To achieve greater specificity in neurostimulation, bidirectional neural interfaces are required to verify the recorded neural response after stimulation. The specific neural interface targeted in this thesis is the epiretinal implant. Due to the heterogeneity of the retinal ganglion cells (RGCs), high-fidelity vision is only possible when all the types of RGCs near the neurostimulator are mapped. This necessitates the bidirectionality of the implant and poses significant difficulties, as large stimulation artifacts obscure the small neural response that needs to be recorded. Furthermore, in order to cover a large area of the retina, a channel count in the order of 104 will be required. Scaling existing neurostimulators would lead to chips that are >30mm2, which is too large. The aim of this thesis is therefore to design a neurostimulator for the epiretinal implant that is capable of implementing artifact-reducing algorithms, and is smaller than the current state-of-the-art. The proposed system makes use of a mismatch-based digital-to-analog converter (DAC), and has been optimized for an output range of 0-6 μA at an effective resolution of 8-bits. Furthermore, in order to decrease the amount of stimulation units required, waveform interleaving has been proposed, where the anodic and cathodic stimulator are separated. A voltage compliance monitor is also designed to ensure proper stimulation output. The designed system has been fabricated and occupies 0.0003mm2 for two channels. Scaling this directly to 104 channels would result in an area of 1.645mm2. This area can be reduced even further via electrode multiplexing, which the designed system readily allows for. An output availability (i.e. how many input codes are possible after calibrating) of 99.2% and 97.3% is reported for the anodic and cathodic stimulator at an 8-bit resolution over the full output range.

To enable the portable use of electronic devices, (rechargeable) batteries need to be used. These batteries require a battery management system in order for them to operate safely and efficiently. This thesis describes such a system for the Wireless Powerlizer: a power bank with wireless charging capabilities and an integrated sterilizer using UV-C light. The battery management system comprises of a charging circuit, a protection module, and cell balancing features. These features are designed to function with Li-ion batteries, which are chosen for their high volumetric energy density, in a 5S1P configuration. These batteries will be charged via a constant-current, constant-voltage (CC-CV) scheme in order to improve charging speed. This charging scheme will be facilitated by a DC-DC boost converter with current and voltage control. The mechanism behind the protection module (overcharge, overdischarge, overcurrent, and temperature) and passive cell balancing features are elucidated via flowcharts and also verified by simulation in Simulink. A prototype encompassing the charging circuit is implemented on a PCB and tested. The realized boost converter successfully allows for CC-CV charging: it operates at 263kHz, has a charging current of 1A, a constant voltage boundary of 19.6V, and shows an efficiency of 92—93.6%.