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Biomedical circuits and systems to recuperate neuromuscular functions OUTLINE Biomedical circuits and systems to recuperate neuromuscular functions Main technological breakthrough of FES based SMDs w 1947, transistor allows circuit designs suitable for implants. w 1952, first external pacemaker which was the size of a table w Introduction n Mohamad Sawan, P. Eng., Ph.D., FCAE, Purpose and motivation radio of the time and was powered by 110 VAC. w Microelectronics activities Canadian Research Chair on Smart Medical Devices n PolySTIM Neurotechnology Laboratory n Dept. of Elec. Eng., École Polytechnique de Montréal [email protected] w 1957, electrical stimulation in the inner ear of the acoustic Design, construction & test of smart medical devices (SMDs) Typical architecture of an SMD n PART I n Neurostimulation to recuperate the bladder functions Intracortical neurostimulation to create vision for the blind Required biocircuits & biosystems Research team and collaborations Conclusions IEEE CASS DLP January 2004 2 M. Sawan w w w w Pacemaker: More than 350,000 pacemakers annually; Defibrillator: More than 50,000 implants annually; Cochlear implant: More than 50,000 people worldwide; Functional stimulation: Recuperate hands and legs movements of paralyzed patients; Stimulation for the treatment of Parkinson, respiration, pains, scleroses, etc; Automatic liberation of insuline in diabetics; Neuronal activities recording for better control; Devices for vision: Creation of adequate vision for blinds; Other implantable microsystems. Modulator Power supply n Low Pass Filter Efficiency and safety. Data transmission n n Manchester based codec PSK based codec: BPSK Demodulator (COSTAS Loop) m(t)sin(w1t+q1) • Recover the carrier and the data in the same loop -LSK: 200Kb/s -BPSK: 1Mb/s 7 Without Feedback: 12.03% With Feedback: 22.04% controller Power Amplifier On-Chip C1 Charge Pump 1 Voltage Regulator L1 L2 Charge Pump 2 Vdd Charge Pump 3 C3 C2 Charge Pump 4 Vdd1 Vdd2 Vdd3 Vdd4 Current sources DEMUX Signal Processor electrodes Clock Generator Load Shift Key (LSK) Encoder ADC MUX Analog frontend n Stimulation signals Data Demodulator - ETC impedance measurement - Charge per phase estimation - ETC voltage monitoring - Neural signal recording 5 Analog frontend 1 Controller/ Stimulator Electrodes External Controller Start-up Circuit Protection Circuit Clock Generator Circuit 6 M. Sawan • Lower urinary tract deficiency following a spinal-cord injury; • Conventional electrical neural stimulation (ENS) induces contraction on both detrusor and sphincter, thus preventing from complete voiding; - Incontinence and/or retention. • Conventional ENS combined with nerve rhizothomy is not accepted by patients; • Multiples complications at several levels (Sphincter, bladder and kidneys) due to repetitive catheterizations; Q branch • Transfer rate: • PSK demodulator consumes only 529 mW. •QPSK may double the data rate. Off-Chip Vdd The bladder controller: Dual-stimulator m(t)sin(q 1-q 2) • Full duplex mode Implant Circuit Switching Regulator Data Modulator The bladder controller: Dual-stimulator Data Out m(t)sin2(q1-q 2) 2 Low Pass Filter ASK Demodulator / DAC/Decoder Battery Test stimuli Returned informations Low Pass Filter Phase Shifter 90 data Measurement and digitalization circuitry Data processing 2cos(w1t+q2) Link features M. Sawan VCO Clk Main Physiological stimuli MUX 2sin(w1t+q 2) Data In Par Stimuli generator Back telemetry Demodulator RF LINK to Transfer Power & Data (cont’d) h total = h rflink ⋅ h rectifier ⋅ h regulator Receiver Skin Power Transfer Global view h = h ⋅ h total rflink rectifier ⋅ h regulator Implant External controller M. Sawan I branch m(t)cos(q1-q2) Proposed SMD topology (cont’d) Bi-directional RF link Features: 4 M. Sawan 3 M. Sawan Proposed topology (Cont’d) w nerve in a totally deaf human was reported. 