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ADS1191

Darren Jenkins
Genius 13471 points

Other Parts Discussed in Thread: ADS1191

Hello Precision data converter experts,

I have a customer asking the following questions.  Could you help out? 

1)      Can TI provide some information or an application note on ECG sensor positioning on the body and the ADS1191 parameter settings? Right now we are looking to optimize the gain and sampling frequency of the chip based on a two electrode ECG placement; one on the left wrist (LA), one on the right hand (RA).

2)      The right leg drive circuitry (RLD) is used to improve the common-mode noise rejection between the two electrodes. We have discovered that by connecting a high impedance between the RLD output and the ECG inputs, the CMR is improved. Can TI provide us with some more information regarding the RLD and grounding of the system to improve the signal to noise ratio and resistance to motion artifacts. The system is to be battery operated and mounted on the user’s wrist.

Thanks,

Darren

 

  • 0
    TI__Guru 69086 points

    Hi Darren, 

    1.) When choosing the amount of Gain to use, the customer has to keep in mind the full-scale differential input range is equal to +/- VREF / Gain. The ideal setting is the one that maximizes your input signal relative to your reference voltage to increase your effective resolution. Using a larger gain also reduces the input-referred noise from the device.

    In choosing your sampling rate, remember that the bandwidth of the ADC is Data Rate / 2, due to Nyquist. So, it depends on your frequency range of interest. Typically, customers look at ECG signal content between frequencies of 0.05Hz and 150Hz, so I would suggest sampling at least at the default 500SPS.

    2.) There's a nice app note on using the RLD to improve CMRR: http://www.ti.com/litv/pdf/sbaa188. The customer might like to read through this for a better explanation on the theory behind this technique.

    Kind Regards,