An Ultra Low Power Low Noise Chopper Amplifier for Wireless BEG

The realisation of wireless EEG systems suitable for long term monitoring requires low noise, low power and low voltage circuit design. Presented in this paper is a 1 V, 1.4 muW chopper amplifier implemented in a 0.35 mum CMOS process. The achieved input referred noise voltage is 1.5 muV rms and the gain is 44 dB. Since the dynamic range of the input EEG signal is dominated by the offset voltage generated at the electrode-tissue interface, a novel input high pass filter has been designed. The required filter capacitance is limited to 40 pF by recognising that the input chopper switches can be combined with the amplifier input capacitance to emulate a large resistance.