Making Sense of Wireless Sensor Power Consumption. Steven Lee Application Engineer

Making Sense of Wireless Sensor Power Consumption Steven Lee Application Engineer

Agenda The importance of optimizing power consumption on sensors Test Case: Tire Pressure Monitor Sensor Traditional approach to dynamic current measurements New approach to dynamic measurements Summary

A World Full of Sensors Sensors are present in almost every aspects of daily life Measures/senses everything from humidity to earthquakes It is critical to understand the power consumption of sensors especially as it is integrated into your design 3

Example: Wireless Lock Solutions What is it and what s important: Wireless lock solutions for access control, identification, mobile keys, keyless entry systems Used in hotels, residences, businesses Want to maximize battery run-time Need to evaluate current drain profile to improve design 4

Example: Mobile AMR (Automatic Meter Reader) What is it and what s important: Battery-powered metering to monitor water, gas, electric, leak control Contains battery, RF transmitter, µp, memory Want to improve battery run-time Remotely located AMR s need long battery life (5 to 20 years) 5

Example: Wireless Activity Monitor What is it and what s important: Wireless activity monitor and health monitor Results transmitted to customer s smartphone Want to maximize battery run-time Need to perform battery run-down test over several days Simplifying characterization of Energy Drain 6

Example: Wireless Sensor Nodes What is it and what s important: Wireless sensor applications Earthquake/structure monitors, light and fluid monitors, event monitors, medical and fitness sensors, smart parking, energy, water, tanks, silos, liquid, gas, humidity, temperature, security, safety, logistics, etc. Want to improve battery run-time Remotely located sensors need long battery life (>10 years) 7

Why is Optimizing Battery Run-time So Important Now? Top Concern to Users of Increasingly Capable Sensors Rise of IoT and Smart Home Applications Always-connected Greater % of time being used Complex interaction of applications/software/hardware Larger batteries in use still not enough! Inadequate design and analysis leads to: Shorter device run time Unanticipated periods of high battery drain Additional design cycles Dissatisfied end-users Optimizing battery run-time, in all phases of design, leads to: Longer running, more competitive products Faster time-to-market Less problems in field Delighted end-users

Common Attributes Main components are microcontroller, transceiver, memory, ADC, power management, and power source Power source is typically a single cell battery (or battery pack) Performs a measurement and RF communication Incorporate multiple power savings modes from 100 s of na range (hibernate) to 10 s of ua range (sleep) to 10 s of ma (active/measurement) up to 100 s of ma (transmit) A key design challenge maximizing battery life. R&D design and software engineers need to understand current drain, accurately measure current drain and make HW & SW tradeoffs to minimize power consumption. 9

A Growing Need for Battery Current Drain Testing In Hardware Development, optimize energy efficiency: Evaluate and optimize overall device and its sub circuits for battery drain In Software Development, validate new code builds: Run application code regression test suites, assess impact on battery drain In Design Integration and Validation, run suites of benchmark tests: Validate battery drain for all required operational modes Validate operating time with product s battery (battery run-down test) Benefits: Maximize your device s battery life Multiple methods for viewing and understanding what parameters in your design affect battery life, increasing your confidence in repeatable results Direct comparison of battery drain profiles for each design revision, provides clear documentation for FDA of design changes on battery life 10

Amperes Test Challenge How to accurately measure dynamic current? Range Measurement Accuracy 8 A Activity 100 ma Idle 1 ma Sleep 11

What is a TPMS Device? 13

TPMS Diagnostic Tool What does this tool do? Menu scroll Initiate a sensor reading On/Off (Press & Hold) 14

TPMS current drain values 15

Examining Details of Idle Current Waveform 16

Examining Details of TPMS Idle Current Activity 1.4 ma pulses every 30 seconds 17

Examining Details of Idle Current Activity 1. Position markers over small pulses 41 ua pulses every 2 seconds 18

Examine Details of TPMS Transmit Burst Current Drain 14585B 2.3 sec pulse train Average Current 894 ua Peak Current: 7.4 ma 19

Insight Why is this measurement challenging? Very low level idle current with large pulsed activity Unable to see the details using scope Unable to data log using a scope DMM range changing causes issues 20

