EEG Specific Features
Figure 45. FFT Analysis for Impedance Measurement at 31.25Hz
Out of band Lead off detection
ADS1299 also provides option to do electrode impedance measurement at frequencies outside the EEG
bandwidth of interest. The frequency for this AC current source is set at f
DR
/4. For example to do an AC
lead-off detection at 1 kHz the data rate for the device must be set at 4Ksps. These measurements can be
done concurrently with the EEG measurement.
shows the fft result of AC lead off detection at
fDR/4 with data rate of 4Ksps. The impedance component is present at 1KHz and must be bandpass
filtered. The EEG information is at low frequencies and the data must be low pass filtered to extract the
information. It is recommended to use only nA range current sources for concurrent measurement of EEG
and impedance. For µA range the noise from the current source will be too large and it may swamp the
EEG signal.
39
SLAU443 – May 2012
EEG Front-End Performance Demonstration Kit
Copyright © 2012, Texas Instruments Incorporated
