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How to measure ADC Noise free bits

Hithesh
Genius 3290 points

How would one go about measuring ADC noise free bits. 

Let's say a 16-bit ADC has 14 noise free bits. How do I measure the performance once the ADC is on the PCB.

If the FS range is 10V, each LSB will be 150uV.

Apply a known voltage, say 1.000v and record the digital code. If the ADC has 14 noise free bits, then the variation in the digital code should correspond to 1.000V +/-0.6mV?

  • 0
    TI__Guru* 92655 points

    Hithesh,


    Basically that follows. The equation to calculate this is explained below:

    Noise Free Bits = ln(FS range/p-p noise)/ln(2)

    In your example, the full scale range becomes 10V, and the peak-peak noise is 600uV. Calculating this out

    Noise Free Bits = ln(10/0.0006)/ln(2) = 9.72/0.693 = 14.0 bits.

    Sometimes there are other considerations. If the input is bipolar, then often the full scale range is the 2x the reference. Also, the noise free measurement is done when the input =0V, to remove the effect of reference noise. Regardless, you can use the equation to determine noise free performance.


    Joseph Wu