1960, totally implanted pacemaker (Buffalo). 1961, peroneal nerve stimulator for foot drop in hemiplegics. 1968, implantation of an electrodes array on the visual cortex. 1980, first microchip was used to design small pacemakers. 1984, FDA approved the first cochlear implant for adults 1991, recording of neural activities 1992+, FES is widely used in several applications. Smart medical devices Main technological breakthrough w w w w w w w w w w w Focus on two main case studies • Early ENS tends to reduce the hyperreflexia phase, while limiting damage in the whole urinary system; • Bladder hyperreflexia (hypertrophy or atrophy) hardly curable with traditional medicine; • Selective neural stimulation proposed by our team allows efficient voiding of the bladder; Electrical stimulation of the detrusor muscle allows partly voiding and may induce kidney complication. • M. Sawan 8 • Permanent low frequency combined with selective stimulation are proposed by our team to improve bladder function. M. Sawan 9 1 The bladder controller: Dual-stimulator Selective neural stimulation The bladder controller: Dual-stimulator Selective neural stimulation First selective stimulator includes : l • Selective stimulation allows improvement in voiding; • This technique diplexes high and low frequency stimuli to activate both categories of sacral nerve fibres: The bladder controller: Dual-stimulator Permanent/Selective stimulations l ‡ Implant of 3.5 cm of diameter built around field programmable Proposed dual-stimulator includes : -Permanent LF stimulation : Low amplitude train: - Prevent the bladder hyperreflexia Lesion - Maintain the bladder shape Skin - Selective stimulation. devices (FPD) and other discrete components; ‡ Shape Memory Alloy (SMA) based cuff electrodes to facilitate connecting to sacral roots; ‡ User friendly external controller based on FPD and other discrete components. - HF stimuli for somatic fibres which innervate the sphincter. - LF stimuli for parasympathetic fibres which innervate the detrusor. Selective Implantable Stimulator User Interface RF Emitter l Toff - Battery to power the permanent stimulator; - RF link for the selective stimulation. 1/Freq Amp 11 M. Sawan RF_PWR Switch #1 RF_PWR_EN Antenna Decoder BAT_PWR G_CLOCK Controller #1 (FPGA) Bus Controller DIN/SCLK/CS 3 UP/DOWN READY DIN/SCLK/CS Switch #2 BAT_PWR_EN 2 3 Battery SYS_ON SYS_OFF DSR Switch #3 Evolution w 1960s, few groups began to investigate the possibilities of exploiting the phenomenon of creating points of lights; w 1990s, Researchers at NIH demonstrate that intra cortex 12% Voiding by selective stimulation UP/DOWN 2 SYS_ON The visual cortical stimulator Results Intravesical and intraurethral pressures measurements and Electromyographic (EMG) recording of the pelvic floor muscles were performed. l SWT_PWR Z_CTRL Am Demodulator DATA_IN MANCH_IN 12 M. Sawan Bladder dual neurostimulation: The bladder controller: Dual-stimulator Implant description 250 ml stimulation allows to generate phosphenes; 88% PIC_PWR Bladder The system includes: PW 10 Dual-stimulator Implant External Controller Ton M. Sawan Bipolar cuff Electrode Power Data Param Stim #5 30Hz 175us 0.9mA SMA Electrode Cuff 200 ml Mean Bladder 150 ml Volume PIC_PWR w Progress in microelectronics and microfabrication motivate Residual researchers to explore several approaches; 66% 100 ml Voided 34% DSR READY SYS_ON 31% BAT_PWR_EN cath SWT_PWR 3 UP/DOWN 2 DAC Current Source Current Commutator n n 14 M. Sawan n n n n n n n n M. Sawan n n n n n n n n M. Sawan n n n n Fixed, stable phosphenes Many phosphenes with few electrodes Phosphene characteristics widely variable. Tongue stimulation, and auditory or tactile input. 