Power and Data Link : Typical architecture. April External controller Receiver. Test stimuli. Stimuli generator. Modulator

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1 April 0 Introduction Power and data links Inductive link Choice of carrier frequency Transmitted power limits Inductive system modeling Conditioning and calibration techniques Discrete and integrated circuitries Power transfer Up and downlinks data transmission odulation and demodulation Batteries iniature, rechargeable, etc. GB830 - Dispositifs édicaux Intelligents Power and Data Link : Typical architecture External controller Receiver Test stimuli Stimuli generator odulator Demodulator AC/ Supply ain Controller Current sources Data processing Back telemetry easure & digitize UX DeUX Skin Electrodes GB830 - Dispositifs édicaux Intelligents 3

2 Power and Data Link : ultisensing devices Electrical Impedance Pressure Implantable Wireless Sensor icrosystem Analog to Digital Converter RF Transmitter/ Receiver... Data transmitted to a Base Station outside of the body ph UX Digital Control Unit odulator & Demodulator Temperature NO or O Concentration Power Regulation GB830 - Dispositifs édicaux Intelligents 4 Embedded medical devices : Power supplies Power sources Transcutaneous RF inductive powering : Implants, no internal power source Primary (non-rechargeable) batteries : Wearable systems; Low-power design Secondary (rechargeable) batteries : Implantable systems w/ RF inductive link Fuel cells: Rechargeable electrochemical energy converters Electricity/heat generation from reaction of Hydrogen and Oxygen No pollution since water is the main by-product. Energy scavenging and power harvesting : ES Downlink! Battery! GB830 - Dispositifs édicaux Intelligents 5 Transcutaneous link : RF Inductive Powering Inductive powering is a common method for providing energy to implantable wireless devices. For systems having large power consumption or requiring long lifetime External coil is usually driven by a transmitter operating at a suitable frequency to provide adequate power to the device. Vs ~ R C R * * L L C C3 Voltage Regulator V inductive link rectifier linear GB830 - Dispositifs édicaux Intelligents 6

3 Inductive Powering : Choice of Carrier Frequency Two major limits: ) Coil self-resonance frequency, ) E energy absorption in tissue When E waves propagate through body tissues (skin, bone, fat, body fluid) to reach the receiving antenna, they are attenuated along the way. K - exp (- d / ) d is tissue thickness. D is tissue skin depth. ore power loss in the power transmission and conditioning circuitry at higher frequency For Hz < f c < 0Hz, average density of electromagnetic power absorption in tissue increases as f Carrier Frequency f c ~ Penetration depth D GB830 - Dispositifs édicaux Intelligents 7 Inductive Powering : Transmitted Power Limits IEEE has recommended a standard for safety with respect to RF exposure. For biomedical implantable systems, RF powering occurs within a controlled environment. Frequency (Hz) aximum Power Density (W/Cm ) If f c equals 5.Hz and the transmitter coil has a diameter of 0mm, the transmitted power has to be less than 6W. The received power is then determined based upon the inductive link configuration and telemetry distance. GB830 - Dispositifs édicaux Intelligents 8 Inductive Powering : Coils coupling factor External coil is driven by an RF amplifier at a suitable frequency. Secondary coil captures a portion of the E field, inducing a current. Captured energy by the secondary coil depends on coupling factor, K. 0 < K < ; dimensionless; Typical values are K r r r implant reader 3 implantrreader ( x + rreader ) Vs ~ R C R * * L L C Voltage Regulator C3 V inductive link rectifier linear K is an important factor in the operation of any inductively coupled system r i & r r are the radii of the two coils with x being the distance between them. Assumptions: coils are parallel and center-aligned with only air between them. GB830 - Dispositifs édicaux Intelligents 9 3

4 odel of the inductive link front-end. R parasitic resistance; C tuning capacitance; and system load. L and L represent a weakly coupled transformer. L i i / n k / L n V + (R + jwl ).( + jwc R ) L i V V jwk L ( i n / ) jwk L L.i wk L L i ( wl + wr C ) + (! w L C + R ) Aki GB830 - Dispositifs édicaux Intelligents 0 RF Inductive Powering : System View We require to be within a certain range. k is a factor of the distance between the coils. Example: L L C R f 43.5 uh 3.7 uh 330pF k 4Hz wk L L.i ( wl + wr C ) + (! w L C + R ) Aki 70.k.i At a fixed distance, the voltage on the implanted coil can be adjusted by changing the current in the primary coil. GB830 - Dispositifs édicaux Intelligents RF Inductive Powering : Conditioning Circuitry But, this is clearly not enough! Received voltage across the secondary coil is a sinusoidal voltage with little or zero dc value. Power conditioning circuitry such as integrated voltage rectifiers and s are also needed to generate a clean dc power supply. Vs ~ R C Primary resonant signal * * L L C R inductive link rectifier linear Secondary induced signal C3 Rectified voltage (half rectifier) Voltage Regulator Regulated voltage supply V GB830 - Dispositifs édicaux Intelligents 4

