EEG Recording System

Posted on Feb 5, 2014

Continuous monitoring of brain activity is essential in understanding neural substrates of many physiological and pathological brain functioning. Low amplitude of EEG signals as well as their noisy nature make it hard to detect them (1-500 uV and. 1-500Hz). Another issue is the DC offset of the signal due to electrode-tissue interface. This DC off

EEG Recording System
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set is usually 20-50 mV and 1000 times bigger than the signal. Thus, a very low a noise instrumentation amplifier is required to amplify these signals and remove the DC offset. Typically, electrodes are placed on the scalp of patients and a large number of wires connect to a huge rack of instrumentation amplifiers connected to a computer. This makes the patient very uncomfortable. Also, the advent of fully implantable microelectrode arrays has created the need for integrated micropower amplifiers. Several chips for EEG or neural recording have been reported in the literature [1]-[5]. [1] introduces a circuit that has a 7. 8 uVrms input referred noise, which is above the signal amplitude. Noise issues are solved in [2] at the expense of relatively large silicon area, 2. 2 mm by 2. 2 mm. [3] and [4] don`t mention noise figures, and [5] uses a BiCMOS process to obtain a low noise amplifier. Off-chip capacitors are used in some of the designs [6] to reduce noise but they are less suitable for implantable microsystems. Here, we design an EEG recording system that amplifies the signal and produces a digital output that can be connected to a RF chip, so that data can be sent wirelessly to a base station. The system has four channels so that four EEG data streams can be recorded simultaneously. The amplifier has a gain of 100 db and input referred noise of 4. 4 uVrms, while consuming 72 uW of power form a 3. 3 V power supply. It...

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