20-bit Delta Sigma problem

[Anonymous]

Is it a good solution, or a bad idea, to use 20-bit delta-sigma ADC (PSoC 5LP) for ECG signals? ECG signal is fast, period is about 1sec, and the frequencies are from 0.05 up to 150Hz. Is the sampling speed of 20 bit ADC (max 187 sps) the biggest problem? Signals from the electrodes are sent to IA (using two PGAs, gain = 2) , then I send signals to ADC, and after that to Filter component (LPF 150Hz). I need big resolution because ECG signal is 0.1-5mV. So I need your help, opinions and suggestions.

[Bob_Marlowe · Accepted solution]

You do not need a large resolution, your signal range is 5mV which would be quite enough for ECG and a resolution of 8 bits (better than 0,5%).

   

What you need is

   

    
• Amplification: Preferably an external instrumentation amplifier.
    
• Noise cancelling: could be done with the filter component (bandpass)
   

   

Most problems will come from the noise from power line at 50 or 60 Hz a sharp notch filter could help.

   

The required conversion frequency should be about 10 times Nyquist which in your case will be about 3kHz

       

Bob

[Anonymous]

Thank you very much, Bob. My another question is - if I want to use only PSoC components, so without external IA, is your suggested solution still possible?

[Bob_Marlowe]

Yes. The PSoC5 has got 4 opamps which you might try to use for your purpose. They are not as precise as you like to have them, offset and bias are not very good, but you can give them a try. Afaik max amplification is ~50 to 100, using a second stage opamp will suffer from offset.

       

Bob