Dear sir or madam,
I configured my ADAS1000 according to Example 4 in datasheet (activated bit to send header only when data is busy).I have no skipped frames nor any faults exist in HEADER register.
As a first question, I would like to kindly ask you if you could help me resolve the fact why do I have such a deformed amplitude (enclosed snapshot) of 150Hz sinusoidal frequency (it applies to all 3 lead words). The problem is not in the process of deriving the voltage value as the raw ECGData value is also fluctuating in the same fashion.
Moreover, would you be so kind and explain me why the offset is shifted to 1.3V in TESTTONE measurement? From datasheet, I see that min value of GAIN0 is 0V and maximum is 2.3V, but typical is 1.3V. Does that mean that the signal I am measuring must be shifted to offset somewhere between 0-2.3V or this is done automatically? I know that in Example 4, we have the SINGLE ENDED INPUT set up, therefore (if I understand it correctly) we have 150Hz sinusoidal frequency with 1mV amplitude connected to + sign of the differential amplifier and 1.3V to - sign branch of the differential amplifier therefore I would expect that these two signals are subtracted and it should be fluctuating around -1.3V not 1.3V
I somehow guessed that in this ELECTRODE mode, values could be only positive but I do not understand how we managed to get 1.3V with differential amplifier with 1.3V on - and 1mV on +, I can get only values between:
Minimum value (000...) = 0 V
Maximum value (1111....) = 2 × VREF/GAIN
LSB = (2 × VREF/GAIN)/(2 N – 1)
ECG (voltage) = ECG Data × (2 × VREF/GAIN)/(2 N – 1)
Therefore it must be possitive, but how and why?
But I do not understand how the differential amplifier works this way, should I undestand it as not a differential amplifier but a summation of VCM signal (like WCT) creating a sort of a virtual lead and the sinusoidal signal is superimposed to VCM signal, expecting maximum voltage of 1.301V? This also relates to my second question.
My second question is the fact that I do not understand why my signal is fluctuating around 1.26V randing from 1.262V to 1.264V which is moreover exceeding the expected amplitude peak-to-peak 1mV, in ideal case I would expect it to be varying between 1.301V to 1.300V or 1.300V to 1,299V. I have enclosed snapshot.
Thank you very much and wish you all the best to new year!
[edited by: Ivo Hora at 11:45 AM (GMT -5) on 31 Dec 2020]