TIAFE4300低成本衡器和人体成份测量模拟前端解决方案.docx

TIAFE4300低成本衡器和人体成份测量模拟前端解决方案.docx

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TIAFE4300低成本衡器和人体成份测量模拟前端解决方案

TIAFE4300低成本衡器和人体成份测量模拟前端解决方案

关键字：

工业控制,测试测量;医疗电子,人体成本测量

TI公司的AFE4300是低成本的衡器和人体成份（BCM）测量模拟前端（AFE）,集成了两个单独的信号链:

一个用来重量测量,一个采用16位860SPSADC进行人体成份分析.器件中的三个BCM通路允许对身体手和足间的部分身体阻抗进行分析（BIA）,从而得出人体成份的全图.器件的工作电压2V-3.6V,主要用于衡器和人体成份测量.本文介绍了AFE4300主要特性,方框图,衡器前端框图和BCM前端框图以及评估板AFE4300EVM-PDK框图,电路图,材料清单和PCB元件布局图,并介绍了典型的人体成份分析图.

TIintroducestheindustry’sfirstfullyintegratedanalogfrontendforbothweightandbodycompositionmeasurement（BCM）.TheAFE4300isaneasy-to-use,precision,low-powerfrontendsolution,whichallowsengineersdesigningweighscalesthatincorporatebodycompositionmeters,bodyimpedanceanalyzers,andimpedancemeasurementequipmenttogettheirproductstomarketfasterthanbyimplementingexisting,morecomplexmulti-chipsolutions.

TheAFE4300incorporatestwoseparatesignalchains,onetargetingweightmeasurementandtheothertargetingbodycompositionanalysis,witha16-bit,860-spsanalog-to-digitalconverter（ADC）multiplexedbetweenthem.Thedevice’sthreeBCMchannelsenablesegmentalbodyimpedanceanalysis（BIA）betweenbodyextremities,whichallowsforafullpictureofthesubject’sbodycomposition.

TheAFE4300isalow-costanalogfront-endincorporatingtwoseparatesignalchains:

onechainforweight-scale（WS）measurementandtheotherfor bodycompositionmeasurement（BCM）analysis.A16-bit,860-SPSanalog-to-digitalconverter（ADC）is multiplexedbetweenbothchains.Theweight measurementchainincludesaninstrumentationamplifier（INA）withthegainsetbyanexternal resistor,followedbya6-bitdigital-to-analogconverter（DAC）foroffsetcorrection,andacircuittodrivethe externalbridge/loadcellwithafixed1.7Vforratiometricmeasurements.

TheAFE4300canalsomeasurebodycompositionbyapplyingasinusoidalcurrentintothebody.Thesinusoidalcurrentisgeneratedwithaninternalpatterngeneratoranda6-bit,1-MSPSDAC.Avoltage-to-currentconverterappliesthissinusoidal currentintothebody,betweentwoterminals.The voltagecreatedacrossthesetwoterminalsasaresultoftheimpedanceofthebodyismeasuredback withadifferentialamplifier,rectified,anditsamplitudeisextractedandmeasuredbythe16-bitADC.

TheAFE4300operatesfrom2Vto3.6V,isspecifiedfrom0℃to+70℃,andisavailableinaTQFP-80package.

AFE4300主要特性:

•Weight-ScaleFront-End:

–SupportsuptoFourLoadCellInputs

–On-ChipLoadCell1.7-VExcitationVoltageforRatiometricMeasurement 

–68-nVrmsInput-ReferredNoise（0.1Hzto2Hz）

–Best-FitLinearity:

0.01%ofFull-Scale 

–Weight-ScaleMeasurement:

540μA 

•BodyCompositionFront-End:

.

–SupportsUpToThreeTetra-PolarComplexImpedanceMeasurements 

–6-Bit,1-MSPSSine-WaveGenerationDigital-to-AnalogConverter（DAC） 

–375-μArms,±20%ExcitationSource 

–DynamicRange:

0Ωto2.8kΩ 

–0.1-ΩMeasurementRMSNoisein2-HzBW 

–BodyCompositionmeasurement:

970μA 

•Analog-to_DigitalConverter（ADC）:

–16Bits,860SPS 

–Supplycurrent:

110μA

AFE4300应用:

•WeightScaleswithBodyCompositionMeasurements

图1.AFE4300功能框图

图2.AFE4300方框图

图3.AFE4300衡器前端框图

图4.AFE4300AC整流器模式的人体成分测量仪（BCM）前端框图

评估板AFE4300EVM-PDK

AFE4300EVM-PDKisaplatformforevaluatingtheAFE4300device.AFE4300isalowcostAnalog-Front-Endincorporatingtwoseparatesignalchains,onetargetingweightmeasurementandtheothertargetingbodycompositionanalysis.TheEVMprovidesaccessforloadcellterminalstosupportuptofourloadcellinputsforweighscalemeasurements,BCMterminalstosupportuptothreetetra-polarcompleximpedancemeasurements.UserscanalsofeedanytypeofsingleendedordifferentialsignalsdirectlytotheAFE4300throughtheauxiliary（AUX1andAUX2）inputs.Externalsupportcircuitssuchasanti-aliasingnetworkforloadcellterminals,trim-potforsettingthegainoftheInstrumentationAmplifierattheWeighScaleFront-end,InstrumentationamplifiersfortheBCMdifferentialterminals,loadcellsimulationblock,impedancesimulationblock,clocksandexternalreferencesareprovidedfortestingpurposes.

TheevaluationmodulecomeswithaLabVIEW-basedgraphicaluserinterfacethatallowstheusertoeasilyconfigurethedevicetocapturedataandperformanalysisonthedata.NotethattheAFE4300EVM-PDKisintendedforprototypingandevaluationpurposesonlyandisnotintendedtobeusedwithrealsubjectsorpatients.

评估板AFE4300EVM-PDK主要特性:

Supportforuptofourloadcellinputs

Supportforthreetetra-polarimpedancemeasurements

On-boardloadcellsimulationblock

Acquiredataatupto860samples/secondindatacapturemode

USBbasedpowerandPCapplicationconnectivity

图5.评估板AFE4300EVM-PDK外形图

图6.评估板AFE4300EVM-PDK框图

图7.评估板AFE4300EVM-PDK电路图

（1）

图8.评估板AFE4300EVM-PDK电路图

（2）

图9.评估板AFE4300EVM-PDK电路图（3）

图10.评估板AFE4300EVM-PDK电路图（4）

图11.评估板AFE4300EVM-PDK电路图（5）

图12.评估板AFE4300EVM-PDK电路图（6）

评估板AFE4300EVM-PDK材料清单（BOM）:

图13.评估板AFE4300EVM-PDK元件布局图（顶层）

图14.评估板AFE4300EVM-PDK元件布局图（底层）