Low-noise amplifier with sample & hold for high-density stimulation and recording of neural signals

In this paper, the design of a low-noise amplifier (LNA) for a 32x32 pixel microelectrode array (MEA) is presented. Its gain and noise amount to 50 dB and 10 μVrms, respectively, at a bandwidth of 66 kHz. The LNA consumes less than 85 μW. The integrated offset compensation circuit makes the system less sensitive to mismatch and variations in the culture medium biasing voltage. A sample&hold (S&H) buffer stores the amplified input signals locally, thereby realising an electronic shutter function. This allows for simultaneous acquisition of all pixels. The on-chip logic permits individual selection of every single pixel at any time. As a result, regions of interest (ROIs) of any size can be defined. Accordingly, the entire cell culture or subregions can be observed at a high sampling rate. Moreover, each pixel is equipped with a stimulation circuitry. Centered around a programmable SRAM cell, it offers the creation of complex stimulation patterns on the MEA. The entire circuit has been layouted in 180 nm, 3.3V CMOS technology and covers an area of 60x60 μm2.