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ADS4149: PSRR in datasheet

Elliot Greenwald96
Prodigy 40 points
Part Number: ADS4149

On page 51 of the ADS4149 datasheet, Figure 104 shows a spectrum with both a tone applied to the input as well as a tone sitting on top of the power supply. 

I'm interested in knowing what the amplitude of the tone on the power supply was to produce the data in Figure 104.

Referring the -81 dBFS tone back to the power supply input through the ~-30ish dB PSRR I get a value of 7.5 mVpp.  However, given PSRR was characterized using a 50 mVpp, I'm wondering if I've erred or misinterpreted Figure 103 or 104 in some way.

Any clarification that could be provided would be greatly appreciated!

  • 0
    TI__Guru* 91947 points

    Elliot,

    Power supply tone signal was 50mVpp which means -32dBFS.

    The tone results in beating components around fundamental as well as direct component.

    Direct component is small (at 81dBFS) whereas the beating components are big (at ~65dBFS).

     

    PSRR is degradation in SINAD which is overall noise floor (including noise, harmonics, and any spurious tone) when power supply tone is applied.

     

    Two significant tones have power summation of ~62dBFS. The power supply tone is at -32dBFS.

    This means PSRR is ~ 30dB.

    Regards,

    Jim