单片机外文文献翻译基于MSP430的FSK调制解调.docx

单片机外文文献翻译基于MSP430的FSK调制解调.docx

《单片机外文文献翻译基于MSP430的FSK调制解调.docx》由会员分享，可在线阅读，更多相关《单片机外文文献翻译基于MSP430的FSK调制解调.docx（39页珍藏版）》请在冰点文库上搜索。

单片机外文文献翻译基于MSP430的FSK调制解调

中文翻译材料

英文题目FSKModulationandDemodulation

WiththeMSP430Microcotroller

中文题目基于MSP430的FSK调制解调

学院：

计算机科学与技术学院

专业：

通信工程

学生姓名：

指导教师：

二O一三年六月

IMPORTANTNOTICE

TexasInstrumentsanditssubsidiaries（TI）reservetherighttomakechangestotheirproductsortodiscontinue

anyproductorservicewithoutnotice,andadvisecustomerstoobtainthelatestversionofrelevantinformation

toverify,beforeplacingorders,thatinformationbeingreliedoniscurrentandcomplete.Allproductsaresold

subjecttothetermsandconditionsofsalesuppliedatthetimeoforderacknowledgement,includingthose

pertainingtowarranty,patentinfringement,andlimitationofliability.

TIwarrantsperformanceofitssemiconductorproductstothespecificationsapplicableatthetimeofsalein

accordancewithTI’sstandardwarranty.Testingandotherqualitycontroltechniquesareutilizedtotheextent

TIdeemsnecessarytosupportthiswarranty.Specifictestingofallparametersofeachdeviceisnotnecessarily

performed,exceptthosemandatedbygovernmentrequirements.

CERTAINAPPLICATIONSUSINGSEMICONDUCTORPRODUCTSMAYINVOLVEPOTENTIALRISKSOF

DEATH,PERSONALINJURY,ORSEVEREPROPERTYORENVIRONMENTALDAMAGE（“CRITICAL

APPLICATIONS”）.TISEMICONDUCTORPRODUCTSARENOTDESIGNED,AUTHORIZED,OR

WARRANTEDTOBESUITABLEFORUSEINLIFE-SUPPORTDEVICESORSYSTEMSOROTHER

CRITICALAPPLICATIONS.INCLUSIONOFTIPRODUCTSINSUCHAPPLICATIONSISUNDERSTOODTO

BEFULLYATTHECUSTOMER’SRISK.

Inordertominimizerisksassociatedwiththecustomer’sapplications,adequatedesignandoperating

safeguardsmustbeprovidedbythecustomertominimizeinherentorproceduralhazards.

TIassumesnoliabilityforapplicationsassistanceorcustomerproductdesign.TIdoesnotwarrantorrepresent

thatanylicense,eitherexpressorimplied,isgrantedunderanypatentright,copyright,maskworkright,orother

intellectualpropertyrightofTIcoveringorrelatingtoanycombination,machine,orprocessinwhichsuch

semiconductorproductsorservicesmightbeorareused.TI’spublicationofinformationregardinganythird

party’sproductsorservicesdoesnotconstituteTI’sapproval,warrantyorendorsementthereof.

Copyright♥1998,TexasInstrumentsIncorporated

Contents

1Introduction...................................................................................………………………1

2DemodulationTheory..........................................................................

2.1ChoosingtheSamplingRate...............................................................

2.2FrontEndProcessing.....................................................................

2.3FSKDemodulation........................................................................

2.4BitSynchronization.......................................................................

3ModulationTheory.............................................................................

3.1ChoosingtheSamplingRate...............................................................

3.2ConstructingtheLookUpTable............................................................

3.3FSKModulation..........................................................................