17 Better resolution Better control on phosphenes Lower power Lower chances of seizure. Subject: 38 year old woman Images feed from a digital camera to a beltmounted processor; commands send through the skull, and into the visual cortex Optic nerve stimulation Artificial retina requires functional retina and optic nerve; Surface stimulation of the visual cortex is imprecise; Other techniques only allow sensory substitution . 16 Intra-cortical stimulation Stable, non flickering phosphenes; Able to distinguish shapes; Lower threshold in macular region; Resolution restricted by electrode shape Mechanical properties challenges. Extracortical surface stimulation n Intracortical stimulation does not depend on the health of the eye or optic nerve; also, it requires stimuli at low current level. It can be the predominant one: n 15 Intracortical stimulation Experimentation n Artificial retina; Cuff electrodes around the optic nerves; Tongue stimulation; Surface stimulation of the visual cortex; Intracortical stimulation of the visual cortex. Early 2000, a prototype has been completed to prove the feasibility of a visual cortical stimulator Miniaturized implant version is being achieved. M. Sawan Artificial retina / Extracortical stimulation Researchers worldwide are developing solutions Several approaches are being explored: n cath External controller Subcutaneous Implant (~ 2.5cm) One cuff electrode pair Approaches n LF+HF LF +permanent w We start this project in 1996 The visual cortical stimulator n LF Nerve 13 M. Sawan holding a PC which drives a percutaneous connector toward the skull to extracortical visual region; 0 ml SYS_OFF DIN/SCLK/CS • • • w Dobelle institute, New York, early in 2000 presented a patient 69% 50 ml RF_PWR_EN Controller #2 (PIC) Parameters affect brightness, not position Elicits stable phosphenes Threshold ~15 µA (as low as 1.9 µA) Short term accommodation. Experiments in Monkey at IIT n M. Sawan Recently, report good news. 18 2 The visual cortical stimulator Integrated smart devices Prototype (VCS) Tx Rx Stimulator • Block diagram Interface Timing Hardware 5 Antenna 6 Controller Chip n n 19 20 M. Sawan The visual cortical stimulator n n Stimulator Modules (SMs) Current Constant Stimulation w Monopolar, Bipolar w Single/Multiple paths n stimulator monitoring w One to 25 bits per pulse. Interface Module (IM) Enables the use of a LF Clk w System power saving w Bidirectional wireless Communication n n w A/D Conversion of monitoring data Interface Module n Analog out n REF n Compatible with electrode matrix dimensions n n 23 Downlink Communication Downlink Tradeoff VDD High Q > Best efficiency, but Sampling at any programmable time Voltage measurement n Current monitoring Coil Voltage n Digital decoder I monit SS Current Monit. REF REF j Dig. Dir I n Dig. Att In w Toggling of attenuated carrier detected by From Ctrler enable adcclk adccvt To Ctrler adcout Normal Stim. + - Hi-Z DAC DAC DAC DAC Voltage Monit. Distributed reference Bipolar Current sink Current sink/source Current source • Modular: Variable number of stimulation sites R2R • Stimulation modes: Mono / Bipolar, Single / distributed return terminal REF • Electrical Isolation: Allows stimulation current / voltage monitoring. Hi-Z M. Sawan clk(N) – Safety ADC extra toggling of direct carrier. 