Faycal Mounaim

Integrated High-Voltage Inductive Power and Data-Recovery Front End Dedicated to Implantable Devices

In near-field electromagnetic links, the inductive voltage is usually much larger than the compliance of low-voltage integrated-circuit (IC) technologies used for the implementation of implantable devices. Thus most integrated power-recovery approaches limit the induced signal to low voltages with inefficient shunt regulation or voltage clipping. In this paper, we propose using high-voltage (HV) complementary metal-oxide semiconductor technology to fully integrate the inductive power and data-recovery front end while adopting a step-down approach where the inductive voltage is left free up to 20 or 50 V. The advantage is that excessive inductive power will translate to an additional charge that can be stored in a capacitor, instead of shunting to ground excessive current with voltage limiters. We report the design of two consecutive HV custom ICs-IC1 and IC2-fabricated in DALSA semiconductor C08G and C08E technologies, respectively, with a total silicon area (including pads) of 4 and 9 mm2, respectively. Both ICs include HV rectification and regulation; however, IC2 includes two enhanced rectifier designs, a voltage-doubler, and a bridge rectifier, as well as data recovery. Postlayout simulations show that both IC2 rectifiers achieve more than 90% power efficiency at a 1-mA load and provide enough room for 12-V regulation at a 3-mA load and a maximum-available inductive power of 50 mW only. Successful measurement results show that HV regulators provide a stable 3.3- to 12-V supply from an unregulated input up to 50 or 20 V for IC1 and IC2, respectively, with performance that matches simulation results.

Inductive Power Transfer System With Self-Calibrated Primary Resonant Frequency

Inductive power transfer (IPT) is a commonly employed technique for wirelessly supplying power to implantable medical devices. A major limit of this approach is the sensitivity of the inductive link to coupling factor variations between transmitting and receiving coils. We propose in this paper a new method for compensating these variations and improving the inductive link efficiency. The proposed technique is based on a mechatronic module that dynamically tunes the primary resonant capacitor value in order to maintain the resonance state of the IPT system. The module is able to maintain resonance state for apparent primary inductance range at least from 0.5 to 5 μH using a high capacitance resolution of 0.032 pF. Experimentations conducted on a 13.56MHz IPT system showed a 65% higher power transfer compared to a traditional IPT system.

Electrode–tissues interface: modeling and experimental validation

The electrode-tissues interface (ETI) is one of the key issues in implantable devices such as stimulators and sensors. Once the stimulator is implanted, safety and reliability become more and more critical. In this case, modeling and monitoring of the ETI are required. We propose an empirical model for the ETI and a dedicated integrated circuit to measure its corresponding complex impedance. These measurements in the frequency range of 1 Hz to 100 kHz were achieved in acute dog experiments. The model demonstrates a closer fitting with experimental measurements. In addition, a custom monitoring device based on a stimuli current generator has been completed to evaluate the phase shift and voltage across the electrodes and to transmit wirelessly the values to an external controller. This integrated circuit has been fabricated in a CMOS 0.18 microm process, which consumes 4 mW only during measurements and occupies an area of 1 mm(2).

Bidirectional high data rate transmission interface for inductively powered devices

High data transfer rates in the order of 1 Mbit/s are now in demand for some inductively powered devices, but communication needs to be made without compromising power transfer and its efficiency. This paper compares different modulation schemes and proposes an interface to satisfy demanding bidirectional transmission needs. New demodulation approaches are used for phase and amplitude modulation and an adapted configurable protocol is presented. A complete integrated system is under design with a submicron technology. A transfer rate of 1.13 Mbit/s has been obtained with a discrete component prototype for amplitude demodulation.

Toward A Fully Integrated Neurostimulator With Inductive Power Recovery Front-End

In order to investigate new neurostimulation strategies for micturition recovery in spinal cord injured patients, custom implantable stimulators are required to carry-on chronic animal experiments. However, higher integration of the neurostimulator becomes increasingly necessary for miniaturization purposes, power consumption reduction, and for increasing the number of stimulation channels. As a first step towards total integration, we present in this paper the design of a highly-integrated neurostimulator that can be assembled on a 21-mm diameter printed circuit board. The prototype is based on three custom integrated circuits fabricated in High-Voltage (HV) CMOS technology, and a low-power small-scale commercially available FPGA. Using a step-down approach where the inductive voltage is left free up to 20 V, the inductive power and data recovery front-end is fully integrated. In particular, the front-end includes a bridge rectifier, a 20-V voltage limiter, an adjustable series regulator (5 to 12 V), a switched-capacitor step-down DC/DC converter (1:3, 1:2, or 2:3 ratio), as well as data recovery. Measurements show that the DC/DC converter achieves more than 86% power efficiency while providing around 3.9-V from a 12-V input at 1-mA load, 1:3 conversion ratio, and 50-kHz switching frequency. With such efficiency, the proposed step-down inductive power recovery topology is more advantageous than its conventional step-up counterpart. Experimental results confirm good overall functionality of the system.

Miniature Implantable System Dedicated to Bi-Channel Selective Neurostimulation

This paper concerns the design and implementation of a bi-channel selective neurostimulator (BSN). It is dedicated to demonstrate the efficiency of bilateral sacral roots stimulation during chronic experiments in small animals (rats). The complete BSN implant has been highly miniaturized. It is powered and controlled by an inductive RF link and includes two channels. Even though they are meant for simultaneous operation, the channels outputs are synchronized to avoid drawing high stimulation currents at the same time. In addition, an alternating monophasic stimulation is used to reduce charge injection while keeping the advantage of charge balancing of the biphasic stimulation. The BSN prototype has been assembled on two circular printed circuit boards of 2-cm diameter each. With a total rms power consumption of less than 15mW, the BSN can provide a stimulation current up to 2mA, with maximum pulse width of 210mus and a maximum frequency of 2kHz.

