An overview of the recent wideband transcutaneous wireless communication techniques
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paper_title: An RFID-Based Closed-Loop Wireless Power Transmission System for Biomedical Applications

paper_content:

This brief presents a standalone closed-loop wireless power transmission system that is built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader (TRF7960) operating at 13.56 MHz. It can be used for inductively powering implantable biomedical devices in a closed loop. Any changes in the distance and misalignment between transmitter and receiver coils in near-field wireless power transmission can cause a significant change in the received power, which can cause either a malfunction or excessive heat dissipation. RFID circuits are often used in an open loop. However, their back telemetry capability can be utilized to stabilize the received voltage on the implant. Our measurements showed that the delivered power to the transponder was maintained at 11.2 mW over a range of 0.5 to 2 cm, while the transmitter power consumption changed from 78 mW to 1.1 W. The closed-loop system can also oppose voltage variations as a result of sudden changes in the load current.
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paper_title: Using Pulse Width Modulation for Wireless Transmission of Neural Signals in Multichannel Neural Recording Systems

paper_content:

We have used a well-known technique in wireless communication, pulse width modulation (PWM) of time division multiplexed (TDM) signals, within the architecture of a novel wireless integrated neural recording (WINeR) system. We have evaluated the performance of the PWM-based architecture and indicated its accuracy and potential sources of error through detailed theoretical analysis, simulations, and measurements on a setup consisting of a 15-channel WINeR prototype as the transmitter and two types of receivers; an Agilent 89600 vector signal analyzer and a custom wideband receiver, with 36 and 75 MHz of maximum bandwidth, respectively. Furthermore, we present simulation results from a realistic MATLAB-Simulink model of the entire WINeR system to observe the system behavior in response to changes in various parameters. We have concluded that the 15-ch WINeR prototype, which is fabricated in a 0.5-mum standard CMOS process and consumes 4.5 mW from plusmn1.5 V supplies, can acquire and wirelessly transmit up to 320 k-samples/s to a 75-MHz receiver with 8.4 bits of resolution, which is equivalent to a wireless data rate of ~ 2.56 Mb/s.
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paper_title: Optimization of Data Coils in a Multiband Wireless Link for Neuroprosthetic Implantable Devices

paper_content:

We have presented the design methodology along with detailed simulation and measurement results for optimizing a multiband transcutaneous wireless link for high-performance implantable neuroprosthetic devices. We have utilized three individual carrier signals and coil/antenna pairs for power transmission, forward data transmission from outside into the body, and back telemetry in the opposite direction. Power is transmitted at 13.56 MHz through a pair of printed spiral coils (PSCs) facing each other. Two different designs have been evaluated for forward data coils, both of which help to minimize power carrier interference in the received data carrier. One is a pair of perpendicular coils that are wound across the diameter of the power PSCs. The other design is a pair of planar figure-8 coils that are in the same plane as the power PSCs. We have compared the robustness of each design against horizontal misalignments and rotations in different directions. Simulation and measurements are also conducted on a miniature spiral antenna, designed to operate with impulse-radio ultra-wideband (IR-UWB) circuitry for back telemetry.
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paper_title: Brain–machine interfaces: past, present and future

paper_content:

Since the original demonstration that electrical activity generated by ensembles of cortical neurons can be employed directly to control a robotic manipulator, research on brain–machine interfaces (BMIs) has experienced an impressive growth. Today BMIs designed for both experimental and clinical studies can translate raw neuronal signals into motor commands that reproduce arm reaching and hand grasping movements in artificial actuators. Clearly, these developments hold promise for the restoration of limb mobility in paralyzed subjects. However, as we review here, before this goal can be reached several bottlenecks have to be passed. These include designing a fully implantable biocompatible recording device, further developing real-time computational algorithms, introducing a method for providing the brain with sensory feedback from the actuators, and designing and building artificial prostheses that can be controlled directly by brain-derived signals. By reaching these milestones, future BMIs will be able to drive and control revolutionary prostheses that feel and act like the human arm.
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paper_title: An Inductively Powered Scalable 32-Channel Wireless Neural Recording System-on-a-Chip for Neuroscience Applications

paper_content:

We present an inductively powered 32-channel wireless integrated neural recording (WINeR) system-on-a-chip (SoC) to be ultimately used for one or more small freely behaving animals. The inductive powering is intended to relieve the animals from carrying bulky batteries used in other wireless systems, and enables long recording sessions. The WINeR system uses time-division multiplexing along with a novel power scheduling method that reduces the current in unused low-noise amplifiers (LNAs) to cut the total SoC power consumption. In addition, an on-chip high-efficiency active rectifier with optimized coils help improve the overall system power efficiency, which is controlled in a closed loop to supply stable power to the WINeR regardless of the coil displacements. The WINeR SoC has been implemented in a 0.5-μ m standard complementary metal-oxide semiconductor process, measuring 4.9×3.3 mm2 and consuming 5.85 mW at ±1.5 V when 12 out of 32 LNAs are active at any time by power scheduling. Measured input-referred noise for the entire system, including the receiver located at 1.2 m, is 4.95 μVrms in the 1 Hz~10 kHz range when the system is inductively powered with 7-cm separation between aligned coils.
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paper_title: Design and Optimization of Printed Spiral Coils for Efficient Transcutaneous Inductive Power Transmission

paper_content:

The next generation of implantable high-power neuroprosthetic devices such as visual prostheses and brain computer interfaces are going to be powered by transcutaneous inductive power links formed between a pair of printed spiral coils (PSC) that are batch-fabricated using micromachining technology. Optimizing the power efficiency of the wireless link is imperative to minimize the size of the external energy source, heating dissipation in the tissue, and interference with other devices. Previous design methodologies for coils made of 1-D filaments are not comprehensive and accurate enough to consider all geometrical aspects of PSCs with planar 3-D conductors as well as design constraints imposed by implantable device application and fabrication technology. We have outlined the theoretical foundation of optimal power transmission efficiency in an inductive link, and combined it with semi-empirical models to predict parasitic components in PSCs. We have used this foundation to devise an iterative PSC design methodology that starts with a set of realistic design constraints and ends with the optimal PSC pair geometries. We have executed this procedure on two design examples at 1 and 5 MHz achieving power transmission efficiencies of 41.2% and 85.8%, respectively, at 10-mm spacing. All results are verified with simulations using a commercial field solver (HFSS) as well as measurements using PSCs fabricated on printed circuit boards.
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paper_title: Toward the development of a cortically based visual neuroprosthesis

paper_content:

Motivated by the success of cochlear implants for deaf patients, we are now facing the goal of creating a visual neuroprosthesis designed to interface with the occipital cortex as a means through which a limited but useful sense of vision could be restored in profoundly blind patients. We review the most important challenges regarding this neuroprosthetic approach and emphasize the need for basic human psychophysical research on the best way of presenting complex stimulating patterns through multiple microelectrodes. Continued research will hopefully lead to the development of and design specifications for the first generation of a cortically based visual prosthesis system.
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paper_title: An advanced multiple channel cochlear implant

paper_content:

In the hearing prosthesis, stimulation is presented through an array of 20 electrodes located in the scala tympani. Any two electrodes can be configured as a bipolar pair to conduct a symmetrical, biphasic, constant-current pulsatile stimulus. Up to three stimuli can be presented in rapid succession or effectively simultaneously. For simultaneous stimulation, a novel time-division current multiplexing technique has been developed to obviate electrode interactions that may compromise safety. The stimuli are independently controllable in current amplitude, duration, and onset time. Groups of three stimuli can be generated at a rate of typically 500 Hz. Stimulus control data and power are conveyed to the implant through a single transcutaneous inductive link. The device incorporates a telemetry system that enables electrode voltage waveforms to be monitored externally in real time. The electronics of the implant are contained almost entirely on a custom designed integrated circuit. Preliminary results obtained with the first patient to receive the advanced implant are included. >
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paper_title: Design and Optimization of Printed Spiral Coils for Efficient Transcutaneous Inductive Power Transmission

paper_content:

The next generation of implantable high-power neuroprosthetic devices such as visual prostheses and brain computer interfaces are going to be powered by transcutaneous inductive power links formed between a pair of printed spiral coils (PSC) that are batch-fabricated using micromachining technology. Optimizing the power efficiency of the wireless link is imperative to minimize the size of the external energy source, heating dissipation in the tissue, and interference with other devices. Previous design methodologies for coils made of 1-D filaments are not comprehensive and accurate enough to consider all geometrical aspects of PSCs with planar 3-D conductors as well as design constraints imposed by implantable device application and fabrication technology. We have outlined the theoretical foundation of optimal power transmission efficiency in an inductive link, and combined it with semi-empirical models to predict parasitic components in PSCs. We have used this foundation to devise an iterative PSC design methodology that starts with a set of realistic design constraints and ends with the optimal PSC pair geometries. We have executed this procedure on two design examples at 1 and 5 MHz achieving power transmission efficiencies of 41.2% and 85.8%, respectively, at 10-mm spacing. All results are verified with simulations using a commercial field solver (HFSS) as well as measurements using PSCs fabricated on printed circuit boards.
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paper_title: An Overview of Near Field UHF RFID

paper_content:

In this paper, an overview of near field UHF RFID is presented. This technology recently received attention because of its possible use for item-level tagging where LF/HF RFID has traditionally been used. We review the relevant literature, discuss basic theory of near and far field antenna coupling in application to RFID, and present some experimental measurements.
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paper_title: An Inductively Powered Scalable 32-Channel Wireless Neural Recording System-on-a-Chip for Neuroscience Applications

paper_content:

We present an inductively powered 32-channel wireless integrated neural recording (WINeR) system-on-a-chip (SoC) to be ultimately used for one or more small freely behaving animals. The inductive powering is intended to relieve the animals from carrying bulky batteries used in other wireless systems, and enables long recording sessions. The WINeR system uses time-division multiplexing along with a novel power scheduling method that reduces the current in unused low-noise amplifiers (LNAs) to cut the total SoC power consumption. In addition, an on-chip high-efficiency active rectifier with optimized coils help improve the overall system power efficiency, which is controlled in a closed loop to supply stable power to the WINeR regardless of the coil displacements. The WINeR SoC has been implemented in a 0.5-μ m standard complementary metal-oxide semiconductor process, measuring 4.9×3.3 mm2 and consuming 5.85 mW at ±1.5 V when 12 out of 32 LNAs are active at any time by power scheduling. Measured input-referred noise for the entire system, including the receiver located at 1.2 m, is 4.95 μVrms in the 1 Hz~10 kHz range when the system is inductively powered with 7-cm separation between aligned coils.
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paper_title: An ultra low power, high performance Medical Implant Communication System (MICS) transceiver for implantable devices

paper_content:

A 402-405 MHz MICS band transceiver has been developed for implantable medical applications. The transceiver offers exceptionally low power consumption whilst providing a high data rate. The circuit features a unique ultra low power wakeup system enabling an average sleep current of less than 250 nA. The transmit and receive current is less than 5 mA when operating at a data rate of up to 800 kbps. System integration is high and only 3 external components (crystal and 2 decoupling capacitors) and a matching network are required. The transceiver can also operate in the 433 MHz ISM band. The key system design features and performance of this transceiver are presented in this paper.
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paper_title: A wireless neural/EMG telemetry system for freely moving insects

paper_content:

We have developed a miniature telemetry system that captures neural, EMG, and acceleration signals from a freely moving insect and transmits the data wirelessly to a remote digital receiver. The system is based on a custom low-power integrated circuit that amplifies and digitizes four biopotential signals as well as three acceleration signals from an off-chip MEMS accelerometer, and transmits this information over a wireless 920-MHz telemetry link. The unit weighs 0.79 g and runs for two hours on two small batteries. We have used this system to monitor neural and EMG signals in jumping and flying locusts.
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paper_title: Modeling and Optimization of Printed Spiral Coils in Air, Saline, and Muscle Tissue Environments

paper_content:

Printed spiral coils (PSCs) are viable candidates for near-field wireless power transmission to the next generation of high-performance neuroprosthetic devices with extreme size constraints, which will target intraocular and intracranial spaces. Optimizing the PSC geometries to maximize the power transfer efficiency of the wireless link is imperative to reduce the size of the external energy source, heating of the tissue, and interference with other devices. Implantable devices need to be hermetically sealed in biocompatible materials and placed in a conductive environment with high permittivity (tissue), which can affect the PSC characteristics. We have constructed a detailed model that includes the effects of the surrounding environment on the PSC parasitic components and eventually on the power transfer efficiency. We have combined this model with an iterative design method that starts with a set of realistic design constraints and ends with the optimal PSC geometries. We applied our design methodology to optimize the wireless link of a 1-cm 2 implantable device example, operating at 13.56 MHz. Measurement results showed that optimized PSC pairs, coated with 0.3 mm of silicone, achieved 72.2%, 51.8%, and 30.8% efficiencies at a face-to-face relative distance of 10 mm in air, saline, and muscle, respectively. The PSC, which was optimized for air, could only bear 40.8% and 21.8% efficiencies in saline and muscle, respectively, showing that by including the PSC tissue environment in the design process the result can be more than a 9% improvement in the power transfer efficiency.
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paper_title: Optimization of Data Coils in a Multiband Wireless Link for Neuroprosthetic Implantable Devices

paper_content:

