Notch Filter

The next filter filters the high amplitude common mode powerline signal which may still pass the instrumentation amplifier with unity gain. This noise is tightly located at 60 Hz and so we use a notch filter to remove it. The filter is an active twin T design with a center frequency of 60Hz which can be slightly tweaked with a potentiometer. This is shown in figure 7 with multiple traces showing different potentiometer values inside its range. The quality factor is planned to be configured at a value of 2 for the production board since tests with the prototype board showed that when the quality factor is to high, the filter is not effective.

Figure 6: Notch Filter Schematic

Figure 7: Notch Filter Response