This article presents a wireless neuromodulation headstage prototype intended for in-vitro recording and stimulation in freely behaving mice. The prototype allows independent stimulation on 32 channels and can record up to 32channels in the local field potential (LFP) band, while the simultaneous recording in the action potential (AP) band is limited to 3 channels when data is not compressed. All recorded data is directly streamed via Bluetooth Low Energy (BLE), enabling immediate analysis during the experiment. The small size of 20x24 x8 mm and a low total weight of 3.9g makes this neurologger suitable to be used on small rodents such as mice. A moderate power consumption of 29.3mW for 32channel recording and transmission of LFP band data ensures a long uninterrupted operation of almost 5hours.

Stimulation waveforms and artifacts can exceed the neural signal of interest by several orders of magnitude, thus requiring blanking switches to avoid saturation of the front-end and extensive subsequent recorder blind-time during the recovery. Several recent publications propose to instead utilize recording front-ends with high dynamic range, however typically at the cost of reduced first-stage gain and an adversely affected noise efficiency factor. Recently, we have demonstrated a combination of blanking switches and a tuning mechanism for the pseudo-resistor based high-pass corner frequency in a recorder to achieve rapid artifact recovery by temporarily increased settling speed. In this article, we extent this by an in-depth analysis and significantly improve the artifact recovery abilities by utilizing a combination of passive electrode discharge and recorder reset, thereby improving the recovery time after stimulation significantly, to less than 10in spike recordings with maximum gain setting of 70. The measurements are conducted with a new hardware platform, and extensive in-vitro verification is provided to demonstrate the feasibility of the combined artifact recovery.

This paper presents an extensive study of pseudo-resistors for usage in biomedical applications like implantable brain-machine-interfaces. In order to suppress DC offsets while simultaneously recording signals ranging into the sub-hertz domain, low-frequency high-pass filters are employed in the frontend of neural recording integrated circuitry. With the limited ranges of on-chip passives, no sub-hertz corner frequencies are possible. Switch-capacitor resistances and resistor duty-cycling are infeasible since these techniques cannot provide the required absolute resistance values. Concepts like multi-rate duty-cycled resistors have been successfully demonstrated, but require clock signals, which can lead to noise back-folding, especially in chopped systems. Pseudo-resistors utilize the off-resistance of MOSFETs to form extraordinary large resistors, and are thus capable of providing the required corner frequency in a very area efficient way. The drawbacks are limited linearity, and deviations of 100x over process variation and temperature were reported in prior art. In this brief we show measurement results from more than 160 dice (>5400 recording channels) from 3 production runs to demonstrate that the variations are much less severe in realistic operating conditions, and that sufficient linearity can be achieved. Our experiments let us conclude that the usage of pseudo-resistors in neural recording applications can in fact be used to robustly realize the required HP corner frequency for electrode DC offset blocking.