Power and data managements

Transcription

1 GBM830 Dispositifs Médicaux Intelligents Power and data managements Part : Inductive links Mohamad Sawan et al Laboratoire de neurotechnologies Polystim!! mohamad.sawan@polymtl.ca! M548! April 03

2 Inductive link : Outline 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 Modulation and demodulation Batteries Miniature, rechargeable, etc. GBM830 - Dispositifs Médicaux Intelligents

3 Power and Data Link : Typical architecture External controller Receiver Test stimuli Stimuli generator Modulator Demodulator AC/DC Supply Main Controller Current sources Data processing Back telemetry Measure & digitize MUX DeMUX Skin Electrodes GBM830 - Dispositifs Médicaux Intelligents 3

4 Power and Data Link : Multisensing devices Electrical Impedance Pressure Implantable Wireless Sensor Microsystem Analog to Digital Converter RF Transmitter/ Receiver... Data transmitted to a Base Station outside of the body ph MUX Digital Control Unit Modulator & Demodulator Temperature NO or O Concentration Power Regulation GBM830 - Dispositifs Médicaux Intelligents 4

5 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 : MEMS, Vibration, RF Downlink Battery GBM830 - Dispositifs Médicaux Intelligents 5

6 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 M * * L L C R V rec C3 Voltage Regulator LOAD V DC inductive link rectifier linear regulator GBM830 - Dispositifs Médicaux Intelligents 6

7 Inductive Powering : Choice of Carrier Frequency Two major limits: ) Coil self-resonance frequency, ) EM energy absorption in tissue When EM waves propagate through body tissues (skin, bone, fat, body fluid) to reach the receiving antenna, they are attenuated along the way. K = - exp (- d / Δ) d is tissue thickness. D is tissue skin depth. More power loss in the power transmission and conditioning circuitry at higher frequency For MHz < f c < 0MHz, average density of electromagnetic power absorption in tissue increases as f Carrier Frequency f c ~ Penetration depth D GBM830 - Dispositifs Médicaux Intelligents 7

8 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 (MHz) Maximum Power Density (W/Cm ) If f c equals 5.MHz 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. GBM830 - Dispositifs Médicaux Intelligents 8

9 Inductive Powering : Coils coupling factor External coil is driven by an RF amplifier at a suitable frequency. Secondary coil captures a portion of the EM field, inducing a current. Captured energy by the secondary coil depends on coupling factor, K. 0 < K < ; dimensionless; Typical values are K = r implant r r implant r reader reader ( x + rreader ) 3 Vs ~ R C M * * L L C R V rec C3 Voltage Regulator LOAD V DC inductive link rectifier linear regulator 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. GBM830 - Dispositifs Médicaux Intelligents 9

10 RF Inductive Powering : System View Model of the inductive link front-end. R = parasitic resistance; C = tuning capacitance; and R L = system load. L and L represent a weakly coupled transformer. L i = / n = k / L n i V L V L = V + (R + jwl ).( R L + jwc ) i V = jwk L ( i n / ) = jwk L L.i V V L = wk L L i = Aki ( wl R L + wr C ) + ( w L C + R R L ) GBM830 - Dispositifs Médicaux Intelligents 0

11 RF Inductive Powering : System View We require V L to be within a certain range. k is a factor of the distance between the coils. Example: L L C R R L f 43.5 uh 3.7 uh 330pF k 4MHz V L = wk L L.i ( wl R L + wr C ) + ( w L C + R R L ) = Aki V L = 70.k.i At a fixed distance, the voltage on the implanted coil can be adjusted by changing the current in the primary coil. GBM830 - Dispositifs Médicaux Intelligents

12 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. Vs ~ R C M * * L L C R V rec C3 Voltage Regulator inductive link rectifier linear regulator LOAD V DC Power conditioning circuitry such as integrated voltage rectifiers and regulators are also needed to generate a clean dc power supply. Primary resonant signal Secondary induced signal Rectified voltage (half rectifier) Regulated voltage supply GBM830 - Dispositifs Médicaux Intelligents

13 Inductive link : Power transfer efficiency Vs ~ R C M * * L L C R V rec C3 Voltage Regulator LOAD V DC inductive link rectifier linear regulator = Z r = rflink Z k R C ν ν ν R C + k R C rectifier = V rect V rect V rect + V diode regulator V DC GBM830 - Dispositifs Médicaux Intelligents 3

14 Inductive link : Power transfer efficiency (Cont d) Data Modulator External Controller PA C Skin Implant Rectifier Battery L L C Shunt regulator To/From other parts η total = = k C VDC R C P load + k C (V rect + V diode ) V DC k VDC R P load + k (V rect + V diode ) V DC V rect = = R C R k C kr + k C + k R V R RC s V s GBM830 - Dispositifs Médicaux Intelligents 4

