The globe is being challenged by growing population and accelerated urbanization, which demands sustainable usage and sharing of resources to create more livable and smarter environments at all scales. To answer those demands, the Internet of Things (IoT) is ultimately a powerful enabler to share resources on a large scale. IoT requires pervasive sensing, which demands a large number of distributed nodes with integrated circuits to collect information. Therefore, Photovoltaic Energy Harvesters (PVEH) have been widely chosen to power IoT nodes, which minimize the maintenance costs. PVEHs are usually managed by Power Management Integrated Circuits (PMIC), also referred to as Photovoltaic cell based PMIC (PV-PMIC). One of the most important feature of PV-PMIC is Maximum Power Point Tracking (MPPT), which ensures the system can output power at Maximum Power Point (MPP). Among various MPPT algorithms, Perturb and Observe (P\&O) is the most popular, which requires measurements of a combination of current and voltage of different nodes or branches, which are analog signals and need to be converted into digital signals. To achieve this analog-to-digital conversion, many ADC and TDC architectures have been proposed, but they are all challenged by power limitation and mismatch and Process, Voltage, and Temperature (PVT) variation. This thesis aims to present the design procedure of a new type of ADC for MPPT structure in a PV-PMIC system. To achieve the objectives, a literature research is carried out, with the research question being 'Which Analog-to-Digital Conversion techniques are suitable for MPPT in a low-power, small-area chip?'. After the literature research, a set of requirements is established and an alternative ADC design is proposed and tested. The proposed design combines capacitive current sampling and a Non-Linearity Canceling TDC. The proposed design is further verified at different levels, including the system level and the circuit level. The final verification includes three tests, namely the Linear Time Response, the Static Response, and the Frequency Response. The obtained results show that the proposed system at the circuit level achieves ENOB=3.97, FoM=4.17 pJ/conv-step, DNL bounded to +-0.8 LSB, and INL bounded to 2.5 LSB. It is further concluded that the proposed system generally meets the requirements. Moreover, the proposed system has unique advantages compared to conventional ADCs for the dedicated MPPT application. Possible future improvements include further improving linearities, designing calibration and trimming methods, and replacing the hard-coded logic with a storage component.

For over five decades, electronic implants have significantly improved the quality of life for millions of patients. With their great potential, substantial advancements have been made in developing new therapeutic devices, particularly in the fields of bioelectronic medicine and brain-machine interfaces. However, these emerging devices require novel approaches to packaging, as traditional hermetic enclosures no longer meet the physical and dimensional demands of modern systems. Polymer packaging offers a promising alternative, enabling device miniaturization and facilitating minimally invasive procedures. Polymer packaging was in fact one of the earliest methods used to protect electronics (implemented with discrete components) in the body. However, due to the inability of polymers to fully block moisture ingress, it soon became evident that the body’s wet and corrosive environment could negatively impact device longevity. As electronic implants evolved from using discrete components to complex integrated circuits (ICs), the challenge of protecting these devices became even more critical. In this thesis, I aimed to tackle the challenge of ensuring the safe and reliable operation of polymerpackaged ICs for long-term implantable applications. To address this challenge, I pursued three key objectives: 1) I developed on-chip sensor platforms to carefully monitor the integrity of the IC structure. These tools provide critical data on the condition and performance of the chips, ensuring their expected functionality in clinical settings. 2) I investigated the electrical and material stability of IC structures by directly exposing them as bare die (uncoated) to physiological environments, assessing their durability in the body’s corrosive conditions. By identifying potential degradation pathways, I proposed IC design guidelines that can potentially enhance the longevity of polymerpackaged devices. 3) I investigated if silicone rubber, as a polymer packaging material, could prevent or slow down the degradations seen in uncoated ICs. Separately, I also evaluated two thin-filmpackaging layers for their effectiveness in IC protection. Results demonstrated that IC structures can be inherently hermetic, enabling polymers, such as silicone, to serve as standalone packaging materials despite their moisture permeability. Furthermore, silicone was found to effectively prevent the degradations observed in bare-die ICs. Using advanced material analysis techniques, I derived degradation rates, showing that silicone-encapsulated ICs could last over 10 years in the body. These findings enable the development of long-lasting miniature implants, reducing the need for repeated surgeries and improving patients’ quality of life.

Subjective) tinnitus is a phantom perception, where a sound is perceived by the subject that cannot be objectively perceived by other observers. an estimated 9.8% of people suffer from chronic tinnitus, moreover, for 1%-3.1% of people, it severely impacts their lives, leading to anxiety, depression, and insomnia, amongst other symptoms.
Tinnitus is strongly related to hearing loss, however, the ear is likely not the sole cause of tinnitus.

