A Bidirectional Neural Interface SoC With Adaptive IIR Stimulation Artifact Cancelers.

We present a 180-nm CMOS bidirectional neural interface system-on-chip that enables simultaneous recording and stimulation with on-chip stimulus artifact cancelers. The front-end cancellation scheme incorporates a least-mean-square engine that adapts the coefficients of a 2-tap infinite-impulse-response filter to replicate the stimulation artifact waveform and subtract it at the front-end. Measurements demonstrate the efficacy of the canceler in mitigating artifacts up to 700 mVpp and reducing the front-end amplifier saturation recovery time in response to a 2.5 Vpp artifact. Each recording channel houses a pair of adaptive infinite-impulse-response filters, which enable cancellation of the artifacts generated by the simultaneous operation of the 2 on-chip stimulators. The analog front-end consumes 2.5 µW of power per channel, has a maximum gain of 50 dB and a bandwidth of 9.0 kHz with 6.2 µVrms integrated input-referred noise.

A portable multi-sensor module for monitoring external ventricular drains.

External ventricular drains (EVDs) are used clinically to relieve excess fluid pressure in the brain. However, EVD outflow rate is highly variable and typical clinical flow tracking methods are manual and low resolution. To address this problem, we present an integrated multi-sensor module (IMSM) containing flow, temperature, and electrode/substrate integrity sensors to monitor the flow dynamics of cerebrospinal fluid (CSF) drainage through an EVD. The impedimetric sensors were microfabricated out of biocompatible polymer thin films, enabling seamless integration with the fluid drainage path due to their low profile. A custom measurement circuit enabled automated and portable sensor operation and data collection in the clinic. System performance was verified using real human CSF in a benchtop EVD model. Impedimetric flow sensors tracked flow rate through ambient temperature variation and biomimetic pulsatile flow, reducing error compared with previous work by a factor of 6.6. Detection of sensor breakdown using novel substrate and electrode integrity sensors was verified through soak testing and immersion in bovine serum albumin (BSA). Finally, the IMSM and measurement circuit were tested for 53 days with an RMS error of 61.4 µL/min.

A Chopper-Stabilized, Current Feedback, Neural Recording Amplifier.

Advanced neural prosthetics requires high density neural recording and stimulation electrodes interfacing with the tissue. For an implantable device, area, power consumption, and noise performance are the key design metrics. Due to the low-frequency nature of the recorded signals, chopping technique is inevitable to satisfy the noise requirement while maintaining a small area and low power consumption. However, chopping leads to a significant drop in input impedance, which leads to potential attenuation of neural signals recorded from high impedance miniature electrodes, and an unacceptable large input current drawn from the tissue. This work presents a chopper stabilized, current feedback amplifier (CFA) with input impedance boosted to 3.0 GΩ. The amplifier has an adjustable voltage gain of 40-60 dB, and an adjustable high-pass cut-off frequency of 0.5 - 5 Hz, with a power consumption of 2.6 µW and noise efficiency factor (NEF) of 3.2.