1. Biotelemetry: A Review of the Art and Some Interesting Circuits for Low-Power, Low- Noise Frequency Synthesis Ron Spencer, Ph.D. Postdoctoral Candidate Seminar September 25, 2003

2. September, 25, 2003The Krasnow Institute Seminar Preview n Biotelemetry: What is it and why use it? n Prior Work & Typical Specs n Basic architecture of Telemetric Transceiver n Power Reduction Strategies n Data Conversion (using converters) n Frequency Synthesis: - PLLs - VCOs (using magnetic coupling) - Frequency division (using injection-locking) n Summary

3. September, 25, 2003The Krasnow Institute Seminar What is it and why would you use it? n Necessity - Implantable prosthetics - retinal, cochlear, pacemaker - Animal tracking - freedom of movement n Quality of measurement - tethering forces on electrodes n Convenience - Multi-electrode stimulation/recording - Vital sign monitoring in critical situations Why Use It? Biotelemetry is the wireless transmission of automatically measured physiological data from the point of sensing to a remote location. However, in practice the term also refers bidirectional wireless data transfer and remote powering.

4. September, 25, 2003The Krasnow Institute Seminar Applications n Neuroprosthetics (neurostimulation) n Multi-electrode recording n Vital sign monitoring in critical and ambulatory care n Vital sign monitoring of pilots and astronauts n Remote wildlife monitoring and tracking (avian, fish, mammals, reptiles - activity, depth, altitude, temperature, mortality) n Temperature n EMG, Motor activity n EEG n ECG, Heart rate n EOG n Pressure (e.g. arterial, venous, left ventricular, intra-ocular, bladder, & kidney) - Transoma Medical Measurements Mini Matter: Pediatric to geriatric, mice to men, miniaturized [biotelemetry] products from Mini Mitter are appropriate for all research subjects.

5. September, 25, 2003The Krasnow Institute Seminar Wearable Devices Mini Mitters Actiwatch TM - Medical diagnostics Mini Mitters Actiwear TM - Periodic Limb Movement for diagnosing sleep disorders Mini Matters Actical TM - Accelerometer for diagnosing obesity, nutrition, exercise, and rehabilitation Externally worn devices do not need to be extremely low- power.

6. September, 25, 2003The Krasnow Institute Seminar Commercial Devices for Physiological Monitoring Mini Mitters Vital View TM Body Core Temperature Heart Rate Gross Motor Activity Running Wheel Turns Drinking/Licking Frequency Feeding Behavior Ambient Temperature Ambient Light Implantable transmitters (temperature and gross motor movement) Implantable e-mitters (heart rate and movement monitoring) Receiver Companies: Biotelemetrics, Inc. Kent Scientific Mini Mitter Spacelabs Transoma Medical (formerly Data Sciences Intl.)

7. September, 25, 2003The Krasnow Institute Seminar Prior Work n Monitoring and Recording n Neurostimulation n Sieve electrode recording (Akin et al.) n Sympathetic nerve activity and ECG measurement (Enokawa, et al.) n Auditory experimentation (Lukes, et al.) n Monitoring of freely moving animals and insects n Single neuron discharge in monkeys n Retinal prosthesis - retinitis pigmentosa and macular degeneration - MIT - 2nd Sight (Alfred Mann Foundation) - Gregg Suaning, U. New South Wales (100 ch. Bidirectional RF-CMOS) n Cochlear prosthesis - Advanced Bionics Corporation n Pacemakers

8. September, 25, 2003The Krasnow Institute Seminar Typical Specifications n Input Impedance: up to 1G ohms, 10pF (e.g. for good voltage xfer from electrodes) n Sensitivity: mV n Channel bandwidth: 100-100kbs, 1Mbs needed n Carrier frequencies: 1-200MHz (contrast with fund. mode crystals up to around 40MHz) n LO Phase Noise: -100dBc/Hz spot noise at 500kHz offset from carrier (contrast with state-of-the-art optical communications: -100dBc/Hz at 100kHz from 2.5GHz approx. 32dB lower!) n Size: 10s of mm side length (contrast with typical IC sizes of 4-30 sq. mm.) n Weight: 1-40g n Inductor sizes: mm (half-wavelength) (motivation for higher carrier frequencies: λ = c / ε r / f ) n RF link operating distance: cm to meters n Power consumption: mW n Power supplies: (set by technology): 3.3V - 1.0V n Temperature Range: Wildlife apps: -20-50 C, Implants: 30-45 C ? n Battery Life: 100s of hrs to several years n Packaging Materials: PECVD silicon dioxide, silicon nitride, DLC, parylene

9. September, 25, 2003The Krasnow Institute Seminar Telemetric Transceiver - Block Diagram Sensor/Preamp n Data Conv. RectifierRegulator MUX Sensor/Preamp 1 Power Inductive Power/Data Link (E.g. sigma-delta modulators) LO (Xtal, SAW, or PLL) Tissue interface Piezoresistive accelerometers SAW resonators Thermistors Pressure sensors Ion concentration sensors Micro-electrode arrays M L ext L int Mod/Dem: PCM, PPM, PSK, etc.