Currently, the generation and progression of tinnitus is thought to be a complex multifactorial process. Although research is ongoing and a consensus is not reached yet, the most recent theories consider the following mechanism for the development of tinnitus: (1) a lack of auditory input, triggers (2) over-expression in auditory neurons in the brainstem and auditory cortex, both part of the ascending pathway, where after (3) the tinnitus signal becomes wrongly labeled as important by the brain’s medial pathway and directed to the conscious parts of the brain where it is perceived, subsequently (4) the descending pathway is unsuccessful in suppressing the generation of tinnitus.

It is hypothesized that pairing acoustic stimulation using tinnitus-matched sound with transcutaneous electrical nerve stimulation of the vagus nerve can teach the brain to associate the distressing tinnitus sound with the de-stressing stimulation of the vagus nerve. Over time it is expected that the tinnitus sound will be labeled as unimportant by the medial pathway and is thus consequentially suppressed.

To investigate this hypothesis a bimodal stimulator is required that can combine acoustic stimulation and transcutaneous electrical vagus nerve stimulation. The device should be easy to use and safe. The specific focus of this thesis report was to design the electronic hardware for electrical stimulation and power management and implement various safety features.

From testing the stimulation output it could be concluded that the device is successfully able to produce the electrical pulse pattern and potentially any other electrical pattern. Following a risk assessment, and analyzing the safety of the device, it was concluded that the device can be used to test the efficacy of the proposed treatment, given that it is used in the prescribed circumstances and that the user is aware of the risks. Furthermore, it was shown that the device was able to stimulate the vagus nerve. Overall, the device was easy to use and was able to pair acoustic and electrical stimulation.

The recording of biosignals, such as atrial electrograms (AEG), electrocardiograms (ECG), and electroencephalograms (EEG), is progressing towards the adoption of more dense electrode arrays in order to improve spatial and temporal resolution. The proliferation of channels necessitates some form of channel sharing technique so that efficient low power and area recording can be achieved.
In this thesis, a code-division multiplexed analog front-end is designed due to its efficient use of bandwidth in comparison to time and frequency multiplexing. Orthogonal coding schemes such as Walsh-Hadamard sequences are best suited for minimising cross-talk. These codes are typically implemented using an LUT or processor which becomes a significant overhead when a large number of channels are to be multiplexed. However, by investigating the sequences closely, a novel method of generating these codes from a clock signal using digital logic was devised. The proposed algorithm to generate these sequences on-chip provides significant area savings for sequences of length greater than 8, which makes the design scalable for a large number of channels,. The reduction in area ranges from a factor of 10 for a code length of 8 up to a factor as large as 200 for a code length of 128.
As orthogonal sequences require a low bandwidth, a low bandwidth low-noise amplifier and ADC were used for amplification and digitisation of the signal. By using digitally inspired analog blocks, such as an inverter-based amplifier, lower power consumption could be achieved.
The entire design was implemented to share 7 channels. The code generator, low-noise amplifier and ADC consume a total of 78.4μW, which corresponds to 11.2μW per channel. This is a 3.3x improvement to the design in [5] where pseudo-random sequences were used as the coding scheme. However, the design consumes more power than a state-of-the-art design reported in [6] which uses 1.97μW per channel. While the design is currently not optimized with respect to power consumption in comparison to the design in [6], the novel code generation technique reported in this thesis makes the design scalable for larger number of channels. This is because the area constraint of the LUT is no more the limiting factor in terms of area.

This study aims to systematically design and implement a voltage regulation control loop (VRCL) for an unspecified power management unit (PMU) to maintain the desired load voltage for electronics worn by group-housed rodents. This is crucial for analyzing the spontaneous behaviour of group-housed rodents, focusing on social interactions and environmental exploration in a simulated natural environment.

The study explores a potential high-level design of a power link, selecting resonant inductive coupling for wireless power transfer (WPT), enabling continuous power supply over larger areas (for instance, 5 by 5 meters). A literature review reveals a research gap in integrating encircling and underneath configurations for sufficient uniform power distribution. A block diagram of the WPT system is provided, outlining the transmitter and headstage receiver components. Subsequently, a hybrid layout is suggested and significant challenges like optimizing driving current and minimizing angular and vertical misalignments are addressed.

