Why we are using active electrode in electroencephalography (EEG) for collecting brain signal? Nowadays too many biomedical engineers are trying to collecting data signal from the scalp but some don’t know which electrode will be better for them. Today I am explain, what is the basic advantage and why we are using active electrode in electroencephalography (EEG)
- Highest possible input impedance because of minimal signal path length between electrode and first amplifier stage.
- Minimal stray-capacitances of the input.
- Low impedance output of the electrode allows the use of reliable, cost-effective light-weight cables (no need for expensive low-noise heavy coax cables).
- Low impedance output of the electrode combined with matched low input impedance of the AD-box eliminates contact problems in the electrode connectors (no “cracking” when you move the electrode cables or connectors as seen with all passive electrode systems).
- No need for delicate expensive coaxial plugs. Active electrode systems can use convenient multi-pole plugs. As used in the BioSemi setup with 32 electrodes per connector. (Imagine having a spaghetti of 128 electrode cables going to your headbox)
- Low impedance output eliminates artifacts by cable movements. (all systems with shielded coax cable are particularly sensitive to this problem because of microphony and piezoelectric effects generated by the isolation layer between the inner core and the shield).
- No danger for amplifier instability because of the absence of complicated feedback loops with unknown parameters (i.e. electrode impedances and subject stray-capacitances). A cable shield driven by a guarding circuit (see note) forms a loop with positive feedback which may become unstable with particular combinations of electrode impedances and subject stray-capacitances (see this paper for more information).