15 Inductive link : Power transfer calibration External Implant Data In Data Out ASK Demodulator data direction Data Encoder R C Vs + - * M * L L C R a R b Battery External Controller Data Modulator PA Switching Regulator Vdd ASK Demodulator / DAC/Decoder C L Skin L Implant Rectifier C Load Shift Key (LSK) Shunt regulator Encoder ASK/PSK Demodulator To/From Other parts Power regulation at k=0.07, V REGDC =.8 V. GBM830 - Dispositifs Médicaux Intelligents 5

16 Inductive link : Power transfer calibration (Cont d) mw I I I I I I V 0 V mw 5 mw mw mw Pload η total = = R C P R P load load + + k k ( V k C k V rect V ( V DC DC C rect + V + V diode diode ) V DC ) V DC Power Efficiency Versus Load Power W/O Feedback W Feedback Voltage of Secondary Coil Versus Load Power W/O Feedback W Feedback GBM830 - Dispositifs Médicaux Intelligents 6

17 Inductive link : Power transfer calibration (Cont d) Carrier Frequency : 3.56 MHz. Transmission Mode : Full Duplex. Modulation Methods : Uplink LSK), 00 kbps Downlink BPSK, Mbps. GBM830 - Dispositifs Médicaux Intelligents 7

18 Inductive link : Linear Voltage regulator To increase the power efficiency, low dropout voltage (LDO) regulator is used. Vin Bandgap Voltage Reference.6 V Vref Passing transistor + OPAMP Power loss - Vout R LOAD Advantages of linear regulator - Able to be fully integrated - Less noisy. Drawbacks - Low power efficiency - Only step-down DC-DC converter feasible. R GBM830 - Dispositifs Médicaux Intelligents 8

19 Inductive link : Linear voltage regulator LDO regulators with dual-voltage output SC DC-DC converter Vin_boost Vin Bandgap Reference NM + V g Error Amp - V OH + V M g Error Amp - V OL R b 3.3 V.8 V R b4 Native NMOS transistor: Skips the thresholdvoltage adjustment implant process. R b R L R b3 R L V-I charts of the native NMOS passing transistor (W/L= 400/.) GBM830 - Dispositifs Médicaux Intelligents 9

20 Inductive link : Voltage regulation front-end V rec 3.3V regulator.8v regulator LOAD V L V H I H V rec Parallel/Cascade two linear regulators 3.3V regulator LOAD V H I H.8V regulator LOAD V L I L LOAD I L Coil Resonance circuit & Full-wave rectifier V rec = 3.6 V, V recl =. V V recl SC step up DC-DC converter Start-up Circuit Integrated on chip Bandgap Reference 3.3 V LDO regulator V ref.8v LDO regulator V high V low Stimulator Output Stages & Other Circuitry 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% GBM830 - Dispositifs Médicaux Intelligents 0

21 Inductive link : Circuits of the voltage regulator Vin SC DC/DC converter M5 M3 The CMOS bandgap reference M M A Vout Vin MP05 MP06 MP09 MP5 B C C M6 M4 Cout MP07 MP08 MP0 MP MP6 CLK CLK non-overlapping clock generator C Vout Start-up circuit MN03 MN04 MN3 MN M 5 M 6 MN0 MN0 MN4 R M 7 V out R M 8 Q Q Q3 Q4 Q5 M M M 4 M 3 V in V in VSS GBM830 - Dispositifs Médicaux Intelligents

22 Power and Data Inductive ink : Voltage regulator The power recovering chip SC DC/DC converter LDO regulators GBM830 - Dispositifs Médicaux Intelligents

23 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 PMOS 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. GBM830 - Dispositifs Médicaux Intelligents 3

24 Inductive link : Fully integrated solutions Block a Block c R C T4 RF input signal D D C C C R T T3 T5 C L Digital output Block b T T4 T5 T7 T9 T T T3 T6 T8 T0 R R R L DC output GBM830 - Dispositifs Médicaux Intelligents 4

25 Inductive link : Power link V Out C L R L V AC Gnd V DD V AC C L R L V SS GBM830 - Dispositifs Médicaux Intelligents 5

26 Inductive link : Data transmission, up link Data in Switch Off D C D D D 3 D 4 RL C D3 D RL D4 Switch On Req= RL/ D4 LSK Modulation C D3 RL 00 kb/s 00 kb/s R eq = R L /8 GBM830 - Dispositifs Médicaux Intelligents 6

27 Inductive link : Power link GBM830 - Dispositifs Médicaux Intelligents 7