Next, a control loop is systematically designed and implemented. Potential loads and a PMU are
selected, followed by the development and verification of an ideal power converter and its derived
and proposed plant model. Control specifications derived from this model suggest the tuning of the
controller parameters using a tailored model-based control system approach. MATLAB simulations
confirm that the control specifications are met. A non-ideal power converter is then integrated with the control loop, including ideal gate drivers, a voltage-controlled oscillator, a bandgap reference, and a PI controller. Simulation results show that the control loop meets the specifications. Despite limitations in robustness, particularly regarding load and input voltage transient response, the study also highlights the need for verification of the power converter model for load capacitors in the pF-nF range, and identifies discrepancies in overshoot behaviour. Future work includes an analysis of the system’s robustness during controller tuning and the incorporation of a transient controller. The combination of the suggested plant model and model-based tuning approach offer an alternative option for the power converter’s control loop design.

Cervical Vagus Nerve Stimulation (CVNS) has shown efficacy in treating depression, therapy-resistant epilepsy, and is being explored for conditions such as obesity and migraine. The side effects of whole nerve stimulation, which is currently the only approved method, can be minimized using spatially selective stimulation. This thesis introduces Temporal Current Steering (TCS), a novel stimulation technique aimed at enhancing spatial selectivity for CVNS. TCS introduces a temporal variation to standard current steering, creating an electric field that varies both temporally and spatially. With this study, enhanced spatial selectivity was confirmed through simulations of extracellular stimulation of neurons with time-dependent waveforms on two electrodes located on a single plane. Particle swarm optimization was employed over 2000 iterations and 98 runs to identify a waveform with the highest spatial selectivity. The optimal solution achieved a 30% improvement over a single electrode placed directly in line with the target and a 31% improvement over the standard direct current steering technique, simulated in the same model. The findings of this thesis suggest that TCS can increase spatial selectivity in invasive stimulation, although further simulations are needed for non-invasive applications with greater electrode-to-neuron distances.

Subjective tinnitus is a sensation of sound without an external source. There is no clear understanding of the cause and pathology of tinnitus.

Literature suggests a combination of deafferentation of the tonotopic map , the Bayesian brain model, and the triple mode network, creating one combined hypothesis for tinnitus pathology. Based on the combined hypothesis, transcutaneous vagus nerve stimulation paired with tinnitus-matched sound stimulation should train the brain to reduce the tinnitus sound's importance, thereby eliminating it from conscious awareness.

To investigate this hypothesis in clinical studies, a device that combines transcutaneous electrical nerve stimulation on the tragus with tinnitus-matched sounds in the ears is needed. The device should be easy to use and electrically safe.

A device has been designed with a user interface that interacts with a microcontroller, following the requirements. The microcontroller controls the audio stimulation shield and the custom-made stimulation circuit designed by Jonathan Kneepkens.

Electrical stimulation of the tragus provides the right effect. It activates the parasympathetic nervous system. The device's efficacy as a treatment must await clinical trials with patient-specific tinnitus-matched acoustical stimulation.