10. September, 25, 2003The Krasnow Institute Seminar Power Reduction Strategies n Devise low power standby modes (turn circuits off when not in use) n Smaller technology & lower power supply voltage n Inductive power coupling (>70% efficiency) n Low-power mod/demod; e.g. PCM n Reduce RF data link operating distance n Magnetically-coupled oscillators (instead of shielding) n Injection-locked frequency division (on the order of 6dB power reduction over brute-force methods)

11. September, 25, 2003The Krasnow Institute Seminar Data Conversion: Modulators l Similar to integrate-and-fire neuron l Very simple to implement l Very high resolution at audio frequencies (up to 20 bits) l Oversampling pushes quantization noise out to high frequencies (noise shaping) l Insensitive to many analog non-idealities + 1/s Sensed analog voltage in Bit stream out 8 5 A.K.A. The Line-Draw Algorithm: How to get from point A to point B in the straightest line on a Manhattan grid: clock 0 - 0 + 5 = 5 (< 8 quiet move over 0) 5 - 0 + 5 = 10 (>=8 fire move up 1) 10 - 8 + 5 = 7 (< 8 quiet move over 0) 7 - 0 + 5 = 12 (>=8 fire move up 1) 12 - 8 + 5 = 9 (>=8 fire move up 1) 9 - 8 + 5 = 6 (< 8 quiet move over 0) 6 - 0 + 5 = 11 (>=8 fire move up 1) 11 - 8 + 5 = 8 (>=8 fire move up 1) 5 pulses out of 8 Example: analog input 5/8 of full-scale:

12. September, 25, 2003The Krasnow Institute Seminar Frequency Synthesis: Multiplying PLL l PLLs drive the phase of an oscillator to be some fixed offset from that of the input. l Ideally, the resonant frequency of the VCO is exactly M times ω i. If not, the VCO is adjusted to the correct frequency by H(s). H(s) + K v /s (φ o φ i ) (ω o Mω i ) V vco =φ o Freq. Divider ( M) V i cos(ω i t+φ i ) V o cos(ω o t+φ o ) (φ e 0) ω f = ω o /M

13. September, 25, 2003The Krasnow Institute Seminar V od cos(ω r t) Voltage-Controlled Oscillator finite Q ω r =1/ LC R loss C L - R loss M1M1 M2M2 M3M3 M4M4 EQUIVALENT TANK CKT: C L RsRs RsRs 1/f 3 1/f 2 ΔfΔf dBc /Hz Phase Noise: LC or ring-oscillator? LC-based VCOs are much less noisy than ring- oscillators power reduction for given noise performance Immunity to EMI: To shield or not to shield? Shielding via low- metal reduces the Q and increases power for given noise performance. Magnetic coupling can de-tune far-field (even-mode) response curve away from near-field (odd-mode). R loss C2C2 L2L2 - R loss R loss C1C1 L1L1 - R loss V1V1 + - V2V2 + - Mutual inductance, M 1/f up-conversion capacitor PHASE NOISE PSD:

14. September, 25, 2003The Krasnow Institute Seminar Half-ckt, small-signal analysis (negative resistance cancels loss in tank) : V od cos(ω r t) V od /2 T-model -V od /2 i 1 =g m1 (V od /2-V s ) Negative Resistance ro1ro1 1/g m1 RsRs i o = (approx i 1 ) ro1ro1 i 1 =G m1 (-V od /2) G m1 = g m1 /(1+ g m1 R s ) SOURCE-DEGENERATED EQUIVALENT CKT: =>R eq =-1/G m1 = -R loss at resonance M1M1 M2M2 M3M3 M4M4 => C L RsRs RsRs VsVs

