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ADS127L11: Typical Characteristics

Junjia Su
Prodigy 111 points
Part Number: ADS127L11

Tool/software:

I want to know how the 6.11 figure in datasheet was tested.

What’s the meaning of "Short input FFT"

What is the output（y axis） in the graph ?

 From which terminal（pin） this amount is measured ？

What does this data represent about ADC performance? It doesn't seem like data like ENOB is intuitive and generic ？

I would like to have an answer from the relevant engineer . THANKS!

  • +1
    TI__Mastermind 46860 points

    Hello Junjia,

    This data was taken with the ADC inputs shorted together, and connected to a mid-supply (2.5V) common mode voltage.  Pins 1 and 2 of the RUK package shorted and connected to 2.5V with respect to AVSS.  AVDD1=AVDD2=5V, AVSS=GND and Vref=4.096V.

    The y-axis is dB relative to full scale input, or dBFS.  With Vref=4.096V, the maximum rms voltage of a sinewave will be 4.096/sqrt(2)=2.896Vrms.  Each of the frequency bin peaks are -170dB or lower.  The maximum rms voltage of each frequency bin will be 2.896V*10^(-170/20)=9.159nVrms.

    The primary purpose of providing this data is to show that there are no significant noise spurs (or tones) in the spectrum; the noise is primarily flat and due to thermal noise.  

    ENOB requires a sinusoidal input signal near full scale; you could estimate dynamic range or effective resolution, but you would need the detailed data for the plot.  For these measurements, it is better to use a histogram and directly calculate the total noise.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    TI__Prodigy 111 points

    Thank you for your answer.

    from your answer："The maximum rms voltage of each frequency bin will be 2.896V*10^(-170/20)=9.159nVrms." 

    Are these equivalent input noises also measured at the input? Or is the relevant conversion done via the output digital code values?