A Controllable Gain Amplifier Circuit for EEG Acquisition System

A controllable gain amplifier for analog front-end is proposed, which can effectively improve the dynamic range of the received electroencephalography (EEG) signal and reduce the signal attenuation. The amplifier consists of two-stage amplifier with fully differential structure; the first-stage amplifier uses a high input impedance operational transconductance amplifier (OTA) with integrated low-pass filter to suppress DC offset; the second-stage amplifier uses a current-voltage controllable gain transimpedance amplifier (TIA) with switching array control resistors to achieve controllable gain. Simulation results show that the open-loop gain of the first-stage op-amp is 45 dB and the open-loop gain of the second-stage op-amp is 90 dB at a supply voltage of 1.8 V. The gain can be adjusted from 5 dB to 45 dB after adjusting the bias voltage.