Ultra-Low-Power Circuits for Wearables

Public Information

Ultra-Low-Power Circuits for Wearables

Philippe Bourban

30.11.2016

Public Information 2 11/30/2016

Outline

• ON Semiconductor quick facts

• Power budget of some wearable devices

• Things to think about to make ULP circuits

• A few circuit examples

3 Public Information

• Headquarters: Phoenix, AZ

• Employees: ~30,000 globally

• Revenue: ~$5Bn(1)

• Market Capitalization: ~$4.9Bn(2)

• Ticker: ON

• Founded: Spun-off from Motorola 1999, IPO 2000

(1) Estimated Fiscal 2017 Revenue per Factset 11/8/2016; (2) As of October 24, 2016; Sector % based on 3Q16

ON Semiconductor Today

4 Public Information

Proven Leadership Growth Drivers

Industrial ASIC #1

Notebook Adapters (ACDC) #1

Adaptive Front Lighting #1

Automotive Image Sensors #1

Linear VREG #1

Security Image Sensors #1

Audiology DSP Systems #1

PC Core Power (DCDC) #1

White Goods IPM #2

Protection #1

GP Op Amps #2

Automotive

Sources: iSuppli, IMS Research, Strategy Analytics, Fuji Chimera Research, ON Semiconductor Business Units and Corporate Marketing

Power Conversion & Motor Control

Image Sensors

Industrial IoT Wireless Devices


Typical elements in wearable devices

Sensor(s)

Data

acquisition

chain(s)

Data

processing

Wireless

connectivity

• Signal conditioning

(amplify, filter…)

• A/D conversion

• μC

• DSP

• ASIP

• Dedicated HW

• NFC

• RFID

• Bluetooth Classic

• Bluetooth Low-Energy

• ANT

• Wifi

Power management unit

Driver Actuator /

Display

• Accelerometer

• Gyroscope

• Magnetometer

• Altimeter

• Barometric pressure

• Heart rate

• ECG

• Oximetry

• Respiration

• Infrared

• Skin conductance

• Skin temperature

• Ambient temperature

• Ambient light

• UV


Power budget of some wearables (1) AR glasses Sportswatch Fitness tracker Fitness tracker

Recon Instruments Snow2 HUD Samsung Gear S2 Tomtom Spark Cardio+Music Garmin Vivosmart HR+

1200 mAh @ 3.7V 250 mAh @ 3.8V 230 mAh @ 3.8V 80 mAh @ 3.8V

6 hours 36 hours (display on)

72 hours (display off)

5 /11 hours (music/GPS)

3 weeks (activity tracking)

8 hours (use)

120 hours (standby)

740 mW 26 mW (display on)

13 mW (display off)

175/80 mW (music/GPS)

1.7 mW (activity tracking)

38 mW (use)

2.5 mW (standby)

• Wifi, BT, GPS

• 9-axis accel. & gyroscope

• Compass sensor

• Pressure sensor

• Temperature sensor

• 0.2” TFT-AMLCD display

• Wifi, BLE, NFC

• 6-axis accel. & gyroscope

• Heart Rate sensor

• Pressure sensor

• Ambient light sensor

• 1.2” Super Amoled display

• GPS, BT

• 6-axis accel & gyroscope

• Heart Rate monitor

• Bio-sensor

• 3-axis magnetometer

• 1.3” LCD display

• GPS, BLE, ANT

• 3-axis accelerometer

• Heart Rate sensor

• Pressure sensor

• 1.6” TFT-LCD display

• 1 GHz dual-core OMAP4430

• Graphics processor

• 1 GHz dual-core Exynos

3250

• ARM Cortex M7

• Atmel 8-bit MCU

• 120 MHz ARM Cortex M4

Data from www.techinsights.com


Power budget of some wearables (2) Bluetooth earbuds Bluetooth earbuds Bluetooth earbuds Hearing Aid

Bragi Dash Earin

Motorola moto hint 89765N

100 mAh @ 3.7V 60 mAh @ 3.7V 120 mA @ 3.7V 160 mAh @ 1.2V

(disposable)

4 hours 3 hours 10 hours 100 hours

92 mW 74 mW 44 mW 2 mW

• BT audio streaming

• 3-axis accelerometer

• Gyropscope

• Magnetometer

• Dual pulse oxymeter

sensor

• BT audio streaming • BT audio streaming • Audio processing

• Audio streaming


A few power consumption numbers

Circuit Power consumption

BLE radio 10 mW (peak)

GPS 70 mW

Wifi 240 mW

ARM Cortex M3 0.1 mW/MHz

Exynos 7420 0.25 mW/MHz (14nm FinFET)

12-bit ADC @ 1 Msps 0.2 mW

3-axis digital accelerometer 3 mW (peak)

1 to 30 uW (average @ 1 Hz)


System

Software / algorithm

Architecture

Circuit

How to make ULP circuits?

