A Chopper Modulated Amplifier System Design for in vitro Neural Recording

Abstract

Neural recording systems measure very low-amplitude signals of less than 5 kHz bandwidth. Low-frequency noise processes such as flicker noise and DC offset can degrade the quality of recordings made by such systems. A chopper modulated amplifier system is described and shown to reduce the flicker noise in neural recording systems by 10 to 20 dB. The amplifier system was implemented using the MOSIS ABN 1.5 micron technology. While the amplifier system contained an imperfection that prevented it from working with actual tissue samples, it worked well enough to prove that chopper modulation does reduce flicker noise appreciably. All of the details are presented along with studies of gate-metal-free transistors and custom-made MOSIS-based recording electrodes.