Inductive Power Link for a Wireless Cortical Implant with Biocompatible Packaging

This article presents an inductive power link for a cortical implant. The link includes a Class-E power amplifier, an inductive link, a matching network, and a rectifier. The coils of the inductive link are designed and optimized for a distance of 10mm (scalp thickness). The power amplifier is designed in order to allow closed loop power control by controlling the supply voltage. A new packaging topology is proposed in order to position the implant in the skull, without occupying much area, but still obtaining short distance between the remote powering coils. The package is fabricated using biocompatible materials such as PDMS and Parylene-C, and it includes the secondary coil, the matching network, and the rectifier. The power efficiency of the link is characterized for a wide range of load power (1-20mW) and found to be 8.1% for nominal load of 10mW. The matching network improves the power efficiency on the whole range, compared to the link without the matching network

A fully on-chip LDO voltage regulator with 37 dB PSRR at 1 MHz for remotely powered biomedical implants

This article presents a fully on-chip low-power LDO voltage regulator dedicated to remotely powered wireless cortical implants. This regulator is stable over the full range of alternating load current and provides fast load regulation achieved by applying a time-domain design methodology. Moreover, a new compensation technique is proposed and implemented to improve PSRR beyond the performance levels which can be obtained using the standard cascode compensation technique. Measurement results show that the regulator has a load regulation of 0.175 V/A, a line regulation of 0.024%, and a PSRR of 37 dB at 1 MHz power carrier frequency. The output of the regulator settles within 10-bit accuracy of the nominal voltage (1.8 V) within 1.6 μs, at full load transition. The total ground current including the bandgap reference circuit is 28 μA and the active chip area measures 290 μm × 360 μm in a 0.18 μm CMO

Load optimization of an inductive power link for remote powering of biomedical implants

This article presents the analysis of the power efficiency of the inductive links used for remote powering of the biomedical implants by considering the effect of the load resistance on the efficiency. The optimum load condition for the inductive links is calculated from the analysis and the coils are optimized accordingly. A remote powering link topology with a matching network between the inductive link and the rectifier has been proposed to operate the inductive link near its optimum load condition to improve overall efficiency. Simulation and measurement results are presented and compared for different configurations. It is shown that, the overall efficiency of the remote powering link can be increased from 9.84% to 20.85% for 6 mW and from 13.16% to 18.85% for 10 mW power delivered to the regulator, respectively

MEMS dönüölçerler için yüksek performanslı CMOS sığasal arabirim devreleri.

This thesis reports the development and analysis of high performance CMOS readout electronics for increasing the performance of MEMS gyroscopes developed at Middle East Technical University (METU). These readout electronics are based on unity gain buffers implemented with source followers. High impedance node biasing problem present in capacitive interfaces is solved with the implementation of a transistor operating in the subthreshold region. A generalized fully differential gyroscope model with force feedback electrodes has been developed in order to simulate the capacitive interfaces with the model of the gyroscope. This model is simplified for the single ended gyroscopes fabricated at METU, and simulations of resonance characteristics are done. Three gyroscope interfaces are designed by considering the problems faced in previous interface architectures. The first design is implemented using a single ended source follower biased with a subthreshold transistor. From the simulations, it is observed that biasing impedances up to several gigaohms can be achieved. The second design is the fully differential version of the first design with the addition of a self biasing scheme. In another interface, the second design is modified with an instrumentation amplifier which is used for fully differential to single ended conversion. All of these interfaces are fabricated in a standard 0.6 m CMOS process. Fabricated interfaces are characterized by measuring their ac responses, noise response and transient characteristics for a sinusoidal input. It is observed that, biasing impedances up to 60 gigaohms can be obtained with subthreshold transistors. Self biasing architecture eliminates the need for biasing the source of the subthreshold transistor to set the output dc point to 0 V. Single ended SOG gyroscopes are characterized with the single ended capacitive interfaces, and a 45 dB gain improvement is observed with the addition of capacitive interface to the drive mode. Minimum resolvable capacitance change and displacement that can be measured are found to be 58.31 zF and 38.87 Fermi, respectively. The scale factor of the gyroscope is found to be 1.97 mV/(°/sec) with a nonlinearity of only 0.001% in ±100 °/sec measurement range. The bias instability and angle random walk of the gyroscope are determined using Allan variance method as 2.158 °/√hr and 124.7 °/hr, respectively.M.S. - Master of Scienc

