ADS1292: One lead ecg better CMRR OPA2188 and ADS1292 .

Add info 

Or add INA828  and use ADS1292 as single end

Does these solution have some effect to increase the performance ;  and do i still really need to  to deedback RLD with high resistors to the inputs ? 

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Hi Hector,

Thank you for your post.

The CMRR performance is dependent on all components in the signal chain. The ADS1292 already offers high enough CMRR to satisfy IEC standards. I don't believe another amplifier or INA in the signal path is necessary.

To improve CMRR performance, I would begin by reducing the component tolerance for the resistors and capacitors used in the signal path. Much of the CMRR degradation comes from the mismatch in discrete components. This causes common-mode to differential signal conversion, so the high-CMRR amplifiers at the end of the signal chain will not help. 

With only 2 electrodes and no RLD, another method must be used to bias the input signals to mid-supply. An AC-coupling capacitor and a high-impedance pull-up to RLDOUT is one way to achieve this.

Best regards,

Thank you for reply . 

i will test what u say ; the problem in our application we use pads with jel not electrods ; that effect the all performance

 does it matter where to put the capacitor at the inputs of electrodes or at the inputs of th ADS1292 ? 

i usually start with low pass allaising filter then AC capacitors  then pull up resistors  . Am I right? 

Mr Rayn I would like to thank you very much for you great support 

its really help 

i share my shamatic ; do really I need the diff capacitor ? C178 

how can I mute the input block capacitor and the pullup resistors ? 

I undderstand from the datasheet if I need 8khz sps I have to use external oscillator , right? 

Thank you again 

Abig thank  for you for simulation the filter

U use bipolar supply +/- 2,5 volt  , so all should be the same , right? 

i wil leleminate the 100k ; 

i mean by mute to decrease a little the input capacitance (1uf )if possible . 

Also I need to increase the filter frequency  about 1500hz because i need to detect the Pace signal in the software . so i should play with the resistors little . 

thank you again 

What about add a ressistor in serios with the capacitor for limit current and protection  between electrodes and capacitor  ?  how does this resistor effect the above circuit? 

Thank you 

Do I need buffer between protection resistors and  Dc block capacitor ? 

Any help here please ? 

Hi Hector,

Yes - bipolar and unipolar supplies will give you the same performance.

I suppose you could use a high-impedance protection resistor before the DC-blocking caps, as the caps would remove the DC offset they introduce. A 1k, 1W resistor is typically all that's needed up front. As an example, please refer to this TI reference design:

http://www.ti.com/tool/TIDA-01614

For more information about electrical overstress protection, check out our new TI Precision Labs - ADCs training videos:

https://training.ti.com/eos-and-esd-adc

Best regards,

Thank you for your grear answers ; its reallt help

my last question ; we will go with 5v  unipolar solution 

for the low pass filter at the input should I connect the capacitors to ground or 2,5v 

thank you