Integrated Signal Demodulation, Data Conversion, and Packaging Strategies for a Wireless, Fully Implantable, Bidirectional Neural Interface

Over the past decades, an important area within bioengineering has focused on restoring lost physiological function in humans. Among the various application domains, one of the most relevant is the development of upper-limb prostheses to replace missing limbs following amputation. Neural prosthetics represents a promising research direction, with the potential to substantially improve the quality of life of amputees. Unlike commercial prostheses, which are typically controlled through EMG signals and therefore provide limited and unnatural control with no sensory feedback, neural prostheses aim to overcome these limitations by using the same implanted electrodes both for motor control and for restoring a sense of touch. This thesis presents contributions to the development of a fully implantable, bidirectional, wireless neural interface intended for neuroprosthetic and bioelectronic applications. The system, conceived within a broader collaborative project, consists of an inductively powered implantable hub and an external unit fabricated in 180nm CMOS technology, enabling wireless power transfer and both low- and high-bitrate data communication links. The implantable platform distributes power and data to multiple distributed recording and stimulation front-ends. Within this framework, the thesis focuses on the design and implementation of mixed-signal and packaging blocks required for the implantable platform. A compact demodulation and decoding scheme for the wired interface between the implantable hub and the distributed neural front-ends is presented, enabling simultaneous power and data trans- mission over a four-wire connection through amplitude-modulated clock encoding. The thesis further addresses low-power neural signal acquisition by developing an analog-to-digital conversion scheme that initially follows the Wilkinson architecture, in which the input sample is first converted into a time interval by measuring the discharge time of a capacitor, and this interval is subsequently digitized by a time- to-digital converter (TDC). The TDC is implemented using a two-phase conversion scheme with temporal amplification via current-starved ring oscillators, enabling a significant reduction in clock frequency and energy consumption while maintaining the required resolution for neural recording. Furthermore, the thesis contributes to the early-stage development of a high-density hermetic feedthrough fabrication process using unsintered HTCC and screen-printed platinum, laying the technological groundwork for miniaturized, biocompatible interconnects in implantable packaging.