ADS1298: ideal frequency AC impedance measurement ADS1298/ADS1299

Hi,

"What is the best ferquency to measure the impedance of EEG electrodes?"

There is no definite answer for this. it depends on electrodes and conditions of surfaces, etc. So customers will need to do tests&data collection&analysis&V&V.

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"What are benefits of having 30/62.5 Hz or more?"

It depends on how much/big of the reactive components are there along the electrodes and signal path and/or peripheral circuits.
E.g.

if there forms some Low Pass filter along the path, then, then high frequency AC excitation may be less suitable as high frequency excitation might be shunt to GND.

if there forms some high Pass filter along the path, then, then low frequency AC excitation may be less suitable as low frequency excitation might be shunt to GND.

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"Why does 1298 has higher minimum lead off detection frequency (62.5Hz) than ADS1299 (31.2Hz)"

One of possible reasons could be that EEG may have signal of interest in higher frequency range; thus, avoid having higher AC excitation frequency; whereas, ECG signal band is usually lower than or in the lower band in contrast with EEG, so may allow higher AC excitation frequency.

Thanks