Next Generation Biometric Sensing in Wearable Devices

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1 Next Generation Biometric Sensing in Wearable Devices C O L I N T O M P K I N S D I R E C T O R O F A P P L I C AT I O N S E N G I N E E R I N G S I L I C O N L A B S C O L I N.T O M P K I N S I L A B S. C O M

2 Wearables & 3 rd Wave of Computing DESKTOP COMPUTERS LAPTOPS TABLETS HANDSETS INTERNET OF THINGS CONNECTED HOME SMART CITIES WEARABLES

3 Next Generation Wearable Sensing MOTION ENVIRONMENT BIOMETRICS Today s Wearables Accelerometer Magnetometer GPS Ambient Light Heart Rate Next Gen Wearables Gyroscope/ Accelerometer+ Barometer UV Index Temperature Heart Rate++ Skin Temp Other Biometrics Other Biometrics include SpO2, Stress, Recovery, Hydration High Performance optical sensing, EDA and ECG sensing

4 Next Gen Motion Sensing Next generation motion sensing Repetition counting Exercise identification Form and technique Coaching and guidance

5 Next Gen Environmental Sensing Barometer Combined with motion or GPS location tracking Ambient Temperature Sensing and Skin Temperature Sensing Difficult to implement UV Index Sensing Recommend diffusor & cumulative UV exposure sensing UV transparent overlay

6 Photoplethysmography Basics LED to Photodiode ~1.5 to 5 mm Green LED Light is modulated by the blood flow causing capillary diameter changes The green light is greatly attenuated by tissue Green light works well Red and IR works for finger tip but not at wrist Subdermal Tissue 100 us pulses repeated at 25 Hz Skin Green LED Sensor PD Attenuated and Modulated light Optical Blocking is critical

7 Photoplethysmography Examples Stationary Subject Modulation is 0.5% RMS in this case Very Clear, Low noise heart rate Signal ~75 BPM Modulation HR Period Exercising Subject Many motion artifacts Needs special software and accelerometer signal to extract HR signal Sample # (100 Hz) Sample # (100 Hz)

8 Heart Rate Sensor System Design Optical hardware design Photodiode to LED spacing Overlay Modules solve many system challenges Discrete PD + 2 LED s ~5.06 x 4.26 mm HRM Module 3.7 x 7.0 x 1.1 mm SKIN Glass Overlay Lens Photodiode Clear Encapsulant Substrate Blocking Plastic Clear Encapsulant Lens LED

9 Improved PPG Overlay and Fit Blocking Overlay Highest performance due to zero crosstalk Minimize overlay thickness Minimize module to overlay distance Band and fit considerations Sensor protrusion Fit and secure band

10 SNR [db] High Performance PPG Design Optical Sensor ADC SNR Integration Time [μs] RAM & MCU memory and MIPS Clock stability target <1% More important with FIFO/sample buffer Avoids high MCU power for synchronizing Synchronization between sensors Accelerometer interface supports data synchronization Higher performance optical sensors Multiple LED s, spacing from sensor to LED to make power/performance tradeoffs Noise mitigation becomes more critical: ambient light cancellation and motion artifact cancellation

11 System Power Considerations Power HRM Signal Capture Signal Processing Wireless Transaction Sleep Techniques to extend battery life High performance sensor system + good optical design enables more signal for less light/power Shorter LED duration, integration time while maintaining high SNR results at lower power Sample buffer reduces CPU bus transaction times Wireless radio update interval as long as practical Time

12 PPG+ Enables New Biometrics Heart Rate Variability (HRV) Hydration SpO2 Recovery rate Sleep Quality P u l s e O x i m e t r y

13 ECG & Bio-impedance Electrocardiogram (ECG) Sensing heart s electrical signals Chest strap most common tool for this today Used for heartbeat waveform analysis Bio-Impedance or tissue impedance sensing Most common method to analyze body fat Can be used for hydration measurements Alternate method of sensing heart rate

14 Heart Rate Measurement Algorithm Considerations Motion cadence may equal heart rate Algorithm uses multiple factors to determine HR Algorithm affects accuracy of biometrics & dictates power consumption of HRM system

15 Biometric Performance Optimization Tradeoffs for performance versus power consumption and cost of solution Market segments have different requirements Factors affecting performance Sensor/photodetector selection, optical design LED current dominates power consumption Algorithm performance variations and tuning vs particular activity Automatic motion detection as input to HRM algorithm Reducing noise critical to performance Band design very important to reduce motion noise Ambient light noise Accelerometer to cancel motion noise

16 Next Gen Wearable Wearable 3.0 Motion Tracking Guidance and Coaching Accurate Heart Rate Monitoring Accurate Calorie Estimate Stress Hydration Training effect & fitness Level UV Index & Comfort Level

17 Time for Questions