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Inquiries regarding ADCPro usage for ADS1282EVM

Atsushi Okui
Genius 4015 points
Other Parts Discussed in Thread: ADCPRO, ADS1282

Hall-san,

Thank you for your previous support towards the inquiries regarding ADCPro usage for ADS1282EVM from our customer.

With regard to the inquiries on the thread below, we have additional inquiries from them.

e2e.ti.com/.../1447055

Please refer to the items below, and feedback us with your comment.

1) When we did FTT analyze with shorting A+ and A- on J6A of ADS1282EVM each other, we found peak noises at 20Hz and 40Hz. 


Please let us clarify whether these peak noises are also Idle Tones.

2) When setting Preamp inputs shorted through 400ohm, the above peak noises were moved. 


Please let us clarify whether this was caused by the offset differences on this device and input amp on board or not. 

3) When referring "Figure 35. PGA Noise" on page 15 of ADS1282 datasheet, we found that the frequency characteristic would be changed based on the status of PGA Chop. 

However, we could not find out this characteristic change on ADS1282EVM even though we change the status of Chop checkbox.


Please let us clarify how we could observe this on ADCPro.

4) Even though we did uncheck the Chop checkbox on ADCPro, we still observed 8kHz peak noise if observing with setting SINC filter into 8kHz.  

Please let us clarify how we could resolve this issue.

We thank you once again for your information.

Best regards, 

  • 0
    TI__Guru* 92655 points
    Atsushi-san,


    As you have mentioned is likely that the peak noise that you are seeing are idle tones.

    If you have not seen this, idle tones are discussed in the datasheet. There is a description of idle tones on page 12. By shorting the inputs through 400Ohms, you may be changing the offset of the measurement with the input bias current reacting with the resistance to shift the idle tones to different frequencies.

    For the chop status, there are two things to check. First, it's possible that the sample size is too small to see effect of the 1/f noise. I would use a larger block size to get about 10 seconds worth of data. Second, when the device is in a PGA gain = 1, you are dominated by the ADC noise which would have low 1/f content. Try setting the PGA gain to a higher setting and repeat experiment with Chop on and off, and you should see a difference.

    The 8kHz chopping is from the chopping of the modulator itself and is described in on page 15. The chopping that can be enabled and disabled with the switch in ADCPro is for the PGA, which also uses a chop frequency of 8kHz.


    Joseph Wu