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PGA202 noise performance

Dave Cooper
Prodigy 210 points
Other Parts Discussed in Thread: PGA202

A PGA202 at 60db has 37mVrms of output noise with less than 1uVrms at the input. This is with 47pF added to the compensation pins for 100KHz bandwidth.

The same measurement is 50mVrms with no capacitors added [1MHz bandwith].

Still with 100KHz bandwidth, changing the gain to 40dB, 20dB, and 0dB results in noise voltages of 3.7mVrms, 260uVrms, and 10uVrms respectively.

Given the input noise voltages and noise voltage densities in the data sheet, are these measurements the levels I should expect, or is there something I should resolve?

Thank you for you help, Dave.

  • 0
    TI__Guru 62705 points

    Hello Dave,

    The output noise levels you're measuring seems higher than expected if you're measuring the RMS output noise as shown in the calculations below.  Is it possible that you're measuring the peak-to-peak output noise instead of the RMS output noise?  If so, your measurements are in line with the calculations below.

    The input noise density is constant at 12nV/rt(Hz) from the datasheet. 
    The output noise RTI is equal to 400nV/rt(Hz) / Gain. 
    The total noise density RTI = SQRT(input_noise^2 + output_noise_RTI^2). 
    The total RMS noise RTI is equal to the total noise density RTI multiplied by the SQRT(bandwidth *1.57). 
    The total output noise RMS is the RTI noise RMS multiplied by the gain.
    The total output noise peak-to-peak is the RMS output noise multiplied by 6.6.

    If you're measuring the RMS output noise can you share your schematic with all source (input) impedances noted so we can run calculations based on your circuit configurations.  Have you verified that the power-supplies you're using are not introducing extra noise?

     

  • 0 in reply to Collin Wells
    Prodigy 210 points

    Hello Collin,

    Thank you for your helpful response.

    I am taking more measurements for my reply.

    Best regards,

    Dave