We have presented the design methodology along with detailed simulation and measurement results for optimizing a multiband transcutaneous wireless link for high-performance implantable neuroprosthetic devices. We have utilized three individual carrier signals and coil/antenna pairs for power transmission, forward data transmission from outside into the body, and back telemetry in the opposite direction. Power is transmitted at 13.56 MHz through a pair of printed spiral coils (PSCs) facing each other. Two different designs have been evaluated for forward data coils, both of which help to minimize power carrier interference in the received data carrier. One is a pair of perpendicular coils that are wound across the diameter of the power PSCs. The other design is a pair of planar figure-8 coils that are in the same plane as the power PSCs. We have compared the robustness of each design against horizontal misalignments and rotations in different directions. Simulation and measurements are also conducted on a miniature spiral antenna, designed to operate with impulse-radio ultra-wideband (IR-UWB) circuitry for back telemetry.
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paper_title: A Non-Coherent DPSK Data Receiver With Interference Cancellation for Dual-Band Transcutaneous Telemetries

paper_content:

A dual-band telemetry, which has different carrier frequencies for power and data signals, is used to maximize both power transfer efficiency and data rate for transcutaneous implants. However, in such a system, the power signal interferes with the data transmission due to the multiple magnetic couplings paths within the inductive coils. Since the power level of the transmitted power signal is significantly larger than that of the data signal, it usually requires a high-order filter to suppress the interference. This paper presents a non-coherent DPSK receiver without a high-order filter that is robust to the interference caused by the power carrier signal. The proposed scheme uses differential demodulation in the analog domain to cancel the interference signal for a dual-band configuration. The data demodulation also uses subsampling to avoid carrier synchronization circuits such as PLLs. The experimental results show that the demodulator can recover 1 and 2 Mb/s data rates at a 20 MHz carrier frequency, and it is able to cancel an interference signal that is 12 dB larger than the data signal without using complex filters. The demodulator is fabricated in a 0.35 mum CMOS process, with a power consumption of 6.2 mW and an active die area of 2.6times1.7mm2.
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paper_title: Design and Optimization of Printed Spiral Coils for Efficient Transcutaneous Inductive Power Transmission

paper_content:

The next generation of implantable high-power neuroprosthetic devices such as visual prostheses and brain computer interfaces are going to be powered by transcutaneous inductive power links formed between a pair of printed spiral coils (PSC) that are batch-fabricated using micromachining technology. Optimizing the power efficiency of the wireless link is imperative to minimize the size of the external energy source, heating dissipation in the tissue, and interference with other devices. Previous design methodologies for coils made of 1-D filaments are not comprehensive and accurate enough to consider all geometrical aspects of PSCs with planar 3-D conductors as well as design constraints imposed by implantable device application and fabrication technology. We have outlined the theoretical foundation of optimal power transmission efficiency in an inductive link, and combined it with semi-empirical models to predict parasitic components in PSCs. We have used this foundation to devise an iterative PSC design methodology that starts with a set of realistic design constraints and ends with the optimal PSC pair geometries. We have executed this procedure on two design examples at 1 and 5 MHz achieving power transmission efficiencies of 41.2% and 85.8%, respectively, at 10-mm spacing. All results are verified with simulations using a commercial field solver (HFSS) as well as measurements using PSCs fabricated on printed circuit boards.
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paper_title: A wideband power-efficient inductive wireless link for implantable microelectronic devices using multiple carriers

paper_content:

This paper presents a novel inductive link for wireless transmission of power and data to biomedical implantable microelectronic devices using multiple carrier frequencies. Achieving higher data bandwidth without compromising the power efficiency is the driving force to use two separate carriers. Two separate pairs of coils have been utilized for inductive power and forward data transmission. One major challenge, however, is to minimize the interference among these carriers especially on the implantable side, where size and power are highly limited. Planar power coils with spiral shape are optimized in geometry to provide maximum coupling coefficient, k. The data coils are designed rectangular in shape and wound across the power coils diameter to be oriented perpendicular to the power coil planes. The goal is to maximize data coils direct coupling, while minimize their cross-coupling with the power coils. The effects of coils geometry, relative distance, and misalignments on the coupling coefficients have been modeled and experimentally measured.
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paper_title: High-Speed OQPSK and Efficient Power Transfer Through Inductive Link for Biomedical Implants

paper_content:

Biomedical implants require wireless power and bidirectional data transfer. We pursue our previous work on a novel topology for a multiple carrier inductive link by presenting the fabricated coils. We show that the coplanar geometry approach is better suited for displacement tolerance. We provide a theoretical analysis of the efficiency of power transfer and phase-shift-keying communications through an inductive link. An efficiency of up to 61% has been achieved experimentally for power transfer and a data rate of 4.16 Mb/s with a bit-error rate of less than 2 × 10-6 has been obtained with our fabricated offset quadrature phase-shift keying modules due to the inductive link optimization presented in this paper.
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paper_title: A Wireless Implantable Multichannel Microstimulating System-on-a-Chip With Modular Architecture

paper_content:

A 64-site wireless current microstimulator chip (Interestim-2B) and a prototype implant based on the same chip have been developed for neural prosthetic applications. Modular standalone architecture allows up to 32 chips to be individually addressed and operated in parallel to drive up to 2048 stimulating sites. The only off-chip components are a receiver inductive-capac- itive (LC) tank, a capacitive low-pass filter for ripple rejection, and arrays of microelectrodes for interfacing with the neural tissue. The implant receives inductive power up to 50 mW and data at 2.5 Mb/s from a frequency shift keyed (FSK) 5/10 MHZ carrier to generate up to 65 800 stimulus pulses/s. Each Interestim-2B chip contains 16 current drivers with 270 muA full-scale current, 5-bit (32-steps) digital-to-analog converter (DAC) resolution, 100 MOmega output impedance, and a voltage compliance that extends within 150 and 250 mV of the 5 V supply and ground rails, respectively. It can generate any arbitrary current waveform and supports a variety of monopolar and bipolar stimulation protocols. A common analog line provides access to each site potential, and exhausts residual stimulus charges for charge balancing. The chip has site potential measurement and in situ site impedance measurement capabilities, which help its users indicate defective sites or characteristic shifts in chronic stimulations. Interestim-2B chip is fabricated in the AMI 1.5 mum standard complementary metal-oxide-semiconductor (CMOS) process and measures 4.6 x 4.6 x 0.5 mm. The prototype implant size including test connectors is 19 X 14 x 6 mm, which can be shrunk down to <0.5 CC. This paper also summarizes some of the in vitro and in vivo experiments performed using the Interestim-2B prototype implant.
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paper_title: A 10.2 Mbps Pulse Harmonic Modulation Based Transceiver for Implantable Medical Devices

paper_content:

A low power wireless transceiver has been presented for near-field data transmission across inductive telemetry links, which operates based on pulse harmonic modulation (PHM). This PHM transceiver uses on-off keying (OOK) of a pattern of pulses to suppress inter-symbol interference (ISI), and its characteristics are suitable for low-power high-bandwidth telemetry in implantable neuroprosthetic devices. To transmit each bit across a pair of high-Q LC-tank circuits, the PHM transmitter generates a string of narrow pulses with specific amplitudes and timing. Each pulse generates a decaying oscillation at the harmonic frequency that the receiver LC-tank is tuned at, which is then superimposed with other oscillations across the receiver at the same frequency, to minimize the ISI. This allows for reaching high data rates without reducing the inductive link quality factor (to extend its bandwidth), which significantly improves the range and selectivity of the link. The PHM receiver architecture is based on non-coherent energy detection with programmable bandwidth and adjustable gain. The PHM transceiver was fabricated in a 0.5- μm standard CMOS process, occupying 1.8 mm2. The transceiver achieved a measured 10.2 Mbps data rate with a bit error rate (BER) of 6.3×10-8 at 1 cm distance using planar implant sized (1 cm2) figure-8 coils. The PHM transmitter power consumption was 345 pJ/bit and 8.85 pJ/bit at 1 cm and zero link distances, respectively. The receiver dissipates 3 mW at 3.3 V supply voltage.
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paper_title: Wideband Near-Field Data Transmission Using Pulse Harmonic Modulation

paper_content:

This paper introduces a new modulation technique, called pulse harmonic modulation (PHM), for wideband, low power data transmission across inductive telemetry links that operate in the near-field domain. The use of sharp and narrow pulses, similar to impulse-radio ultrawideband (IR-UWB) in the far-field domain, leads to significant reduction in the transmitter power consumption. However unlike IR-UWB, where all pulses are the same, in PHM each bit consists of a pattern of pulses with specific time delays and amplitudes, which minimize the intersymbol interference (ISI) across the receiver coil. This helps achieve a high data rate without reducing the inductive link quality factor and selectivity, which are necessary to block interferers. The received signal consists of an oscillation pattern that is amplitude modulated by the amplitude and timing of the successively transmitted pulses to facilitate data demodulation with low bit-error rate (BER). The main application of the PHM is expected to be in the neuroprostheses, such as brain-computer interfaces (BCIs) or cochlear/retinal implants, which need to transfer large volumes of data across the skin. It may also be used in short-range proximity-based digital communications with high-throughput wireless devices. This paper describes the PHM theoretical foundation and demonstrates its operation with a proof-of-concept prototype setup, which achieves a data rate of 5.2 Mbps at 1 cm coil separation with a BER of 10- 6 .
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paper_title: A wideband frequency-shift keying wireless link for inductively powered biomedical implants

paper_content:

A high data-rate frequency-shift keying (FSK) modulation protocol, a wideband inductive link, and three demodulator circuits have been developed with a data-rate-to-carrier-frequency ratio of up to 67%. The primary application of this novel FSK modulation/demodulation technique is to send data to inductively powered wireless biomedical implants at data rates in excess of 1 Mbps, using comparable carrier frequencies. This method can also be used in other applications such as radio-frequency identification tags and contactless smartcards by adding a back telemetry link. The inductive link utilizes a series-parallel inductive-capacitance tank combination on the transmitter side to provide more than 5 MHz of bandwidth. The demodulator circuits detect data bits by directly measuring the duration of each received FSK carrier cycle, as well as derive a constant frequency clock, which is used to sample the data bits. One of the demodulator circuits, digital FSK, occupies 0.29 mm/sup 2/ in the AMI 1.5-/spl mu/m, 2M/2P, standard CMOS process, and consumes 0.38 mW at 5 V. This circuit is simulated up to 4 Mbps, and experimentally tested up to 2.5 Mbps with a bit error rate of 10/sup -5/, while receiving a 5/10-MHz FSK carrier signal. It is also used in a wireless implantable neural microstimulation system.
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paper_title: A Tri-State FSK Demodulator for Asynchronous Timing of High-Rate Stimulation Pulses in Wireless Implantable Microstimulators

paper_content:

A tri-state FSK modulation protocol and demodulator circuit have been developed and explained in this paper for wireless data rates as high as the carrier frequency. This method is used for asynchronous timing of high-rate stimulation pulses in wireless implantable microstimulators to improve the timing resolution of the stimulation pulses from one data-frame period to only one carrier cycle period. The demodulator circuit is used in a 16-site wireless active stimulating microprobe fabricated in the University of Michigan 3-mum, 1-metal, 2-poly, N-epi, BiCMOS process, occupying 1.17 mm2 of the probe active area. The FSK demodulator circuit is simulated up to 2.5 Mega bits per second (b/s) and tested up to 300 kb/s
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paper_title: IMES - implantable myoElectric sensor system: Designing standardized ASICs

paper_content:

As a component of the RP2009 project, the IMES system has emerged as a strong candidate for extracting naturally-occurring control signals to be used for providing functional control of an upper body artificial limb. In earlier publications, we described various elements of this system as they were being researched and developed. Presently, the system has matured to a level for which it is now appropriate to consider application-specific-integrated circuits (ASIC) that are of a standardized form, and are suitable for clinical deployment of the IMES system. Here we describe one of our emerging ASIC designs that addresses the design challenges of the extracoporal transmitter controller. Although this ASIC is used in the IMES system, it may also be used for any command protocol that requires FSK modulation of a Class E converter.
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paper_title: Power-Efficient Impedance-Modulation Wireless Data Links for Biomedical Implants

paper_content:

We analyze the performance of wireless data telemetry links for implanted biomedical systems. An experimental realization of a bidirectional half-duplex link that uses near-field inductive coupling between the implanted system and an external transceiver is described. Our system minimizes power consumption in the implanted system by using impedance modulation to transmit high-bandwidth information in the uplink direction, i.e., from the implanted to the external system. We measured a data rate of 2.8 Mbps at a bit error rate (BER) of <10-6 (we could not measure error rates below 10-6 ) and a data rate of 4.0 Mbps at a BER of 10-3. Experimental results also demonstrate data transfer rates up to 300 kbps in the opposite, i.e., downlink direction. We also perform a theoretical analysis of the bit error rate performance. An important effect regarding the asymmetry of rising and falling edges that is inherent to impedance modulation is predicted by theory and confirmed by experiment. The link dissipates 2.5 mW in the external system and only 100 muW in the implanted system, making it among the most power-efficient inductive data links reported. Our link is compatible with FCC regulations on radiated emissions.
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paper_title: A 10.8 mW Body Channel Communication/MICS Dual-Band Transceiver for a Unified Body Sensor Network Controller

paper_content:

With the increasing number of portable and implantable personal health care devices, there is a strong demand to control their communication in a single wireless network. Recently, the IEEE 802.15 WBAN task group has discussed the combining of wearable and implantable body sensor networks (BSNs) [1], but no real chip implementation has been reported. In this paper, the implementation of a unified BSN as shown in Fig. 24.9.1 is described.. The unified BSN combines low-power body-channel communication (BCC) [2] and versatile medical implant communication service (MICS) [3] using a network controller located on the human body. This unified BSN has 2 main advantages over the conventional BSNs. First, the MICS band antenna shared with the BCC electrode can be attached directly to human skin to shorten the communication distances among the controller and implanted radios, relaxing their sensitivity and selectivity requirements. Second, due to low path loss of the human body channel, low-power communication is possible among the wearable devices [4]. In addition, the on-body sensors do not need external antennas because the bio-signal sensing electrode functions as the interface for data transmission.
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paper_title: Optimization of Data Coils in a Multiband Wireless Link for Neuroprosthetic Implantable Devices

paper_content:

We have presented the design methodology along with detailed simulation and measurement results for optimizing a multiband transcutaneous wireless link for high-performance implantable neuroprosthetic devices. We have utilized three individual carrier signals and coil/antenna pairs for power transmission, forward data transmission from outside into the body, and back telemetry in the opposite direction. Power is transmitted at 13.56 MHz through a pair of printed spiral coils (PSCs) facing each other. Two different designs have been evaluated for forward data coils, both of which help to minimize power carrier interference in the received data carrier. One is a pair of perpendicular coils that are wound across the diameter of the power PSCs. The other design is a pair of planar figure-8 coils that are in the same plane as the power PSCs. We have compared the robustness of each design against horizontal misalignments and rotations in different directions. Simulation and measurements are also conducted on a miniature spiral antenna, designed to operate with impulse-radio ultra-wideband (IR-UWB) circuitry for back telemetry.
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paper_title: A wideband power-efficient inductive wireless link for implantable microelectronic devices using multiple carriers

paper_content:

This paper presents a novel inductive link for wireless transmission of power and data to biomedical implantable microelectronic devices using multiple carrier frequencies. Achieving higher data bandwidth without compromising the power efficiency is the driving force to use two separate carriers. Two separate pairs of coils have been utilized for inductive power and forward data transmission. One major challenge, however, is to minimize the interference among these carriers especially on the implantable side, where size and power are highly limited. Planar power coils with spiral shape are optimized in geometry to provide maximum coupling coefficient, k. The data coils are designed rectangular in shape and wound across the power coils diameter to be oriented perpendicular to the power coil planes. The goal is to maximize data coils direct coupling, while minimize their cross-coupling with the power coils. The effects of coils geometry, relative distance, and misalignments on the coupling coefficients have been modeled and experimentally measured.
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paper_title: An AC-powered optical receiver consuming 270μW for transcutaneous 2Mb/s data transfer

paper_content:

Improving communication with implantable systems remains an important topic of research due to the limitations in power dissipation and the simultaneous need for high data rates. Neural recorders generate well above 10Mb/s data [1], which needs to be transmitted out-of-body. Multichannel stimulators, such as epiretinal implants, need control data in the range of several Mb/s for the into-body link [2]. Up to now, RF has been the dominant form of transcutaneous communication. One major issue is the crosstalk between the RF power link and the data signal. Therefore, dual-band telemetry is common in order to spectrally separate the data and power transfer. The standards reach from UWB transmitters [1], MICS band [3], to customized [2] RF receivers, often using sophisticated digital encoding. Also, orthogonal alignment has been used for the data and power coils to suppress crosstalk. Such RF communication needs a 2nd pair of coils, and the state-of-the-art power consumption ranges from 1.5 to 3nJ/b at rates of 120kb/s to 2.5Mb/s [3].
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paper_title: Wideband Near-Field Data Transmission Using Pulse Harmonic Modulation

paper_content:

This paper introduces a new modulation technique, called pulse harmonic modulation (PHM), for wideband, low power data transmission across inductive telemetry links that operate in the near-field domain. The use of sharp and narrow pulses, similar to impulse-radio ultrawideband (IR-UWB) in the far-field domain, leads to significant reduction in the transmitter power consumption. However unlike IR-UWB, where all pulses are the same, in PHM each bit consists of a pattern of pulses with specific time delays and amplitudes, which minimize the intersymbol interference (ISI) across the receiver coil. This helps achieve a high data rate without reducing the inductive link quality factor and selectivity, which are necessary to block interferers. The received signal consists of an oscillation pattern that is amplitude modulated by the amplitude and timing of the successively transmitted pulses to facilitate data demodulation with low bit-error rate (BER). The main application of the PHM is expected to be in the neuroprostheses, such as brain-computer interfaces (BCIs) or cochlear/retinal implants, which need to transfer large volumes of data across the skin. It may also be used in short-range proximity-based digital communications with high-throughput wireless devices. This paper describes the PHM theoretical foundation and demonstrates its operation with a proof-of-concept prototype setup, which achieves a data rate of 5.2 Mbps at 1 cm coil separation with a BER of 10- 6 .
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paper_title: Listening to Brain Microcircuits for Interfacing With External World—Progress in Wireless Implantable Microelectronic Neuroengineering Devices

paper_content:

Acquiring neural signals at high spatial and temporal resolution directly from brain microcircuits and decoding their activity to interpret commands and/or prior planning activity, such as motion of an arm or a leg, is a prime goal of modern neurotechnology. Its practical aims include assistive devices for subjects whose normal neural information pathways are not functioning due to physical damage or disease. On the fundamental side, researchers are striving to decipher the code of multiple neural microcircuits which collectively make up nature's amazing computing machine, the brain. By implanting biocompatible neural sensor probes directly into the brain, in the form of microelectrode arrays, it is now possible to extract information from interacting populations of neural cells with spatial and temporal resolution at the single cell level. With parallel advances in application of statistical and mathematical techniques tools for deciphering the neural code, extracted populations or correlated neurons, significant understanding has been achieved of those brain commands that control, e.g., the motion of an arm in a primate (monkey or a human subject). These developments are accelerating the work on neural prosthetics where brain derived signals may be employed to bypass, e.g., an injured spinal cord. One key element in achieving the goals for practical and versatile neural prostheses is the development of fully implantable wireless microelectronic ?brain-interfaces? within the body, a point of special emphasis of this paper.
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paper_title: An advanced multiple channel cochlear implant

paper_content:

In the hearing prosthesis, stimulation is presented through an array of 20 electrodes located in the scala tympani. Any two electrodes can be configured as a bipolar pair to conduct a symmetrical, biphasic, constant-current pulsatile stimulus. Up to three stimuli can be presented in rapid succession or effectively simultaneously. For simultaneous stimulation, a novel time-division current multiplexing technique has been developed to obviate electrode interactions that may compromise safety. The stimuli are independently controllable in current amplitude, duration, and onset time. Groups of three stimuli can be generated at a rate of typically 500 Hz. Stimulus control data and power are conveyed to the implant through a single transcutaneous inductive link. The device incorporates a telemetry system that enables electrode voltage waveforms to be monitored externally in real time. The electronics of the implant are contained almost entirely on a custom designed integrated circuit. Preliminary results obtained with the first patient to receive the advanced implant are included. >
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paper_title: Hybrid RF/IR transcutaneous telemetry for power and high-bandwidth data

paper_content:

As neuroprosthetic control systems continue to advance and increase in channel density, there will be a constant need to deliver data at higher bandwidths in and out of the body. Currently, RF telemetry and inductive coupling are the most commonly used methods for transmitting power and electronic data between implants and external systems, and state of the art systems can deliver data rates up to hundreds of kilobits per second. However, it is difficult to operate implanted medical RF links at higher data rates due to electromagnetic compatibility (EMC) constraints. In this study, we investigate the potential for hybrid telemetry systems that use constant-frequency RF inductive links for power and transcutaneous infrared (IR) signals for data. We show that with commercially available infrared communication components, data rates of up to 40 Mbits per second can be transmitted out across 5 mm of skin with an internal device power dissipation under 100 mW.
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Title: An Overview of the Recent Wideband Transcutaneous Wireless Communication Techniques

Section 1: Introduction
Description 1: Outline the challenges and importance of transcutaneous data telemetry in implantable medical devices, highlighting the need for wireless communication techniques for patient comfort and safety.

Section 2: Reactive vs. Radiative
Description 2: Explain the division of the area around a radio frequency transmitter into regions, and discuss the implications for transcutaneous communications, including the use of Industrial-Scientific-Medical (ISM) bands and limitations of current data rates.

Section 3: Single Carrier vs. Multi-Carrier
Description 3: Discuss the power consumption issues in neuroprosthetic devices, advantages and disadvantages of using single carrier signals for power and data transmission, and the challenges of implementing multiple carrier signals within limited space.

Section 4: Carrier Based vs. Pulse Based
Description 4: Review various modulation techniques for transcutaneous data telemetry, with a focus on phase-coherent Frequency Shift Keying (pcFSK) and Pulse Harmonic Modulation (PHM) for improving data rates and minimizing interference.

Section 5: Electromagnetic, Optical, and Body Channel
Description 5: Explore alternative methods to RF electromagnetic fields for transcutaneous communication, including optical links and using the human body as the channel, along with their respective advantages and limitations.

Section 6: Conclusion
Description 6: Summarize the challenges and proposed solutions for designing wideband transcutaneous links, emphasizing the importance of decoupling data carrier from power and optimizing coil and antenna designs.