Carlo Canziani Business Development EMEA Agilent Technologies

Transcription

1 Ottimizzare il tempo di operatività delle batterie nei dispositivi wireless New Innovation Dramatically Improves Battery Current Drain Measurement Accuracy Carlo Canziani Business Development EMEA 1

2 Wireless Revolution = lot s of mobile battery powered devices 2

3 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: Bring smaller, longer running, more competitive products to market Faster time-to-market and at lower expense by reducing development time 3

4 Battery Drain Characteristics for Power Savings Operation 14 s/div 3 ma/div 500 ms/div 50 ma/div Wireless Temperature-Humidity Sensor GPRS Smart Phone Battery Drain for Standby Wireless devices operate in short bursts of activity to conserve power: Applicable to a very wide variety of devices (handsets, environmental sensors, Bluetooth devices, etc.) Long periods of sleep between bursts of activity Resulting battery current drain is pulsed; extremely high peak, low duty cycle, and low average values challenging to measure accurately! 4

5 Detailed Battery Drain Measurements Yields DUT Insights 3 ma/div 91 ms/div 14 s/div 3 ma/div Wireless Temperature-Humidity Sensor 38 sec-long, 7.54 µa sleep periods Dual Transmit Burst 1-temp, 1-humidity 0.19 sec-long each 8.6 ma average during burst 3 ma/div 11 ms/div 99% of the time is sleep; 7.46 µa average (7.54 µa * 99%) 1% of the time is transmit; 86 µa average (8.6 ma * 1%) 12,900 Hrs (1.5 yrs) with 1.2A-Hr battery (93.5 µa total drain) Transmit Burst Pulses 14.4 ma pulse plateau 2.01 ma idle current 5

6 Mobile Phone Discontinuous Receive (DRx) Extends Standby Receive current pulses 50 ma/div 500 ms/div Sleep current base GPRS Smart Phone Battery Drain for Standby 1.22 ma sleep current during 1.25 s paging interval Long periods of sleep conserve power between receive bursts 98.1% of the time is sleep; 1.2 ma average contribution (1.22 ma * 98.2%) Short bursts of receive activity check for incoming pages (see above) 1.8% of the time is Rx; 1.69 ma average contribution (92 ma * 1.8%) 50 ma/div 5 ms/div Current pulse details resulting from Receive (Rx) Burst 23 ms long pulse 239 ma peak current 92 ma average current over burst Resultant standby time is 346 hours for a 1 A-hr battery (2.89 ma total) but we need to consider any transceive activity first 6

7 Mobile Phone Standby Mode; Intermittent Transceive Activity Transmit current pulses Receive current pulses 500 ma/div 2 ms/div idle current GPRS Smart Phone Battery Drain for Transceive In standby mode, a mobile phone can transceive up to several times an hour: Transceives for 10 s to 100 s of ms periods (lets base station know its still there, etc.) Overall average transceive activity is minimal (for this example 720 ms / 1 hr = 0.02%) Resulting battery drain due to transceive is pulsed; for GSM/GPRS example above: 0.58 ms, 2.02A and 143 ma TX and RX pulses, every 4.6 ms frame Average current is 300 ma but overall average contribution is just 0.06 ma (0.02% * 300 ma) Impact on standby time is minimal. Bigger issue is measuring >2 A peak current! 7

8 Mobile Phone Battery Drain Testing; Measurement Needs In summary: A mobile phone standby current drain spans a wide dynamic range reflecting a composite of a wide range of activities: Sleep activity: ~100 µa to ma level (lowest) Idle activity: ~20 to 50 ma level Receive activity: ~100 to 300 ma pulses Transmit activity: ~1 to 2.5 A pulses (highest) Overall standby average battery drain: ~ 0.5 to 5 ma Standby activities vary over time (~ hour timeframe) Dictates having a 2.5 A measurement range ideally with: ~50 µa offset accuracy (0.0001% or 10 PPM) = 10% error for 0.5 ma signal! Able to log current drain at a high rate for an hour or more GSM Association document TS-09 Battery Life Measurement Technique, standby test procedure details: 0.1 ma (100 µa) measurement resolution 50 Ksample/sec logging rate 30 minute logging period 8

9 Traditional Measurement Solutions for Battery Drain Test Most common: Shunt + DAQ equipment DC source or battery + Shunt + DUT current - - DUT 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% offset error (mainly DAQ) + - Data Acquisition Equipment Diff Amp MUX Gain Amp PC to log long-term data ADC Data out Commonly Encountered Issues: Peak voltage drop on shunt may be excessive Transient voltage drop at DUT when using a GP DC source can be excessive Large effort to configure and program Fixed offset error is 200 to 1,000 times greater than target of % The fixed offset error of most traditional test equipment limits their performance measuring battery current drain signals 9