25 clk(1) clk – Flexibility V DD VSS VthL Lsk clk cvt FSM R2R REF j VthH V -V w Based on carrier signal attenuation M. Sawan Distant reference Contr oll er DD ctrl / statusreg errflg Contr oll er Analog Monit. Bus V +V Direct Coil Att. Coil by reducing carrier OFF period. data(N) Monopolar Hi-Z than ~500 kbps @ 13.56 MHz. data(1) in/ out reg LSK out Anodic/Cathodic Stimulation … Limited Data Rate w Enhance Data Rate & Power Transfer (toin/out FSMand err c trl / statusreg) in/out FSM Stimulus mode/type w Actual stimulation current measurement. w Manchester encoding does not allow more error detec. Cortical stimulation w Any stimulation site during normal stimulation limited by Q-factor of receiver when rectifier diodes voltage is reversed. n n n w Envelop transition speed data clk 24 M. Sawan V / I monitoring ASKin Manch. decod. Actual Stimulating Current Voltage at every stimulation site Monitoring & Data uplink Power Efficiency vs Data Rate n n M. Sawan Clk Clk Data Data ext. Env. det. Envelop env detect. Monitoring w 4 x 4 electrodes (prototype) PWR data(N), clk(N) Vmon(N) err(N) Controller w Manchester LSK n RAM Configured Parameter continuous error checking LSKout Uplink Power management In Communication Error detection/correction Stimulator Instructions Dispatching PWR data(1), clk(1) Vmon(1) err(1) LSK mod ASKin System Control Voltage Monitoring w Disables stimulation in case of 22 F RE (Tx/Rx), but need higher data rate w «All digital» Demodulator n Monit. Regul Downlink w ASK: keep OOK for its simplicity Band-Gap Bias R2R External Coil, Rectifiers Communication Electrode Switch Matrix Parameter corruption M. Sawan Implant Electrodes Stim. Module 21 n w Implant control w Power recovery / management Interface Module Implant architecture DAC DAC DAC DAC #0 #1 #2 #3 LS Serial in clk Configurable Comm. protocol Display Stim. Module Power supply Features (flexibility/safety) w Multi-channel stimulation w Electrode-tissue and n Transmitter Stimulator Module Components of Multi-modules Inverse Stim. Site to PVC Mapping Display Implantable components M. Sawan Implant architecture Implant architecture PVC to SSA mapping Ordering Encoding & timing Low Level Data Manag. Front-end for efficient image processing; Tx / Rx for power efficiency and data rate; Power consumption, size, safety, biocompatibility; Interface for shape and surface. VDB source Visual Field Emulator Artificial Visuotopic Map gen. Image fitting SSA to PVC mapping Low level Pulse sequencing Implanted Components LS M. Sawan PVCS emulating a 16x16 matrix Matrix of electrode s & 101100010 1 Direct Mapping S kin n n Config. Interface System level optimization: Camera mounted onto a pair of glasses; External controller to process the images and commands; Bidirectional data & energy transmitted by RF link; Implant to stimulate the region of the cortex controlling vision. Programming GUI Visuotopic Map ... n Image enhancement ... n Stimulator Image acquisition ... n Development board External Components The system includes 4 main components: n Isolation Con tr oll er 3 Image Processor & Power source Compute r LS 1 Input Image Data collected from experimentation External components Inputs RF Data and Power 4 Wireless Transmitter ... Front-end (Camera & DSP) F MRE 7 Stimulator Chips adc lck adc cvt Cortex 2 Camera The visual cortical stimulator Undertaken research projects The whole proposed system adc out The visual cortical stimulator 26 M. Sawan 27 3 Stimulation Module (4 ( x 4 Matrix) • Implant assembly n Modular DACs TEST structures CMOS 0.18 µm, ~60 000 Gates BIAS Downlink n > 1 Mbps @ 13.56 MHz, Duty Cycle = 67% 500 kbps @ 13.56 MHz, Duty Cycle > 85% n 400 um > 100 mW load capability; P (err) < ELECTRODES CONN / CTRL n MONITORING R2R AMP Amplitude, Pulse width, Inter-phase delay, Direction of first pulse, Pulse frequency, Pulse train duration, and Intertrain delay. Physical Dimensions Wireless Data rate >1 Mb/s Sufficient for 1000 stimulation sites n Parameters IM Power/data link CTRL Power: <1mW/SM @ 1MHz n One controller & several stimulation Units Collaboration with the INM SMs Flexible substrate Uplink : 200 kb/s 10 -6 In vivo