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Q: The ADAS1000 device was designed as an ECG front end. Can I use it for EEG applications?
A: Firstly let's look at the differences between an ECG and an EEG signal:
An ECG (electrocardiogram) is 'sensed' on the surface of the patient, on the skin typically using Ag/AgCl electrodes. These electrodes form an interface between the ionic flow of the heart and the surface electrode which basically receives the synchronized depolarization/repolarization of the heart on a beat by beat basis (Cardiac cycle). The ECG "electrodes" are placed in various positions on the patients chest,arms,legs capture these signals from the heart. The magnitude of these ECG signals is in the region of 100uV to 5mV. The ECG analog front end needs to be able to digitize these signals while rejecting the common mode signal that is also present due to AC mains and other environmental signals. As a result the CMRR of the system must be in excess of 105dB (where RLD or driven right leg is used).
For ECG applications, the various medical standards dictate the maximum input noise floor at 30uV pk-pk, which applies specifically to the instrument (system level).
For EEG signals the electrode offsets can be almost as high and the input signal levels are on average at least 20 times lower meaning the noise floor must be on the order of 1-2 uV over a typical bandwidth of interest (0.1 to 80 Hz).
The ADAS1000 was designed for ECG applications, targeting noise performance that would support the required noise floor according to the various medical standards applied to the system level. The noise performance of the ADAS1000 is greater than that required by EEG applications, therefore the device is not suitable to be used directly as is in EEG applications.
However, with the application of external gain and removal of the DC offset component prior to the ADAS1000, it may be possible to use in some EEG applications.