A 16 GΩ Input Impedance Amplifier with Flicker Noise Reduction for Neural Recording Applications

An analog front end (AFE) stage used in neural recording requires a buffer amplifier with high input impedance in order to not attenuate the signal and to avoid polarization of the recording electrodes. In such applications, due to the low signal frequency, the SNR is limited by the flicker noise, and hence chopped amplifiers are often used. However, chopping reduces the input impedance of the amplifier from the giga-ohm range (that of input MOS transistors) to the mega-ohm range. In this paper, we present a transconductance amplifier which uses a novel chopping scheme that does not reduce the input impedance, while significantly suppresses the flicker noise. The prototype amplifier was fabricated in 65 nm CMOS process and has an input impedance of 16 GΩ even when chopping is enabled.