Unlike other DSI multi-channel biopotential transmitter models, the F20-EET and F40-EET standard modules do not include a separate, externalized reference electrode. The reference electrode is connected internally to the negative lad of Channel 1. Testing confirmed that this configuration does not have a measurable effect on the data collected for EEG and EMG applications. This is largely due to the similar amplitude and frequency ranges in these signal types. It is recommended that the lower amplitude signal be measured using the Channel 1 electrodes. Channel 2 of the implant is shared between the temperature and biopotential electrodes.
The temperature and biopotential signals are combined in the implant data stream. The acquisition interface then filters the signal. First a filter will accept low amplitude, which reproduces the temperature data. Next, a filter accepts high amplitude changes, which reproduces the biopotential signal.
EOG Signals are of sufficiently low amplitude that the signal may pass through the filter that is meant to separate the temperature data. Because of this, there may be low amplitude and frequency variation introduced into the temperature data that corresponds to the EOG signal.
This consideration is not necessary for other implants that have a separate reference/common electrode and do not have any shared channels, like the D70-EEE.