Battery Drain Test and Analysis for Simulated Real-world Use Traditional Solution: Custom RF Stimulus & Current Drain Logging Setup Challenges: Properly powering DUT Making accurate, high resolution measurements Generating combinations of DUT activities and simulating wireless network Processing and managing massive amounts of data Effective tools for visualizing and analyzing results Development effort, resources and time

Traditional Measurement Solutions for Battery Drain Test DC source or battery + - + Shunt + DUT current - - Data acquisition equipment Diff Amp MUX Gain Amp PC to log long-term data ADC DUT Data out Most common: Shunt + DAQ equipment Typical performance: ~14 to16 bits ~ 200K to 1M samples/sec ~ 0.2 to 1.0% gain error (both shunt and DAQ) ~ 0.02 to 0.1% of full scale offset error (mainly DAQ) Commonly encountered issues: Peak voltage drop on shunt may be excessive Transient voltage drop at DUT when using a general purpose DC source can be excessive Large effort to configure and program Fixed offset error is 40 to 200 times greater than target of 0.0005% The fixed offset error of most traditional test equipment limits their performance measuring battery current drain signals 23

Test Challenge: Measuring Current Accurately Scope Ammeter V meas shunt shunt V bat V burden V DUT DUT V burden DUT I bat V bat I bat V DUT Scopes V DUT = V bat V burden Good bandwidth for dynamic current Advanced triggering Time correlation with digital bus Excellent update rate Limited vertical accuracy Selecting proper shunt is nearly impossible to get good low current measurement and tolerable burden voltage at high current No long term measurements DMMs/Ammeters: V DUT = V bat V burden Sufficient accuracy Insufficient bandwidth for dynamic current Imposes an unacceptable burden voltage 24

Keysight Solution solves measurement problem Very Challenging measurement using traditional test tools (wide dynamic range tough to measure) Detailed Current Measurements provide key insights to operations and their efficiency Seamless Measurement ranging provides accurate results over full operating range (sub ua up to Amps) Gapless data logging provide continuous current drain measurement No external equipment needed Provides key insights to idle and transmit operation, it s efficiency, and acceptable query rate Greater insights through innovative measurements 26

Innovation for Accurate Current Drain Measurements N6705 DC Power Analyzer Mainframe Integrates multiple instrument functions into a single box: 1 to 4 advanced power supplies; > 30 different models available Digital voltmeter and ammeter Arbitrary waveform generator Oscilloscope Long term data logger Output Sequencing Full functionality from front panel Gain insights in minutes, not days! N6785A 2-Quadrant SMU for Dynamic Current Drain Analysis Specialized DC power supply module for current drain testing: Up to 200 ksa/s digitizing rate Fast transient response for pulsed loads Settable battery emulation characteristics Auxiliary DVM input port for battery run-down testing Innovation: Seamless Measurement Ranging for accurate measurement of battery drain spanning wide dynamic ranges 27

Usability Enhanced via Emulation Modes To simplify use, each SMU has user-selectable emulation modes Keeps operation in quadrant and optimizes features and settings for the application V V V I I I 4-Quadrant Power Supply (N6784A) V 2-Quadrant Power Supply Battery Emulator w/prog R (N6785A) Unipolar/1-Quadrant Power Supply Battery Charger (N6785A) Constant-Current (CC) or Constant-Voltage (CV) Electronic Load I V Voltage Measure (Voltmeter) A Current Measure (Ammeter) 28

N6785A/86A Sourcing Capability Load -4A 20V +4A Source -5A 15V +5A -6.7A 10V +6.7A -8A 6V +8A

Keysight N6785A Seamless Current Ranging Innovation Performance Range 8 A 100 ma 1 ma Measurement Accuracy Current ±(0.04% + 1.5mA) ±(0.025% + 10µA) ±(0.025% + 100 na) Seamless measurement between these 3 ranges Seamless ranging continually changes ranges without glitch nor lose readings 200 khz, 18-bit digitizer, with seamless ranging, acts likes single range of ~30-bits 8 A range with an effective offset error as low as 110 na (0.01 PPM) Measure ranges are independent from source ranges and don t impact the output voltage stability. Accurate measurements from Amps to sub-µa during a single scope sweep or data-log 30

