Exploiting the 1/f structure of neural signals for the design of integrated neural amplifiers

Exploiting Electrocorticographic Spectral Characteristics for Optimized Signal Chain Design: A 1.08 Analog Front End With Reduced ADC Resolution Requirements

Electrocorticography (ECoG) is an important area of research for Brain-Computer Interface (BCI) development. ECoG, along with some other biopotentials, has spectral characteristics that can be exploited for more optimal front-end performance than is achievable with conventional techniques. This paper optimizes noise performance of such a system and discusses an equalization technique that reduces the analog-to-digital converter (ADC) dynamic range requirements and eliminates the need for a variable gain amplifier (VGA). We demonstrate a fabricated prototype in 1p9m 65 nm CMOS that takes advantage of the presented findings to achieve high-fidelity, full-spectrum ECoG recording. It requires 1.08 μW over a 150 Hz bandwidth for the entire analog front end and only 7 bits of ADC resolution.

A 1024-Channel CMOS Microelectrode Array With 26,400 Electrodes for Recording and Stimulation of Electrogenic Cells In Vitro

To advance our understanding of the functioning of neuronal ensembles, systems are needed to enable simultaneous recording from a large number of individual neurons at high spatiotemporal resolution and good signal-to-noise ratio. Moreover, stimulation capability is highly desirable for investigating, for example, plasticity and learning processes. Here, we present a microelectrode array (MEA) system on a single CMOS die for in vitro recording and stimulation. The system incorporates 26,400 platinum electrodes, fabricated by in-house post-processing, over a large sensing area (3.85 × 2.10 mm²) with sub-cellular spatial resolution (pitch of 17.5 μm). Owing to an area and power efficient implementation, we were able to integrate 1024 readout channels on chip to record extracellular signals from a user-specified selection of electrodes. These channels feature noise values of 2.4 μV_rms in the action-potential band (300 Hz-10 kHz) and 5.4 μV_rms in the local-field-potential band (1 Hz-300 Hz), and provide programmable gain (up to 78 dB) to accommodate various biological preparations. Amplified and filtered signals are digitized by 10 bit parallel single-slope ADCs at 20 kSamples/s. The system also includes 32 stimulation units, which can elicit neural spikes through either current or voltage pulses. The chip consumes only 75 mW in total, which obviates the need of active cooling even for sensitive cell cultures.