Hi everyone, it's my first post here !
I am trying to develop some 3 poles (+ , - , ref) electrodes with pre-amp stage for EMG signals acquisition. I was hesitating between AD8421 and LT1167 because both have very good performance for this application but I will choose LT1167 because of a higher input impedance (100 Gohm vs 30 Gohm for the AD) as I use gold plated electrodes.
I was digging into the datasheet and found an example schematic entitled "nerve impulse amplifier" about indeed EMG acquisition :
My question :
I don't really understand this configuration with the patient ground (is it like a reference electrode ?), why is the Ref pin 5 connected to GND and not to the patient ground and thus why do they fix this electrode potential to the GND potential ? In the datasheet is said that the LT1112 OP Amp pin 1 creates a ground for the common-mode signal, I don't understand that. My (probably incorrect) thoughts are that the ref pin 5 should be connected to the body potential outside of the muscle activation zone to provide the common-mode signal ?
As I want to use a reference electrode in my system sould I connect it directly to the pin 5 and forget about this patient ground part and not to the 0v GND ?
Thanks in advance !
I am trying to develop some 3 poles (+ , - , ref) electrodes with pre-amp stage for EMG signals acquisition. I was hesitating between AD8421 and LT1167 because both have very good performance for this application but I will choose LT1167 because of a higher input impedance (100 Gohm vs 30 Gohm for the AD) as I use gold plated electrodes.
I was digging into the datasheet and found an example schematic entitled "nerve impulse amplifier" about indeed EMG acquisition :
My question :
I don't really understand this configuration with the patient ground (is it like a reference electrode ?), why is the Ref pin 5 connected to GND and not to the patient ground and thus why do they fix this electrode potential to the GND potential ? In the datasheet is said that the LT1112 OP Amp pin 1 creates a ground for the common-mode signal, I don't understand that. My (probably incorrect) thoughts are that the ref pin 5 should be connected to the body potential outside of the muscle activation zone to provide the common-mode signal ?
As I want to use a reference electrode in my system sould I connect it directly to the pin 5 and forget about this patient ground part and not to the 0v GND ?
Thanks in advance !