2

2

2

2

3

4

4

4

4

4DataConversion..............................................................................………………………..5

4.1A/DConversion.........................................................................………………………….5

4.2D/AConversion.........................................................................………………………….5

5PowerConsumption...........................................................................………………………6

6ExercisingtheSoftware........................................................................…………………………7

6.1FSKReceiver...........................................................................…………………………..7

6.2FSKTransmitter.........................................................................…………………………..7

7ExampleCircuits..............................................................................………………………...8

7.1UsingtheMSP430C325asMainProcessor.................................................……………………………….8

7.2ExampleTelephoneInterface.............................................................……………………………..8

8Summary.....................................................................................……………………….10

9References..................................................................................………………………….11

FSKModulationandDemodulationWiththeMSP430Microcontroller

i

FSKModulationandDemodulationWiththeMSP430

Microcontroller

ABSTRACT

ThisapplicationreportdescribesasoftwareprogramforperformingV.23FSKmodem

transceiverfunctionsusinganMSP430microcontroller.Itmakesuseofnovelfilter

architecturetoperformDSPfunctionsonaprocessorwithonlyshiftandaddcapabilities.

1Introduction

Manymeasurementapplications（forexample,electricandgasmeters）require

awaytocommunicateelectronicallywithacentralofficesothatmeasureddata

canbereportedbacktothecentralofficeandnewtariffscanbesetintheremote

site.Telephonyprovidesaconvenientmeansofdatacommunication.

Frequencyshiftkeying（FSK）anddualtonemultifrequency（DTMF）aretwo

popularmethodsofrepresentingbinarydataovertelephonecircuits.This

applicationreportdescribesaV.23-compliantFSKtransceiversoftwaremodule.

Integratingthemeasurementandcommunicationfunctionsontothesamechip

yieldscostaswellaspower-savingbenefits.UsingtheMSP430,ahighMIPsultra

lowpowermicroprocessor,allowspowertobedrawnfromthetelephonelinein

somecases.

ThisreportdescribesthemathematicalformulasforFSKsignaltransmissionand

detection.Alistofthesoftwaremodulesisincludedwithareferenceschematic

fortelephoneinterfaceandlowcostA/Dconverter.Theschematicisonlya

reference,sincethepreciseimplementationcanvaryfromcountrytocountry.

1

DemodulationTheory

2DemodulationTheory

AquadraturedemodulatorprovidestheFSKdemodulation.Inthistypeof

demodulation,thesignalanditsdelayedversionaremultipliedtogetherandthen

low-passfiltered.Ifthedelay,T,issetsuchthatWcarrier⋅T=ð/2,thenthe

low-passfilterresultisproportionaltothefrequencydeviationfromthecarrierand

thereforerepresentsthebitvaluesent.

IfwWcarrier

wherew=2π⋅f:

+

"WdeltaandT

+

Wcarrier

+p2

³

2.1

cos[wt].cos[w（t–T）]coswT

coswTsin["Wdelta]

+

）cos（2wt–wT）³LowPassFilter

+"sin[Wdelta]

_

ChoosingtheSamplingRate

ThesamplingischosentobeFcarrier4forthepurposeofobtainingthe

delayedsamplewithoutcomputationaloverhead.ForV.23,theFcarrier

frequencyis1700Hzandthereforethesamplingratebecomes6800Hz.Using

a32768-Hzcrystalyields6793.3Hz,whichis0.1%out.Thesamplingfrequency

issetbythe8-bitintervaltimer.Becausethistimerislimitedto256counts,the

interruptratedissettotwicethesamplingrateandtheprocessingisdividedinto

twohalveswithsignalsamplingperformedeveryotherinterrupt.

2.2

FrontEndProcessing

MostA/Dconverters,includingthesuccessiveapproximationA/Dconverterin

theMSP430C325,needadcbias;thisyieldsanunsignedintegersamplewith

anoffset.Beforethissamplecanbeprocessedfurther,itneedstogothroughan

unbiasfiltertotakeoutthedcbiasandturnthesampleintoasignedintegervalue.

Thisunbiasfilteringalsogives30dBorsoofrejectionformainfrequencies.

2.3

FSKDemodulation

Thesignedintegersampleanditsdelayedversionaremultipliedtogether;inthis

application,an8×8signedmultiplicationloopisused.

Theproduct,madeupoftwofrequencyelements,islow-passfilteredtoremove

thedoublefrequencyelement.Theremainderisasignedintegervalue

representingtheoriginalbitvaluetransmitted.

Thelow-passfilterusesthedigitalwavefilteringtechnique.Thistechniquegives

stablecharacteristicswithverygoodcoefficienttolerance.Allmultiplicationis

donethroughshiftsandaddswithth