testing Cortical stimulation Implementation Results 256 stimulation patterns @ 50 Hz. n Max. Stim. Freq. : > 1 kHz @ 500 Elec. I / V Monitoring n SM’s area : 3.5x3.5 mm2 n Substrate : 50 µm n Stim Assembly: 1 mm thick n Electrode Length: 2 mm n IM’s Area : ~ 2 x 2 cm2 n Ctrler thickness : ~ 3 mm. Comput 28 Implant M. Sawan Downlink Timing Electrode matrix 400 µm spacin; Platinum tips; ParyleneC coating, Low Impedance. n Physical Properties Safety Data rate Stimulation Flexibility Power efficiency n Placement flexibility, wiring Chronic usage High number of stimulation sites Prototype High parallelism n n n Acquired Image n n Irregular - Density - Size - Sensitivity -… n Fit 34 weighted with Schwartz retinotopic relationship and estimated electrode placement. n Zones Probabilistic weighted PVFC variations and phosphene parameters: 33 M. Sawan Image acquisition/processing Power Optimization Fovea Required stimulation current for 1 sample frame Min. Current Summary n n Fixed Scan average 35 Design of dedicated image sensor High voltage stimulation techniques Modeling, simulation and in vivo validation Measurement techniques of neuronal activities Assembly several arrays n 128, 500, and 1000+ microelectrodes. Nanoelectronics will allow the design of additional devices. Microelectrodes & power sources are among the major works. Such medical devices include validation and involve physicians, engineers, health care professionals, families, etc. Max. Current M. Sawan Stimulation in the visual cortex may soon permit true artificial vision Other undertaken research topics: w w w w w Total stimulation current Adaptive Scan average Edges Typical topology of inductively coupled implantable electronic devices Dual-stimulator to recuperate the bladder functions Main issues of a visual cortical stimulator With large electrode arrays, stimulation current represents a major part of power consumption n Predetermined image scanning results in large current variations n Adaptive scanning method regulates current demand Fitting example M. Sawan Original w Set of Phosphene Visual Field Coordinates w Generated from probabilistic parameters w Equalize the required power and reduce the peak demands Horizontal Angle or from Realistic Visuotopic Map w Sensitivity, Size, Brightness, etc. Vertical Angle n w Investigation of representation needed for a VCS. n 32 M. Sawan Sample Visuotopic Map Image has to be enhanced for clarity, then mapped to the available PVFCs. The Visual Field Emulator allows perception prediction / evaluation from the research team. Experimental determination Creation of random maps : Constructed from experiments Visual Data Base Generator Minimize power consumption with other techniques than circuit optimization approaches. Visual Data Base (cont’ (cont’d) n n Present image as the patient would see it; Hardware implementation of processing algorithms; Low power consumption topologies. Image acquisition/processing Enhancement/mapping n Actual Perceived Image (Direct Fit) 31 M. Sawan Allow to transform images over visuotopic maps; Follow a bottom-up approach until percepts are understandable; Must deal with every image encountered in real world; Be safe for patient. Required processing Low resolution Control on phosphene parameters Electrically invoked phosphenes w Visuotopic Maps Dedicated image processor External Control w Relevance of Data Image acquisition/processing Main specifications Challenges and Need for Optimization n Stimulator Subject (Monkey) 30 M. Sawan Image acquisition/processing Image acquisition/processing w w w w w 29 Stimulator Only electrodes in subject; Configurable hardware; “Large” output voltage swing. Stim. Units. M. Sawan Oscilloscope Development board Assembly n PWR Data Isolation er t M. Sawan 36 4