Neurological disorders profoundly affect quality of life, impairing essential functions like memory, cognition, and movement. Traditional treatments are often limited due to the complexity of the brain, the invasiveness of procedures, or the poor precision of the treatment. Ultrasound (US) neuromodulation offers a promising and minimally invasive alternative, using ultrasound waves to modulate neural activity in deep brain regions with high spatial resolution. Despite its potential, a technological gap limits preclinical ultrasound neuromodulation studies, as current ultrasound devices are too bulky and imprecise for flexible and continuous neuromodulation in freely moving rodents. Moreover, precise targeting is essential for effective neuromodulation, necessitating fine control over the focal spot location. This thesis aims to discover new system-level and circuit-level approaches to designing a miniaturized, power-efficient, and high-spatial-resolution 2D phased array transmitter application-specific integrated circuit (ASIC). These approaches are guided by the vision of implementing a miniaturized ultrasound transducer device for precise ultrasound neuromodulation in freely moving rodents, ultimately laying the foundation for future clinical applications in neurological disorder treatment.
The thesis begins with a literature review to determine the acoustic parameters required for effective ultrasound neuromodulation. Then, a comprehensive system-level study using the k-Wave Matlab toolbox is conducted, examining factors critical to the design of a 2D phased array transducer. This study highlights how parameters such as driving voltage, phase quantization resolution, frequency, and array length significantly impact the performance of the 2D phased array ultrasound transducer by influencing key acoustic and electrical attributes. Optimizing these parameters is essential to achieving high focal gain and spatial resolution while minimizing power consumption. The study finds that a three-bit phase resolution is optimal for accurate ultrasound beam steering. Additionally, while increasing array length improves spatial resolution and phased array gain, it also increases the overall size of the ultrasound transducer, constrained by the small brain sizes of rodents in preclinical studies. This study demonstrates that higher frequencies enhance spatial resolution and phased array gain. However, due to kerf limitations in the dicing manufacturing process of piezoelectric transducers, increasing frequency reduces the effective area of the transducers. Moreover, the pitch size should be reduced with increasing frequency in order to avoid the appearance of the grating lobes in the beam profile, forming a tradeoff between the frequency and the available area for the beamforming channels. Since higher frequencies are desired, particularly for applications in which higher spatial resolution is needed, high-voltage beamforming channels have been developed to investigate the highest frequency that allows for implementing a high-voltage beamforming channel. In this regard, two beamforming channels have been implemented and validated in TSMC 180-nm BCD technology, allowing for driving the ultrasound transducers with 12-MHz 36-V pulses. On the other hand, the power consumption of the beamforming channels has a crucial impact on the overall power efficiency of the ASIC. Therefore, a power-efficient HV pulser is developed, leading to 40.9% power consumption reduction with respect to the conventional HV pulser.
Utilizing the proposed beamforming channels, a prototype 2D phased array transmitter ASIC is developed to validate the findings of the initial system-level study. The transmitter ASIC includes a 12*12 array of beamforming channels that generate 12-MHz pulses with 20-V amplitude. The phasing circuitry in the ASIC generates the required delay for each beamforming channel, hence allowing the ASIC to steer the ultrasound beam. The measurement results proved the functionality of the phased-array transmitter ASIC in terms of phase quantization, showing a maximum DNL of 0.35 LSB. Furthermore, the ASIC allows for controlling the driving voltage and the burst duration, as needed for US neuromodulation applications. Based on the prototype 2D phased array transmitter ASIC, a US-guided US transmitter ASIC is developed for preclinical US neuromodulation experiments in freely moving rats. Considering the size of the rat's brain, the size of the ASIC is limited to 5*5 mm2. Given the prior discussion, the frequency was set to 12 MHz to achieve higher spatial resolution and phased array gain. Taking into account the proposed 20-V beamforming channel, the size of the 2D array was set to 66*66. According to the author's knowledge, this is the first transmitter ASIC that allows for preclinical US neuromodulation experiments on freely moving animals. Moreover, a temperature sensor was added to the ASIC to monitor the temperature rise in the ASIC. In order to monitor the location of the focal spot during the US neuromodulation, synthetic aperture US imaging capabilities are added to the ASIC to track the tissue displacement caused by the US neuromodulation push. In this regard, the ASIC includes eight groups of receiver channels that will be connected to 96 piezoelectric transducers using an analog multiplexer. To prevent side lobes in the beam profile, a system-level study was conducted to determine the optimal placement of receiver channels within the 2D array. The study revealed that a random distribution of receiver elements among the 2D transmitter elements is the most effective arrangement for minimizing side lobe appearance. To the best of the author's knowledge, this is the first ultrasound neuromodulation ASIC with integrated imaging capabilities. The measurement results proved the functionality of the ASIC in generating 20-V 12-MHz pulses with a programmable burst duration. The simulation results have shown that the receiver channels are capable of recording the echoes required for US imaging to monitor the location of the focal spot.
In summary, this thesis describes innovations in system-level and circuit-level integrated circuit design for developing an ultrasound ASIC that can be integrated with a 2D array of piezoelectric transducers, forming a miniaturized phased array US transducer that allows 3D US beam steering and focusing with the highest combination of spatial resolution and penetration depth in the context of pre-clinical studies. The ASIC includes the receiver channels that can be used for US imaging, allowing for monitoring real-time monitoring of the location of the focal spot during the US neuromodulation. This US ASIC leads to the emergence of miniaturized US transducers compatible with preclinical behavioral experiments in rodents, paving the way for the development of therapies to treat neurological disorders in humans.

Technologies that are employed to record and modulate neural activities are rapidly advancing. This advancement could bring breakthroughs in our understanding of brain function and enable scientists to diagnose and treat neural diseases and disorders. Combining multiple modalities to study brain function, from single cells to large networks, offers insights beyond those offered by a single-modal platform using only electrical recording or modulation. However, the tools to enable such studies are yet to be developed and still face significant challenges that remain to be resolved to allow multimodal measurement without any of the modalities interfering with one another.
Recently, graphene-based neural electrodes have shown great promise for combining optical and electrical modalities in a single device. However, their complicated fabrication process, high impedance, and low charge storage capacity currently limit their application. In addition, their compatibility with the magnetic domain remains to be proven.
In this thesis, graphene-based microfabricated platform technology is introduced for the manufacturing of multimodal neural interfaces. First, a transfer-free fabrication process is demonstrated to fabricate multilayer graphene electrodes on parylene-C substrates. Full electrochemical characterization is performed on these graphene electrodes and a comparison is made with conventional metal-based electrodes. Second, a nanoparticle printing technique, spark ablation, is leveraged to print platinumnanoparticles on the graphene electrode surface to enhance its electrochemical characteristics even further without compromising its optical transparency. Third, a hybrid encapsulation stack is fabricated and validated that includes parylene C and PDMS with thin ceramic interlayers to be employed as the encapsulation layer on the final neural-interface device.
The multimodal platform technology introduced in this thesis can be used as a tool inmultimodal measurements combining electrical, optical, and magnetic domains. The fabricated multilayer graphene electrodes showthe highest charge storage capacity among all CVD graphene electrodes to date. They show no optical and MRI artifacts. Moreover, the fabricated electrodes and encapsulation stack both reveal the high optical transparency required for optical measurements. Local platinum nanoparticle printing can improve the impedance, charge storage, and charge injection capacity by 4.5, 15, and 3.6 times, respectively.