10 New Innovation for Accurate Battery Drain Measurements N6705 DC Power Analyzer Mainframe Integrates multiple instrument functions into a single box: 1 to 4 advanced power supplies; >34 different models available Digital voltmeter and ammeter Arbitrary waveform generator Oscilloscope Long term data logger Full functionality from front panel Gain insights in minutes, not days! N6781A 2-Quadrant SMU for Battery Drain Analysis Specialized DC power supply module for battery drain testing: For use in the N6705 mainframe Settable battery emulation characteristics Fast transient response for pulsed loads Auxiliary DVM input port for battery run-down testing Up to 200 KSa/sec digitizing rate Innovation: Seamless Measurement Ranging for accurate measurement of battery drain spanning wide dynamic ranges 10

11 N6781A SMU Measurement Ranging Performance Measuring DRX Standby Current Drain below for this example Range 3 A 100 ma 1 ma 10 µa Measurement Accuracy Receive current pulses (up to 291 ma) 50 ma/div 500 ms/div Sleep current base (1.22 ma) ±(0.03% µa) ±(0.025% + 10µA) ±(0.025% na) ±(0.025% + 8 na) Seamless measurement between these 3 ranges High digitizing rate, resolution, and DC accuracy are needed for standby operation 1.22 ma sleep base current Peak pulses up to 291 ma, complex shape Low average current of 2.97 ma, determines standby battery life High crest factor makes accurate measurement difficult N6781A seamless measurement ranging greatly extends dynamic range of accurate measurement, spanning to up to 7 decades Improvement depends on signal, shown Parameter Fixed Range Seamless Improvement Overall DC accuracy (2.97 ma avg) 8.5% 0.4% 21 X Sleep base current DC accuracy (1.22 ma avg) 20.5% 0.8% 25.6 X 11

12 N6781A Measure Only Mode: Zero Burden Ammeter for Battery Run-down Using actual battery gives most realistic assessment of DUT performance N6781A regulates zero volts at output while measuring current, acting as a zero burden ammeter, eliminating voltage drop problem of using a shunt N6781A Aux DVM input simultaneously measures battery voltage Application note EN provides details on setting up DUT battery + _ + _ V out - _ Battery current drain 0 Volts Zero burden ammeter A Aux in voltage measurement V out + + N6781A source/measure unit + _ DUT 12

13 Trigger Current Drain Sub Circuits measurements and external triggering DUT + V 1 Sub-circuit 1 Mixed Signal Oscilloscope serial bus DUT current - PMU V 2 V n... Sub-circuit 2 Sub-circuit n N.C. V out + V out - V out - V out + 0 Volts Agilent N6705B Aux in DVM Battery emulator N6781A SMU #1 Aux in DVM A Zero burden ammeter N6781A SMU #2 N6705B DC power analyzer mainframe 13

14 Battery Run-down Test Example Results and Insights Voltage Current Power 24 min/div N6781A SMU and 14585A Software Measuring Battery Run-down on a GSM/GPRS Mobile Phone Results Logged min, avg & max volts, amps, & watts Markers at start and shutdown determine: Insights: I avg = 233 ma V avg voltage = 3.82 V Charge = 843 ma-h Energy = 3.19 W-h Run time = 3 hr 38 min V shutdown = 3.44 V Delivered charge (843 ma-h) less than spec d (1000 ma-h) V shutdown high (target 3V) Often energy (unspec d) is more related to actual runtime than Charge (spec d) 14

15 Using CCDF Profiles to Analyze Improvements in Power Savings, Standby Current Drain Analysis Example 2.4 ma 14.3 ma Discontinuous RX 3.0% 0.16% Continuous RX Comparing CCDF profiles of standby current drain: continuous RX vs. discontinuous RX A (vertical) change of 2.8% of RX activity at 128 ma contributed 18% of the power savings A (horizontal) change of 11.9 ma of the idle current activity (~ 90%) contributed 55% of the power savings The remainder of the power savings is from reduced baseband activity The more random the signal is the more helpful it is to have alternate ways to analyze results 15

16 Summary: A Growing Need for Real World Tests In Development, optimize battery operating time: Evaluate and optimize overall device and its sub circuits Validate and optimize battery power management system Identify high peak drain anomalies and their root causes In Design Integration and Validation: run suites of benchmark tests: Current drain for channels & power level combinations, & main op modes Validate operating time with product s battery (run-down test) Check impact of HW, L1/L2/L3, OS & application interactions on battery drain In Software Development, validate new code builds: Run application code regression test suites, impact on battery drain Benefits: Bring smaller, longer running, more competitive products to market Faster time-to-market and at lower expense by reducing development time 16

17 10 Tips to Optimize a Mobile Device s Battery Life

18 Questions Save the Planet One Battery at Time Carlo Canziani Advanced Power Applications EMEA Business Development Manager Thank you! 18