Implantable Medical Devices (IMDs) have been widely used to tackle different health issues. With the advancement in VLSI technology, sophisticated IMDs have been developed for extending sensing and stimulation capability with low-power wireless data transmissions. The first part of this thesis studies the power-delivering capability of a Class-D power amplifier at different operating conditions when driving either a series-series or a series-parallel (transmitter (Tx) - receiver (Rx)) resonant tank of a wireless power transfer (WPT) system. The accuracies between analytical and simulated results and between analytical and measured results are better than 98% and 95%, respectively.

Due to loading and coupling variations, the rectified DC voltage at the receiver’s output of the IMD is no...[ Read more ]

Implantable Medical Devices (IMDs) have been widely used to tackle different health issues. With the advancement in VLSI technology, sophisticated IMDs have been developed for extending sensing and stimulation capability with low-power wireless data transmissions. The first part of this thesis studies the power-delivering capability of a Class-D power amplifier at different operating conditions when driving either a series-series or a series-parallel (transmitter (Tx) - receiver (Rx)) resonant tank of a wireless power transfer (WPT) system. The accuracies between analytical and simulated results and between analytical and measured results are better than 98% and 95%, respectively.

Due to loading and coupling variations, the rectified DC voltage at the receiver’s output of the IMD is not steady. Conventionally, a global control loop that combines the power and data transfer links is designed to counteract the above variations. A detection (or tertiary) coil, co-planar with the transmitter coil, is used to receive the backscattered signal at the transmitter side. The second part of this thesis discusses the improvement of a previously designed retinal implant. In the first phase, a framework is designed for improving the tertiary coil through analytical guidelines, and an area-saving inner-tertiary coil structure is developed for a closely packed head-mounted retinal stimulation system. In the second phase, an on-chip embedded encrypted data transmission system is developed using lightweight prince cipher and eFUSE silicon IP provided by the foundry. The standalone eFUSE IP is modified to relax input pin limitations and high current consumption issues during the initialization of the IMD. The proposed divide-and-conquer approach maintains the cipher strength and reduces the area and power consumption of the cipher circuits by 2.7 and 5.1 times, respectively. The whole system with the optical nerve stimulator is fabricated with 0.18μm BCDlite (Bipolar-CMOS-DMOS) process, and measurement results show the proposed encryption scheme is nearly impossible to be cracked by a modern brute-force parallel key-guessing machine.

In the third part of this thesis, a complete WPT system with transmitter and receiver chips developed in 0.18μm BCDlite is presented. The all-NMOS transmitter has fast high-side level shifters based on the current mirror principle and adaptive dead-time controller, reduces the delay difference between the high-side and low-side gate driving paths. The proposed adaptive digitally controlled active rectifier of the receiver achieved high efficiency by eliminating losses due to turn-on/off delay, reverse current, and multiple pulsing. The adaptive delay compensation circuits prevent efficiency and link gain degradation at different PVT (process, voltage, temperature) corners. The fast delay control loop adjusts the durations of delay by at least two times faster than state-of-the-art architectures. In closed-loop control of the WPT system, the receiver regulates the output voltage using a local linear current-sink-based regulator. In addition, wireless hysteretic control of a reconfigurable power amplifier achieves global power regulation. The proposed design has a higher level of integration and lower circuit complexity than previous works and achieves a higher operating range and a faster load-transient response. Furthermore, under high coupling conditions, split frequency locations can be used for FSK-based closed-loop control that allow for simultaneous wireless power and data transfer. The frequency-modulated power carrier is processed by a frequency-to-amplitude converter of the receiver and is converted to an amplitude-modulated signal. A rule-based approach is adopted in discussing the trade-off among link gain, bandwidth, and efficiency as a function of distance during split-frequency data transfer.