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Active electrode design for surface EMG.

Question asked by RkTim on Mar 17, 2015

Hello out there,

 

I am a EEE undergrad student and looking for some help with my project. I am designing active electrodes to acquire surface EMG signals. Active electrodes, if you don't know, are electrodes that are directly connected to a pre-amp and filtering stage in one compact unit before transmitting the signal. Apart from designing the active electrodes, I have been tasked with finding a method for eliminating the REFERENCE electrode common in most EMG/ECG/EEG instrumentation. I have been able to research and find two methods that could eliminate the reference electrode;

1. Using a system of a voltage divider and a voltage follower to drive the reference pin of the IN-AMP's to mid supply and

2. Using an op-amp integrator connected to the reference pin and feedback from the IN-AMP output via a resistor to remove the DC offset.

I have been using the double differential mode to acquire the signals from the electrodes using 3 AD8221A  instrumentation amps. I have run some simulations but I believe I am not testing it right.

 

My question is in 3 parts;

1. Do any of the methods I have mentioned above make sense and are they reliable?

2. The reference electrode in most designs Is the unequivocal ground and everything else in the system that needs to go to ground is connected to that point, if I eliminate the reference electrode, how do I then ensure a ground plane on my PCB design?

3. If the two methods above are not suitable for the IN-AMPs could someone perhaps suggest a method that could work?

 

I have attached a schematic of my design simulation on Multisim 13. The schematic does not include the design for the filters as I will be using Sellen Key structured High pass and low pass. it also does not include the design of the intergrator connected to the reference pin as I do not know how pick suitable values for the Capacitor and resistor.

 

Any help will be much appreciated!

Tim.

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