Choice of ad8232 or ADAS1000-3 chip to take ECG signals

I am currently developing a device that analyzes the ECG signals to basically study the bit rate. I am using the AD8232, but I have been evaluating the possibility of changing to the ADAS1000-3, but looking in its datasheet I found a part that indicates that it has an internal ADC of 14 bits, but in the technical specification of the gain configuration it appears 19 bit of resolution.
My problem is this, I am using an AD8232 that is connected to a 16-bit ADC and I have a total gain of 1800. If I use the ADAS1000-3 my resolution in the ADC and the gain will be lower?
Thank you for your answer.
This is my concern for the moment.

  • 0
    •  Analog Employees 
    on Mar 29, 2018 12:44 PM

    Hello Ever,

    Thanks for message.

    The ADAS1000 uses a 14-bit 2MSPS ADC, then uses various stages of decimation follow to reduce the sample rate and increase the number of effective bits. The drawing shown in Figure 75 of d/s shows an overview of the decimation/filtering stages.

    The outcome is a 24-bits wide (19-bit usable) 2kSPS result, this gives you 19bit performance at this data rate.

    The ADAS1000 was designed for use a DC coupled system - where the small signal of interest (ECG 1mV level) is digitized along with the larger electrode offset (could be +/-300mV to +/-1V). In this type of system, the gain needs to be limited. The ADAS1000 has programmable gain of 1.4 up to 4.2, this is configured through a register setting.

    DC coupled systems like this typically require higher resolution convertors as a result.

    The AD8232 approach is slightly different in that I think it's ac-coupled, removing the electrode offset and thereby allowing you use higher gains to amplify the signal of interest. https://ez.analog.com/docs/DOC-13886

    hope this helps..

    best regards,

    Catherine.

  • 0
    •  Analog Employees 
    on Mar 29, 2018 2:45 PM

    Hello Ever,

    Ok, this is a very small signal to measure with the ADAS1000, it's really beyond the parts capabilities.

    The signal you are trying to measure will likely be swamped by noise (depending on what gain you can tolerate), the noise performance of the ADAS1000 is a listed in the datasheet, on the order of 5uV pp to 30uV pp typically.

    In this case, you may be better positioned to continue with the AD8232 for your application.

    Let me know if you have other questions.

    best regards,

    Catherine.

  • Thank you very much for your answer. Now I understand better.

    What happens is that I am taking the ECG signal in the abdominal region, therefore I am not working with a traditional ECG, and I need to capture signals in the order of 20uV or 60uV. Using the ADAS1000 would have problems to capture signals in this order of the uV?

  • Thank you very much. 

    With this I am clear, and I understand that the best option is the AD8232. I thought that the ADAS1000 could be a better option for having lower noise levels, but the gain factor is decisive for capturing the signals.