Seamless Range Changes Amperes Seamless Dynamic Current Measurement Accuracy and Speed with no wasted time during current ranging Range Measurement Accuracy = Seamless range change 8 A ±(0.04% + 1.5mA) Transmit 100 ma ±(0.025% + 10 A) Measure 1 ma ±(0.025% + 110 na) Sleep 200 ksa/s, 18-bits digitizers acts likes single range of ~30-bits 31

Seamless Current Measurement All new, Keysight-exclusive feature never been done before Can change range, without glitch, mid-sweep and not lose any readings 200 khz, 18-bit digitizer acts likes single range of ~28-bits Allows for accurate measurements from Amps to µa during a single scope sweep or data log (1,000,000:1) Yesterday Today Seamless Off Seamless On See the complete current waveform you ve never seen before from na to A in one pass and one picture 32

Item N6781A Battery Drain Analyzer SMU N6782A Functional Test SMU N6785A Hi Power Battery Drain Analyzer SMU N6786A Hi Power Functional Test SMU Size 1 slot wide 2 slots wide Power 20 Watts 80 Watts Voltage source ranges Current source ranges Measurements 20V at up to +/-1A = 20 W 6V at up to +/- 3A = 18 W 600 mv at up to +/- 3A = 1.8 W +/- 3A at up to 6V +/- 1A at up to 20V +/- 300 ma at up to 20V 3 voltage measurement ranges Seamless ranging down to 1 ma FS range with (100 na max offset error) 10 µa FS range (Fixed range) 20V at up to +/- 4A = 80 W 15V at up to +/- 5A = 75 W 10V at up to +/- 6.7A = 67 W 6V at up to +/- 8A = 48 W +/- 8A at up to 6V +/- 6.7A at up to 10V +/- 5A at up to 15V +/- 4A at up to 20V One voltage measurement range (0-20V) Seamless ranging down to 1 ma FS range with (100 na max offset error) 10 µa FS range not available

100 ma N678x Series SMU Modules Measurement Challenge: Long Term Datalog - Gapless na na na na na na na 2s / div 34

Measure Only Modes Voltmeter and Ammeter Allows just the measurement features to operate, without sourcing power into the DUT Allows the module to be used as a general purpose measurement instrument for any signal, not just the voltage or current that the module is sourcing Can measure either voltage or current or both When measuring current, you can also configure the module to make current measurements without any burden voltage You can use the Auxiliary DVM to measure voltage Measurements can be Integrated, single measurements (like a DMM) An array of digitized measurements (like a scope) Many measurements taken over time (like a data logger) 35

Current Drain with Virtual Ammeter Whole device and Sub-circuit Device Battery + + Battery Current Drain 0 Volts Ammeter + _ DUT N6785A Aux In Voltage Measurement Identify where current is used with subcircuit measurements: Multiple channels can be measured with simultaneous sampling and time correlated on Scope or Datalogger screen 36

14585B Control and Analysis Software Compliments N6705C front panel by controlling instrument through PC application Familiar PC user interface Extends N6705C features Waveform generation (more canned waveforms, import waveforms from previously captured measurements, create waveforms using equation) Scope and Data Logger (larger display, more traces) Adds new capabilities Data log direct to disk Record waveform and then playback Battery drain analysis (battery rundown test, statistical analysis/ccdf) 37

Complementary Cumulative Distribution Function Increase % time Display Result Decrease % time Display Result Decrease peak current Increase peak current The CCDF function is very useful to determine how much current was drawn during a specific percentage of one s datalog record 38

Agenda 2015 Keysight Technologies The importance of optimizing power consumption on sensors Test Case: Tire Pressure Monitor Sensor Traditional approach to dynamic current measurements New approach to dynamic measurements Summary

Summary Battery drain end user achievements Battery powered sensors are an integral part of everyday life. They are everywhere! Designers must find an effective measurement technique to capture and analyze the power consumption in their sensors Traditional measurement techniques fall short of capturing the dynamic current characteristics Keysight provides a one box solution in analyzing the power consumption of sensors through the N6705 DC Power Analyzer, N6785A Source Measure Unit, and 14585B companion software 40

Thank you! 41