• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 1014 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8509 / SINAD at DC input, and PSRR vs. supply noise frequency

S.Satoshi
Guru 21675 points
Other Parts Discussed in Thread: ADS8509, ADS8568, ADS8507

Hi all,

Our customer has requested two information for ADS8509 as below. Please confirm it and give your comments.

#1, SINAD at DC input

Our customer hope to know the SINAD at DC input to calculate ENOB at DC input. We know that the SINAD vs. Fin is provided at Fig.15 in datasheet, however it shows SINAD between 1kHz and 100kHz. So we would like to know the SINAD at DC as the reference information.

#2, PSRR vs. supply noise frequency

Our customer hope to know the PSRR performance of ADS8509. We found that PSRR vs. supply noise frequency from the datasheet of ADS8568, so we would like to see such information for ADS8509.

Please feel free to ask me any information via E2E or directly. Your response will be appreciated.

Best Regards,

Sonoki / Japan disty

  • 0
    TI__Expert 5705 points

    Hello Sonoki-san,

    SINAD, SNR, THD and SFDR are not defined for DC inputs. They are all measures of ADC dynamic range that apply only when the ADC input is an AC signal. Since ENOB is computed from SINAD, ENOB also applies to AC inputs only.

    The equivalent of ENOB for DC inputs is called "Effective Resolution", and Effective Resolution depends only on the ADC's intrinsic or transition noise that has a typical value of 1LSB according to the ADS8509 datasheet. Therefore the Effective Resolution for this device would have a typical value of 15 bits.

    Here's a blog post that clarifies the difference between ENOB and Effective Resolution and how to compute them:

    http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/06/13/a-bone-of-contention-enob-or-effective-resolution.aspx

    As for power supply sensitivity, here's a plot from the ADS8507 which has the exact same core and supply architecture as the ADS8509. 

    Best Regards,

    Harsha