Passive High Pass Filter
After the initial amplification step, there may still be some differential DC component that needs to be removed from the signal. This is done with a passive high pass filter configured with a cut-off frequency of 0.5 Hz, which is just outside the EEG band. This filter is enough to filter the DC components event if it is of first order.
This signal processing element is not included in the prototype board but is planned for the production board.
Figure 4: High-Pass Filter Schematic
Figure 5: High-Pass Filter Response