5 Vs ~ R C R * * L L C C3 Voltage Regulator V inductive link rectifier linear Z k R r C rflink Z R C + k R C t rectifier t + V diode! V t GB830 - Dispositifs édicaux Intelligents 3 Inductive link : Power transfer efficiency (Cont d) External Controller C Data odulator PA Skin Implant Rectifier Battery L L C Shunt To/From other parts! total k C V R C P load + k C (t + V diode ) "V k V R P load + k (t + V diode ) "V V rect k C! C R V s R C + k R C kr V s R + k R GB830 - Dispositifs édicaux Intelligents 4 External Implant Data In Data Out ASK Demodulator data direction Data Encoder R C Vs + - * * L L C R a R b External Controller C Skin Data PA odulator Vdd L Switching L Battery Regulator ASK Demodulator / DAC/Decoder Implant Rectifier C Load Shift Key (LSK) Shunt Encoder ASK/PSK Demodulator To/From Other parts Power regulation at k0.07, V REG.8 V. GB830 - Dispositifs édicaux Intelligents 5 5

6 I I I I I V V 0 I mw mw 5 mw mw mw Pload k V C " total RC Pload + k C( Vrect + V diode)! V k V RP load + k ( Vrect + V diode)! V Power Efficiency Versus Load Power W/O Feedback W Feedback Voltage of Secondary Coil Versus Load Power W/O Feedback W Feedback GB830 - Dispositifs édicaux Intelligents 6 Carrier Frequency : 3.56 Hz. Transmission ode : Full Duplex. odulation ethods : Uplink LSK), 00 kbps Downlink BPSK, bps. GB830 - Dispositifs édicaux Intelligents 7 To increase the power efficiency, low dropout voltage (LDO) is used. Vin Bandgap Voltage Reference.6 V Vref Passing transistor + OPAP Power loss - Vout R Advantages of linear - Able to be fully integrated - Less noisy. Drawbacks - Low power efficiency - Only step-down - converter feasible. R GB830 - Dispositifs édicaux Intelligents 8 6

7 LDO s with dual-voltage output SC - converter Vin_boost Vin Bandgap Reference N + V g Error Amp - V OH + V g Error Amp - V OL R b 3.3 V.8 V R b4 Native NOS transistor: Skips the thresholdvoltage adjustment implant process. R b R b3 V-I charts of the native NOS passing transistor (W/L 400/.) GB830 - Dispositifs édicaux Intelligents 9 3.3V.8V V H I H Parallel/Cascade two linear s 3.3V V H.8V I H I L I L Coil Resonance circuit & Full-wave L rectifier SC step up - converter Start-up Circuit 3.3 DO Bandgap V ref Reference V high Stimulator Output Stages & Other Circuitry 3.6 V, L. V Integrated on chip.8do V low Load current I L (.8V) Stimulation current I H (3.3V) Delivered Power Power losses Normal Proposed Efficiency Normal Proposed 5 ma.6 ma 4.8 mw 9.48 mw.94 mw 60.6% 8.9% GB830 - Dispositifs édicaux Intelligents 0 Inductive link : Circuits of the voltage Vin SC / converter 5 3 The COS bandgap reference A Vout Vin P05 P06 P09 P5 B C C 6 4 Cout P07 P08 P0 P P6 CLK CLK non-overlapping clock generator C Vout Start-up circuit N03 N04 N3 N 5 6 N0 N0 N4 R 7 V out R 8 Q Q Q3 Q4 Q5 4 3 V in V in VSS GB830 - Dispositifs édicaux Intelligents 7

8 The power recovering chip SC / converter LDO s GB830 - Dispositifs édicaux Intelligents RF Inductive Powering : Conditioning Circuitry Rectifiers: They rectify the incoming sinusoidal signal either in every cycle (fullwave rectifier) or in every other cycle (half-wave rectifier). Half- Wave Full- Wave In each cycle (positive or negative), only POS transistors conduct. An external capacitor is also used for lowpass filtering the rectified signal to reduce its ripple. Practically, integrated full-wave rectifiers are more complicated than this. Additional devices should be incorporated to protect the main transistors against high voltage and to reduce the possibility of latch-up. GB830 - Dispositifs édicaux Intelligents 3 Inductive link : Fully integrated solutions Block a Block c R C T4 RF input signal D C C D C R T T3 T5 C L Digital output Block b T T4 T5 T7 T9 T T8 T T6 T0 R R output T3 GB830 - Dispositifs édicaux Intelligents 4 8

9 V Out C L V AC Gnd V DD V AC C L V SS GB830 - Dispositifs édicaux Intelligents 5 Data in Switch Off D C D D D 3 D 4 RL C D3 D RL D4 Switch On Req RL/ D4 LSK odulation C D3 RL 00 kb/s 00 kb/s R eq /8 GB830 - Dispositifs édicaux Intelligents 6 GB830 - Dispositifs édicaux Intelligents 7 9