Remotely Powered Wireless Cortical Implants for Brain-Machine Interfaces

Brain-machine interfaces hold promise for restoring basic functions such as movement or speech for severely disabled patients, as well as for controlling neuroprosthetic devices for amputees. One of the major challenges of clinically viable neuroprostheses for chronic use is the implementation of fully implantable recording devices for stable, long-term recordings over large populations of neurons. Recent progress in the microelectronics and MEMS technologies has enabled miniaturization of microelectrode arrays which can be used for recording the neural activity of the brain and for stimulating the neurons. Nevertheless, the demanding requirements of fully implantable recording devices necessitate the incorporation of other active components with the microelectrodes. The presence of the active components in the implant requires power to be delivered to the device. Transcutaneous wires are commonly used for this purpose as well as for communication with the outside world. However, these wires pose the risk of infection to the patient. Another common method of powering is to utilize batteries in the implant. Nevertheless, this method is not desirable as the batteries have to be replaced at the end of their lifetime with a surgical procedure. This thesis presents the development of a remotely powered wireless cortical neural interface system for brain-machine interface applications. In the scope of this work, firstly, the requirements and specifications of the system are analyzed to examine the limits of operation. In addition, the thermal impact of cortical implant operation in the head is investigated to determine the maximum allowable power consumption in the implant. In order to supply power to the active components in the cortical implant, a closed-loop inductive remote powering link operating from a single external battery is implemented. The closed-loop operation enables adaptive delivery of power depending on the implant activity. For improving the power efficiency of the link, a discrete optimization algorithm is developed to design the geometry of the power transmission coils. In addition, application specific integrated circuits are designed to enhance the overall performance of the system and to decrease the footprint of the implant electronics. Moreover, wireless data communication for cortical implants is discussed and a solution for coexistence of the power and data links is presented. For implanting the cortical recording device into the body, a two-body packaging topology is proposed to position the implant inside the cranial bone. With this topology, the performance of the cortical neural interface is significantly improved. The fabricated cortical implants with the two-body package are characterized in air and in vitro. The power transfer efficiency of the closed-loop remote powering link operating from a single supply is measured to be 10.6% in vitro for 10 mW power delivered to the implant load. Finally, the operation of the implant in vitro is validated for over five weeks

A Closed-Loop Remote Powering Link for Wireless Cortical Implants

This paper presents a closed-loop remote powering link for wireless cortical implants. The link operates from a single power supply at the external reader and delivers power to the implant adaptively under changing load conditions. A feedback information is sent from the implant to the external reader about the power consumption in the implant and the external reader adapts the amount of transmitted power depending on this feedback. In addition, an in vitro measurement setup is fabricated in order to characterize the performance of the wireless energy transfer when the implant is immersed into saline solution. The implant is packaged by using biocompatible materials and the operation of the remote powering link is demonstrated in air and in vitro for a wide range of load power delivered from the voltage regulator. The power transfer efficiency of the overall closed-loop remote powering link is measured to be 10.6% in vitro at nominal load power of 10 mW. Finally, the operation of the implant in vitro is demonstrated over a five-week period

Inductive Power Link for a Wireless Cortical Implant With Two-Body Packaging

This paper presents an inductive power link for remote powering of a wireless cortical implant. The link includes a Class-E power amplifier, a gate driver, an inductive link, and an integrated rectifier. The coils of the inductive link are designed and optimized for remote powering from a distance of 10 mm (scalp thickness). The power amplifier is designed in order to allow closed-loop control of the power delivered to the implant, by controlling the supply voltage. Moreover, a gate driver is added to the system to drive the power amplifier and to characterize the gate losses. A new packaging topology is proposed in order to position the implant inside a hole in the cranial bone, without occupying a large area, but still obtaining a short distance between the remote powering coils. The package is fabricated by using biocompatible materials such as PDMS and Parylene-C. The power efficiency of the remote powering link is characterized for a wide range of load power (1-20 mW) delivered from the rectifier and is measured to be 24.6% at nominal load of 10 mW

System for active skull replacement for brain interface and method of using the same

An active skull replacement system including an implant having an area A, an upper surface, and a bottom surface, adapted to be implanted at least in part into a skull of a subject so to substitute a portion of the skull, the bottom surface arranged to face at least in part a cranial cavity, and having a first wireless bidirectional data communication device, a device operably connected to the bottom surface of the implant, the device adapted to at least one of stimulate a physiological response and record a physiological parameter of the subject, and an external reader adapted to be placed on the scalp of the subject and including a second wireless bidirectional data communication device configured to communicate with the first wireless bidirectional data communication device of the implant to operate the device, wherein the external reader and the implant are fixed and aligned among each other through a magnetic device

A low-cost rate-grade nickel microgyroscope

This paper presents a low-cost microgyroscope with a resolution in the rate-grade at atmospheric pressure, which is fabricated using a CMOScompatible nickel electrofonning process. Angular rate resolution of the gyroscope is increased by matching the resonance frequencies of the drive and sense modes close to each other using symmetric suspensions and electrostatic frequency tuning; whereas, undesired mechanical coupling between the two modes during matched mode operation is reduced by the fully decoupled gyro flexures. Reduced mechanical coupling results in a stable zero-rate output bias, i.e., providing excellent bias stability. The fabricated gyroscope has 18 mu m-thick nickel structural layer with 2.5 mu m capacitive gaps providing an aspect ratio above 7, which results in sensor capacitances about 0.5 pF. The resonance frequencies of the fabricated gyroscope are measured to be 4.09 kHz for the drive-mode and 4.33 kHz for the sense-mode, which are then matched by a tuning voltage less than 12 V dc. The gyroscope is hybrid connected to a CMOS capacitive interface circuit, and the hybrid system operation is controlled by external electronics, constructing an angular rate sensor. The gyroscope is oscillated along the drive-mode to vibration amplitude above 10 mu m. The rate sensor demonstrates a noise-equivalent rate of 0.095 (degrees/s)/HZ(1/2) and short-term bias stability better than 0.1 degrees/s. The nominal scale factor of the sensor is 17.7 mV/(degrees/s) in a measurement range of 100 degrees/s, with a full-scale nonlinearity of only 0.12%. The measurement bandwidth of the gyroscope is currently set to 30 Hz, while it can be extended beyond 100 Hz depending on the application requirements. The quality factor of the sense-mode improves by an order of magnitude at vacuum, which yields an estimated noise-equivalent rate better than 0.05 (degrees/s)/HZ1/2 in a narrowed response bandwidth of 10 Hz. (c) 2006 Elsevier B.V. All fights reserved