance

Lenny
Intellectual 700 points
Part Number: PGA4311
Other Parts Discussed in Thread: PCM1794A,

I am wondering if the dynamic range of the device can be improved by using channels 1 & 2 for a differential signal and also using channels 3 & 4 for a second differential signal.

Currently I am using a dual PCM1794A (in monaural mode) and am getting 128dB SNR and a THD+N of 0.0004%, but I do not have volume control.

I tried to find a volume control for the I2S side but am coming up with nothing.

If I use the PGA4311 how will my SNR and THD+N be affected?

  • 0
    TI__Expert 5830 points
    Hello Lenny,

    Thank you for posting your question on the E2E Forum. An applications engineer from the precision amplifier team will be able to address your post during standard business hours.

    Best regards,
    Errol Leon
    Texas Instruments
  • 0
    TI__Expert 6250 points
    Hi Lenny,
    You may see 1-3dB of degradation to SNR due to noise from the PGA4311. I'm basing this off of a calculated noise level of ~5µVpp from the 128dB SNR of the PCM1794A with a 4.5Vrms output, plus the 2.5µVpp to 4µVpp output noise of the PGA4311. Since these two noise sources are uncorrelated, they are added as root-of-sum-squares.This assumes a gain of 1x for the PGA, and I'd expect worse SNR as the PGA attenuates more and more, due to the smaller signal level present at the output.

    With an A-grade PGA4311, a reasonable estimate for THD+N would be ~.0006%. This again comes from a root-of-sum-squares addition of the two THD+N figures.
  • 0 in reply to Alexander Davis
    Intellectual 700 points

    Hi,

    Are you describing a case with single ended input and single ended output?

    I plan on using this with differential output from the PCM1794A (monaural mode), in this case the (+) side would be gain controlled from one input and the (-) side would be gain controlled from a second input on the PGA4311, in this scenario the gain on the two inputs would always be set to the same value. Also the gain would never be set to be more than 0dB, I would only use the PGA4311 as an attenuator.

    In this case is the output noise from the PGA4311 correlated (since it will be common mode noise), how much affect will this have on the differential signal?

    Thanks;

    Leo

  • 0 in reply to Lenny
    TI__Expert 6250 points
    Hi Leo,

    The noise should still be uncorrelated between two channels of the PGA. For a differential output, this will add another 1-3dB degradation to the SNR. Using the same calculations from my post above, THD+N would increase to around .0008%