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-Presented herein is a fully integrated low-noise CMOS multi-channel amplifier for neural recording applications. The circuit employs the chopper modulation technique to reduce the effect of flicker noise and DC offset. A reduced area design implementation is achieved by trading off the increased noise margin performance of the chopper modulator for minimal amplifier area and analog multiplexing of the recording sites. A fully differential topology is used for the signal path to improve noise immunity. The analog amplifier exhibits 56 dB of gain with a 115 kHz bandwidth and a common mode rejection ratio (CMRR) of 80 dB. Simulation results show a total input referred noise less than 16 nV/√Hz. The system power consumption is approximately 750 µ µ µ µWatts. The fully integrated system was designed in ABN 1.6-um single poly n-well CMOS process. Keywords -Neural recording, chopper technique, switching noise, flicker noise I. INTRODUCTIONThe steady advance in CMOS IC processing technologies has stimulated the rapid growth of electrode array micro-sensors used for neural recording applications. The use of a single silicon substrate for both CMOS integrated circuits and neuron cultures provides an attractive approach to experimentally monitor and stimulate the electrical activity of neural arrays. The ability to record neural signals using CMOS circuitry has previously been demonstrated [1]. Some of the work involves "in vivo" recording of the neural signals [1], in which the recording sites are inserted to the live animals whereas others study "in vitro" recording of the neural signals, in which the neurons are cultured outside of the body [2].In [1], a neural recording probe with multiple recording sites and CMOS signal processing circuitry was fabricated on a shared silicon substrate. The front-end system consisted of 32 recording sites with 8 channels allocated for analog signal pre-amplification followed by an 8-to-1 analog multiplexer. The pre-amplifiers were designed with large area PMOS input devices to partially address the 1/f noise while high pass filtering was used to minimize signal DC drift. In [2], an "invitro" characterization of 2-D network of neurons was implemented. However, the analog amplifiers were not integrated with the recording sites. Harb et. al. [3] describes an implantable instrumentation amplifier for low-amplitude signal amplification using the chopper stabilization technique. However, the signal amplification is implemented with two amplifier stages that include a selective filter, resulting in increased silicon area. Furthermore, the system is applicable only for single channel recording.In this paper we present a fully integrated amplifier circuit used in neural recording systems. The system is designed to stimulate and monitor the electrical activity of a large population of neurons using an array of recording sites within a shared substrate. The recording sites are implemented with "open-gate, metal -free" insulated-gate field-effect transistors for direct coupling of the ne...

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