15. September, 25, 2003The Krasnow Institute Seminar Magnetically Coupled LC VCOs V 1 = - I 1 (sL+1/sC) = MI 2 s Letting L= L 1 = L 2 and C= C 1 = C 2 => ω r = ω r1 = ω r2 M = k sqrt(L 1 L 2 ) = kL V 2 = - I 2 (sL+1/sC) = MI 1 s and solving the following simultaneous equation: yields two steady-state solutions, or modes: V1V1 V2V2 = V2V2 V1V1 = -1 (odd mode, V 1 and V 2 oscillate out of phase) V1V1 V2V2 = V2V2 V1V1 = 1 (even mode, V 1 and V 2 oscillate in phase) ω r2 =1/sqrt(L 2 C 2 ) ω r1 =1/sqrt(L 1 C 1 ) R loss C2C2 L2L2 - R loss R loss C1C1 L1L1 - R loss V1V1 + - V2V2 + - Mutual inductance, M Advantage: Common- mode disturbances at ω o are attenuated! More coupling => more attenuation. ω o = ω r (1+.5M/L) ω e = ω r (1 -.5M/L) Stand-alone res. freqs -> ωrωr ωoωo ωeωe odd mode even mode

16. September, 25, 2003The Krasnow Institute Seminar Injection-Locked Frequency Divider Ideally, ω r =2ω i, but it will not in practice, so we need to pull the oscillator before phase-locking. Non-linearity is used to pull and injection-lock an otherwise free- running oscillator at its natural frequency, ω r : H(s) = sH o ω r /Q s 2 +s ω r /Q + ω r 2 ;Δω r = ω o -ω r (how far the oscillator is currently off the BP resonance) V o cos(ω o t) f(x) + f(x)=a 1 x+ a 2 x 2 V i cos(ω i t + φ) H(ω)=BPF Injection source oscillator ωrωr VfVf HoHo 1+j2QΔω r /ω r Also define: Δω e = ω o - ω i /2 (how far the output freq. is currently from half the input freq.) H(jω) =

17. September, 25, 2003The Krasnow Institute Seminar V o = H(jω o )V f = H o V f 1+j2QΔω r /ω r Output = Input x H(jω o ): ;V f (t)=a 1 V o cos(ω o t) + a 2 V i V o cos((ω o - ω i )t - φ) 1+j2QΔω r /ω r = H o [a 1 + a 2 V i e jφ ] Equating imaginary parts: Using complex exponentials and neglecting Δ ω e : Δω r /ω r =.5H o a 2 V i sin( φ )/ Q The maximum locking range corresponds to when sin( x )=1 => Δω r /ω r < H o a 2 V i /2Q If ω r is perfectly matched to ω i /2 then s.s. phase error is zero. V o cos(ω o t) f(x) + f(x)=a 1 x+ a 2 x 2 V i cos(ω i t + φ) H(ω)=BPF Injection source oscillator ωrωr VfVf Lock Range

18. September, 25, 2003The Krasnow Institute Seminar V i cos(ω i t) V od cos(ω o t+ φ o ) L L C C VsVs Injection-Locked Frequency Divider M1M1 M2M2 M3M3 V od + - ω r =1/sqrt(LC) R loss C L - R loss Small-signal half-ckt: V od /2 ro1ro1 1/g m1 T-model -V od /2 i 1 =g m1 (V od /2-V s ) i 3 =g m3 V i ro3ro3 ioio Using driving-point impedance, inspection, or other analysis technique: i o = - G m1 V od /2 + g m3 r o2 G m1 V i Thus, the output current is a mixture of output frequency and injection source. To see the pulling and injection-locking, we must consider large-signal effects... EQUIVALENT TANK CKT:

19. September, 25, 2003The Krasnow Institute Seminar Consider a pseudo-large-signal half-ckt analysis (i.e. still use small- signal approximation for tail current source, M 3 ): I dsat =[.5μCoxW/L](V GS -V t ) 2 ; V GS = V G - V S = V GS DC + V GS AC IoIo M1M1 M3M3 V I =V I DC + V I AC V G = V G DC + V G AC AC components of V GS : V G AC = -V od /2, V S AC = V I AC g m3 /(g o3 + g m1 ) DCAC (V GS -V t ) 2 = [[V GS DC -V t ]- [V od /2+ V I AC g m3 /(g o3 + g m1 ) ]] Large-signal 2nd-order non-linearity comes from square-law: Thus, the linear mixture of oscillator frequency and injection source is mixed via 2nd-order nonlinearity, producing intermodulation terms near ω r, which is intentionally placed near ω i /2. This energy serves to injection lock the oscillator. Injection-Locked Frequency Divider

20. September, 25, 2003The Krasnow Institute Seminar Summary n Biotelemetry is useful for - Neural stimulation (data in device) - Neural recording (device data out) - Eliminating tethering forces - Vital sign monitoring - Animal tracking n Biotelemetry represents a multidisciplinary research area that enables collaboration and offers a diverse EE design experience: ckt design EM communications sensor design transmission- line/waveguide design antenna design n Todays CMOS technology may be leveraged to reduce power and size, improve performance, and increase throughput References available upon request. THANK YOU!