Technology

• Main power contributors?

• HW/SW partitioning

• Power-down

• Complexity

• Concurrency

• Regularity

• Processor architecture

• Analog vs digital

• Parallelism/Pipelining/Encoding

Digital:

• Voltage reduction

• Activity reduction

• Power gating

• State retention

• Flavors (LP, etc…)

• Multi-threshold devices

• FDSOI / DDC / back-biasing

Analog:

• Weak inversion

• Transistor sizing

High

Low

Typ

ica

l P

ow

er

Sa

vin

g


Analog

Digital

Radio

Audio streaming

Analog

Digital

Radio

Consumer monitoring

Analog

Digital

Radio

Medical implantable

Understand the power breakdown

• Sleep 96% of the time

• Wake up every 100 ms

to send 20 bytes

• Dynamic power is

dominant

• Avg power: 50 mW

• Sleep 99.9% of the time

• Wake up every 10 s to

send 20 bytes

• Memory leakage power

is dominant

• Avg power: 1.5 mW

• Radio active 7.6% of the

time

• Receive data @ 48 kbps,

10 ms frames

• Dynamic power dominant

(audio decompression)

• Avg power: 1.5 mW


Select the right processor architecture

Dedicated

Hardware

DSP

ASIP

General

Purpose

Processor

Energy

Efficiency

Flexibility


• Pdyn = a* f * C * Vdd^2

• Pstat = Ioff * Vdd

Reduce the supply voltage: yes but…

• Trade-off power versus performance (operating frequency)

• Process variability at low voltage Vt mismatch FD-SOI, DDC


Cost • Development

• Production

Which process technology?

Today’s popular choices for a wearable SoC Low-cost : 180 nm

Mainstream : 65 nm / 55 nm

Advanced : 40 nm / 28 nm

Performance • Analog (noise)

• Computing

Power • Static

• Dynamic

Flash

availability

Die area

Memory needs

RF technology System

partitioning

Technology

selection


ULP circuit examples


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1.E-06 1.E-04 1.E-02 1.E+00 1.E+02

Effi

cie

ncy

[%

]

Load Current [mA]

Buck efficiency vs load (mA) @ Vout=1.2V

Vin=3.3V

Vin=1.8V

Efficient DC-DC converter

LTC3549 (high efficiency buck converter) ON Semiconductor

High efficiency step-down conversion at low load currents (100 nA to 100 mA) is important

for ULP circuits or for use cases where the system is often idle (e.g. vital signs sensing)

Buck efficiency vs load (mA) @ Vout = 1.5V

42% @ 100 mA load

85% @ 1 mA load


ADC energy efficiency

PCM4220 (TI)

MAX98091 (Maxim)

WM8786 (Wolfson)

AD1974 (AD)

ISL26102 (Intersil)

LTC2440 (Linear)

TLV320 (TI)

State-of-the-art in 2013


ADC energy efficiency

ON – 2007

(audio)

ON – 2010

(ECG)

ON – 2014

(audio)

ON – 2002

(monitoring)

PCM4220 (TI)

MAX98091 (Maxim)

WM8786 (Wolfson)

AD1974 (AD)

ISL26102 (Intersil)

LTC2440 (Linear)

TLV320 (TI)

State-of-the-art in 2013


• More sensors

• More wireless, with multi-standard radios

• Lower power consumption of individual

functions

• Smaller technology nodes (40nm & 28 nm)

• SoC integration (AFE + mC + radio)

• Security

Trends in wearables


• ULP circuits are at the heart of wearables

• Low-power is in the DNA of local companies

due to the watch industry heritage

• Neuchâtel and Western Switzerland are well

equipped to solve most low-power

challenges in wearables devices

Conclusion


Questions?

Ultra-Low-Power Circuits for Wearables

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