• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 47 subscribers
  • Views 454 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

ADS1299: How to improve input signal CMRR?

Rock Su
Intellectual 2220 points
Part Number: ADS1299

Dear colleague,

The customer is asking do we have some materials about improving ADS1299 input signal CMRR?

Thanks a lot!

Best Regards,

Rock Su

  • 0
    TI__Guru 55342 points

    Hi Rock,

    Unfortunately we do not. Typically, the CMRR of the ADS1299 is enough for most customers, can you share why higher CMRR is needed? 

    An operational amplifier with higher CMRR can be added before the ADS1299, however keep in mind that the input referred noise from the extra opamp will be multiplied by both gain stages (the new opamp and PGA inside of ADS1299) which may degrade SNR. 

  • 0 in reply to Alexander Smith
    Prodigy 20 points

    Hi Alex smith,

    The CMRR of ADS1299 is enough.The main reason is that the previous bandpass filter（CR-RC ） matching consistency is difficult, resulting in a low CMRR.The consistency is bad because the capacitance precision is difficult to achieve small size and high precision.

    I would like to ask if there is a band-pass filter (bandwidth 0.6~250Hz) to solve my above problem.

  • 0 in reply to changquan lv
    TI__Guru 55342 points

    Hi,

    I would not rely in the signal chain to do the heavy filtering. For the reasons stated, achieving the desired filtering without compromising CMRR is extremely difficult due to component tolerances, leakage currents, etc. It is better to remove frequencies that are not of interest in software. 

    Anti-aliasing filters (RC) are commonly set to higher frequencies to avoid affecting CMRR of the signal chain and the digital filter can be used to limit the bandwidth to ~250Hz if you choose the 1kSPS data rate.