Hi ,

I am working on one application in which I am interfacing AD8232 with Nordic semiconductor's NRF52 to get ECG signal from body. I am applying 1 mVolt signal from ECG simulator to AD8232. Output of Ad8232, I am applying to ADC of nrf52 having gain of 1/6 , 12 bit resolution and reference of 0.825 volt. The output of ADC I am plotting in lab view.

Now at the output of ADC I am getting ECG having peak value of 2000(ADC value) and minimum value as 1100.

As per datasheet of AD8232 overall gain is 1100 V/V. So accordingly, if I am applying 1mVolt as input to AD8232, input to ADC will be 1mVolt * 1100 = 1.1 volt. Now for this input ,ADC output will be calculated as (1.1 volt * 2^(12))/(6 * 0.825)

which is equal to 910.

So, Why I am getting ADC output as 2000 ? Can anyone help me to understand this issue? I am attaching the waveform that I got in Lab view.

Hi,ank

see for calculating ADC resolution the following formula is used

Resolution=Vref/4096 in your case.

so if your Vref is 0.825, then resolution will be 201uV (micro volt)

so for every 201uV change the ADC (digital output) will increment by 1 .

so at last you will get approximately 4096 steps to achieve 0.825 V i.e 4096 at output

so the Vin to the ADC should be in the range of 0 V to 0.825V (0 to 4095) ,if the Vin to the ADC exceed 0.825V your output will get saturated i.e 4095(for any value greater 0.825V in the Vin).so your output should be 4095 not 910.

so here comes the problem .so why the ouput is not 4095 ?

I dont have answer for it ,it may be because of Vref will be different (i.e you dont know exactly the Vref given to ADC )

or the ADC resolution wont be 12 bit it should be different