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ADS1299EEGFE-PDK: ADS1299EEGFE-PDK-SW don't have the Bias sense enable/disable function(REG 3,BIT 1)

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Replies: 3

Views: 84

Part Number: ADS1299EEGFE-PDK

Hi TI's expert,

I downloaded the ADS1299EEGFE-PDK-SW and used the ADS1299EEGFE-PDK boad to test the RLD function, everything works well except that when I wanna enable the Bias sense function ,I can't find a choice on the software to configure it. I tried to  change all the choices on the software but the reg3 bit 1 just keep read as 0, Also the Debug-Manual register write seems didn't work(do not know how to use it,click on the right button with 03,seems no response,or else I can mannually write 1to that bit ) See below pics.so I can't enable the RLD function ,the ECG wave shows a large 50HZ common mode noise.

BTW, In our own ADS1299 board we can write the register 03 bit 1 to 1 and it seems working well.

What can I do to enable that ?or do you have a new version of the sofware?

Thanks very much

Tinky

  • Hello Tinky,

    Thank you for your post.

    The BIAS lead-off sense function is not available on the EVM. By default, this bit is set to 0. This function is only meant to check the connection status of the BIAS electrode. In the actual application, you will have to temporarily power-down the BIAS amplifier to check the status, then enable the amplifier again to resume normal measurements.

    The BIAS lead-off sense function is independent of the main function of the BIAS electrode, which is to establish the common-mode voltage on the body and cancel the common-mode noise measured by the input electrodes. You can continue to use the BIAS electrode to reduce common-mode noise without this lead-off function. Please refer to our E2E BIOFAQ page for some useful collateral on using the BIAS electrode (also referred to as RLD electrode) to improve CMRR.

    Regards,


    Ryan Andrews

    Applications Engineer | Precision ADCs 

    Are you working on a bio-potential application? Check out these helpful resources: ADS129x BIOFAQ | ECG Online Training

  • In reply to Ryan Andrews:

    Hello Ryan,

    Thanks for your prompt reply. 

    1.From sba188 we know that  the  fBW caculation:

    and in the ADS1299_EVM the RF CF are(RF=392k,CF=10NF),then fBW=1/(2*3.14*392k*10n)=40.6Hz,is it a Low Pass Fitler?Then how can it cancel the 50Hz CM noise?

    In the datasheet the value are 1Meg and 1.5nF then the fBW will be more than 100Hz,I think that is more rational. what value do you think we should use in China(220v/50Hz)?

    2. The datasheet recommand we using the differential cap between P and n in the inputs,but the EVM uses the shunt cap to GND,I used both methords in our own board(5V singal supply differ from its bipolar+2.5/-2.5 Power suplly ) and found that the shunt methord's CM noise it less than the differential one.what should I choose?

    In the datasheet:

    in the EVM:

    regards,

  • In reply to tinky1999:

    Hello Tinky,

    1. The EVM components should be adjusted to increase the RLD closed-loop bandwidth beyond 50 Hz / 60 Hz. The suggested circuit in the data sheet makes more sense with a bandwidth of 106 Hz.
    2. The common-mode caps helps to reduce the common-mode noise on the electrodes. If the signal of interest is the differential measurement between two input electrodes, a differential filter will help to reduce out-of-band noise. The differential filter should be set about a decade beyond your signal bandwidth of interest, and the common-mode filters should be about 10x higher in frequency to maintain good CMR.

    Regards,


    Ryan Andrews

    Applications Engineer | Precision ADCs 

    Are you working on a bio-potential application? Check out these helpful resources: ADS129x BIOFAQ | ECG Online Training