Implantable microelectronic devices (IMDs), specifically the retinal/cochlear prostheses and the brain-machine interfaces, have gained great breakthroughs in the past decade. Sensations are restored for vision/hearing-impaired or spinal-cord injured people by these IMDs accordingly. Such devices require miniaturized form factor, real-time and high-efficiency wireless power transfer in the range of 10 to 100 mW. In this thesis, power management integrated circuits (PMIC) designed for IMDs are introduced in two parts: (1) wireless power acquisition and (2) regulation.

Inductively coupled (near-field) wireless power transfer is commonly used to power up the IMDs, for the reasons of high efficiency and low human tissue specific absorption rate (SAR) comparing to far-field power tra...[ Read more ]

Implantable microelectronic devices (IMDs), specifically the retinal/cochlear prostheses and the brain-machine interfaces, have gained great breakthroughs in the past decade. Sensations are restored for vision/hearing-impaired or spinal-cord injured people by these IMDs accordingly. Such devices require miniaturized form factor, real-time and high-efficiency wireless power transfer in the range of 10 to 100 mW. In this thesis, power management integrated circuits (PMIC) designed for IMDs are introduced in two parts: (1) wireless power acquisition and (2) regulation.

Inductively coupled (near-field) wireless power transfer is commonly used to power up the IMDs, for the reasons of high efficiency and low human tissue specific absorption rate (SAR) comparing to far-field power transmission. Three high-efficiency active rectifiers (AC-to-DC power converters) are designed, fabricated with standard 0.35 μm CMOS process, and measured with inductively coupled PCB air coils. The four diodes of a conventional passive rectifier are replaced by two cross-coupled PMOS transistors and two comparator-controlled NMOS switches to eliminate diode voltage drops such that high voltage conversion ratio could be achieved even at low AC input amplitude lV_ACl. The comparators are implemented with switched-offset biasing to compensate for the delays of active diodes and to eliminate multiple pulsing and reverse current. The first rectifier uses a CMOS peaking current source to obtain a bias current that is insensitive to the change in lV_ACl. The second and improved rectifier uses a modified CMOS peaking current source with bias current that is quasi-inversely proportional to the supply voltage (QIPV) to better control the reverse current over a wide AC input range (1.5 to 4 V). The third rectifier also employs the novel QIPV bias circuit, and is equipped with reconfigurable 1X or 2X modes for extended-range wireless power transmission. The active rectifiers process the converted magnetic power efficiently to DC electrical power, and constitute the input part of the PMICs for implants.

Since the coupled lV_ACl may change by a couple of times due to relative movements (distance and/or orientation) between the primary and secondary coils, the rectifier DC output voltage would change substantially. Besides, different regulated supply voltages are needed for various functional blocks. For example, the microelectrode may need 2 to 10 V depending on the tissue impedance that is being stimulated; and 1 V is needed for digital and low-power circuits. To improve the overall efficiency, a novel dual-output charge pump (DOQP), consists of one step-down output and one step-up output with variable voltage conversion ratios, is inserted between the rectifier and the low-dropout (LDO) regulator. In addition to the charge pump, an ultra-fast response fully integrated LDO regulator with full spectrum power supply rejection is proposed to improve the performance of noise-sensitive building blocks, such as the RF receiver, the voltage and/or frequency references.