Fully-integrated inductive power recovery front-end dedicated to implantable devices

Wirelessly powered implantable biomedical devices require a near-field inductive link to provide enough power for high current stimulation of large electrode-nerve impedances. In that situation, the induced voltage may be much larger than the compliance of low-voltage integrated circuits, especially during low-load conditions. In fact, most power recovery approaches limit the voltage with an inefficient off-chip solution using discrete components such as a Zener diode or a shunt regulator, or even on-chip voltage clipping. In this paper, we propose the approach where the induced voltage is not limited at all, using a high-voltage (HV) CMOS technology. In order to fully integrate the inductive power recovery stage, we report the design of a HV custom integrated circuit (IC) that includes a full-wave rectifier and a 10 V regulator using a multiple-outputs voltage reference. The IC has been fabricated in DALSA-C08G technology and the total silicon area including pads is 4 mm2. This front-end stage can be driven by an input voltage as high as 50 V. Measurement tests are successful as the HV regulator shows good response to a power-on 50 V step, and good stability in presence of large input variations.

New Neurostimulation Strategy and Corresponding Implantable Device to Enhance Bladder Functions

Spinal cord injury (SCI) is one of the most complex and devastating medical conditions. Its worldwide incidence ranges from 11 to 112 per 100,000 Population (Blumer & Quine, 1995; DeVivo, 1997). SCI leads to different degrees of dysfunction of the lower urinary tract due to a large variety of possible lesions. Immediately after SCI, flaccid paralysis sets in, followed by the absence of reflexes and a complete loss of sensory and motor control below the level of lesion, rendering the urinary bladder areflexic and atonic. This period, termed spinal shock, can extend from a few days to several months (Chai & Steers, 1996). Most patients with suprasacral SCI suffer from detrusor over-activity (DO) and detrusor sphincter dyssynergia (DSD) (Blaivas et al., 1981). DSD leads to high intravesical pressure, high residual urine, urinary tract infection, and deterioration of the upper urinary tract. In order to recover the voluntary control of micturition, functional electrical stimulation (FES) has been investigated at different sites of the urinary system: the bladder muscle (detrusor), the pelvic nerves, the spinal cord and the sacral nerve roots. Among these, sacral nerve root stimulation is considered the most efficient technique to induce micturition and has been prevalent in clinical practice over the last two decades (Elabaddy et al., 1994). Using cuffelectrodes, this technique offers the advantages of a safe and stable fixation of electrodes as well as confinement of the spread of stimulation current within the targeted nerves. However, the detrusor and the external urethral sphincter (EUS) muscles share the sacral nerves as common innervations pathways, and stimulation of the entire sacral root induces contraction of both. Thus, the efficiency of micturition by means of sacral neurostimulation depends on the capability to contract the detrusor without triggering EUS contraction. In order to improve this neurostimulation selectivity, several techniques have been proposed, among which are rhizotomy, and EUS blockade using high-frequency stimulation. Dorsal rhizotomy consists of selectively severing afferent sacral nerve roots that are involved in pathological reflex arc in suprasacral SCI patients. Rhizotomy abolishes DO, reduces DSD, and prevents autonomic dysreflexia. As a beneficial result, the uninhibited bladder contractions are reduced, the bladder capacity and compliance are increased, urine flow is improved, and consequently the upper urinary tract is protected from ureteral reflux and hydronephrosis. In case of a complete SCI, dorsal rhizotomy is combined with an

Implantable neuro-monito-stimulation system dedicated to enhance the bladder functions

This paper concerns the design and implementation of a new implantable Neuro-Monito-Stimulation System (NMSS) for the urinary tract rehabilitation in paraplegics. In addition to selective stimulation for voluntary micturition and permanent stimulation for reduction of the detrusor overactivity, the NMSS includes telemetry capabilities of electrodes-tissues contact. Resistance up to 10 kOmega could be measured with good linearity and sent wirelessly to an external controller at 1 kbps data transmission rate. With an embedded rechargeable battery, the implant lifetime is significantly extended up to 1000 cycles of 250 hours with nominal operating conditions. The NMSS design is described with the main system solutions and the preliminary experimental results.

High-voltage DC/DC converter for high-efficiency power recovery in implantable devices

Implantable biomedical devices such as sensors and neurostimulators require a near-field inductive link to transmit power wirelessly. However, the near-field induced voltage is usually much larger than the compliance of low-voltage integrated circuit technologies. Thus most integrated power recovery approaches limit the induced signal to low-voltages with inefficient shunt regulation, or voltage clipping. We propose using a high-voltage (HV) CMOS technology to fully integrate the inductive power recovery front-end while adopting a step-down approach where the induced signal is limited to a much higher voltage (20 V). We previously reported a first IC that includes a HV rectifier and a HV regulator, which provide up to 12 V regulated DC supply from a 20 V maximum AC input. In this paper, we report the design of a second HV custom IC that completes the front-end by integrating an adjustable step-down switched capacitor DC/DC converter (1:3, 1:2 or 2:3 ratio). The IC has been submitted for fabrication in DALSA-C08E technology and the total silicon area including pads is 9mm2. Post-layout simulation results show that the DC/DC converter achieves more than 90 % power efficiency while providing about 3.9 V output with 12 V input, 1 mA load, 1:3 conversion ratio, and 50 kHz switching frequency.