Class D amplifiers find widespread application in audio devices for driving load speakers, primarily due to their remarkable efficiency. Nonetheless, this enhanced efficiency often comes at the expense of reduced linearity. Hence, techniques for reducing Total Harmonic Distortion (THD) are important in the context of class D amplifiers.

The analysis of the distortion mechanisms is first presented. Specifically, emphasis is placed on the distortion generated within the power stage, encompassing aspects such as deadtime distortion and rising and falling time distortion. Both of them are found to be related to the input signal. Subsequently, the compensation technique is applied to the conventional class D amplifier to reproduce and cancel the error. The idea of the compensation approach involves modifying the amplitude of the triangular waveform based on the input signal. A 12 dB THD improvement is achieved in the concept verification section, which is conducted in LTspice.

The negative feedback serves as another technique to achieve THD reduction. A straightforward two-step design methodology is presented to avoid design iterations in the concept design phase. The phantom zero technique is applied when doing the frequency compensation of the feedback loop. The validation of the concept is performed through the use of SLICAP, while the circuit implementation and simulations are carried out within Cadence. Remarkably, this technique results in an impressive -111.8 dB THD reduction, achieved when the output power equals 1 W.

Electrical stimulation has emerged as a promising therapeutic modality for the treatment of various neurological disorders such as Parkinson's disease, chronic pain, epilepsy, and depression. In addition, recent studies have provided evidence supporting the effectiveness of electrical stimulation as a treatment option for patients with chronic migraine and cluster headaches who have been unresponsive to other therapies. Specifically, stimulation of the occipital and supraorbital nerves has shown promise in managing these refractory conditions. Current implantable medical devices (IMDs) are battery-powered, which increases the size of the implant and involves lengthy wires to connect with the electrodes. Wireless power transfer (WPT) techniques can be used to reduce the size and omit the battery from the implants. However, conventional power management methods use a rectifier, power converter, and neurostimulator to convert the AC power of the link to DC power and provide electrical stimulus, which lowers implant power efficiency.

This thesis presents a novel neurostimulator circuit that salvages and stores available energy from an inductive link. The circuit design includes an inductor for energy storage and utilizes a buck-boost converter-like topology to deliver the stored energy to the tissue. This topology exploits the capacitive membrane's characteristics and injects the charge into the tissue through ultra-high frequency pulsed stimulation without requiring additional circuits that may contribute to power losses. Operating at the resonance frequency of 6.58MHz, the circuit was designed and simulated to inject approximately 500nC at an 18mm distance from the transmitter. Furthermore, the proposed circuit design incorporates a charge-metering circuit adapted to ensure stimulation efficacy in response to coupling variations. To guarantee safety during stimulation, the residual voltage is carefully monitored and brought close to zero at the end of each stimulation cycle. To achieve this, a charge-balancing scheme has been implemented, which utilizes a comparator to monitor the residual voltage across the electrode.

The proposed circuit was designed on a printed circuit board (PCB) to evaluate its feasibility. To evaluate its performance, a signal generator was used to simulate the input of the inductive link, and an electrode-tissue interface (ETI) model was used at the output. The circuit demonstrated its efficacy in measuring the charge and reducing the residual voltage within established safety limits while maintaining energy efficiency. More specifically, the charge metering measured a charge of 404nC for 450nC of injected charge, which is a 10.22% of error. Moreover, the circuit exhibited a linear response in controlling the injected charge. In the tested range, the charge balancing scheme yielded residual voltages ranging from -20mV to -16mV. The effectiveness of the charge balancing scheme was further confirmed through in-vitro measurements in a phosphate-buffered solution, with residual voltages measuring at -20mV, which falls within the safe range. Finally, the implemented circuit achieved a peak efficiency of 56%.