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1、db的概念和含义DBconceptandmeaning,・Txt-twopeopleatthesametimemadeamistake,standuptobearthesidecalledtolerance,theothersideoweddebt,soonerorlaterhavetoreturn.-donotloveisnotlove,don'tfuckingsaywe.DB(Decibel,DB)isapurecountingunit,originallymeanttoindicatetheratioofthetwovariables,nounits・Inengineer
2、ingapplications,seeminglydifferentdefinitions(justlookingdifferent)areoftenseen・Forpower,clB=10*lg(A/B).Forvoltageorcurrent,dB=20*lg(A/B).Here,A,Brepresentthepowervaluesorcurrentandvoltagevaluesthatparticipateinthecomparison.Themeaningofissimplyabriefrepresentationofthenumberoflarge(followed
3、byalongstringof0)orverysmall(infrontofalongstringof0).DB(application)(suchasheretopowerasanexample):X=100000二1(T5X(dB)二10*lg(X)dB=10*lg(10®dB=50dBX二0.000000000000001二1(T—15X(dB)二10*lg(X)dB=10*lg(10=15)dB=-150dBingeneral,inengineering,dBanddBnotonlyadditionandsubtraction,multiplicationanddivi
4、sion.Whichisthemostusedmethod:dBmminusdBmisactuallytwophasepower,signalpowerandnoisepoweristhedivisionofsignal-to-noiseratio(SNR)・Forexample:30dBm-OdBm=lOOOmW/lmW=1000=30dB.DBmplusdBmisactuallytwopowermultiplication,withoutactualphysicalmeaning・Inthefieldofelectronicengineering,theamplifierg
5、ainisdB(DB).Theratiobetweentheamplifieroutputandtheinputistheamplificationfactor,theunitis"times",suchas10timesamplifier,100timesamplifier・Whenusing"decibel"asaunit,theamplificationiscalledgain,whichisthetwonameofaconcept・TherelationshipbetweenconversiondBandmagnificationofelectricityis:A(V)
6、(dB)=201g(Vo/Vi):voltagegainA(I)(dB)=201g(Io/Ii);currentgainofAp(dB)=101g(Po/Pi);powergainDBdefinitionofvoltage(current)withdifferentgainandpowergainformulabut,weallknowthattherelationshipbetweenpowerandvoltageandcurrentisP=厂2/R二「2*R.Withthisformula,thegainvaluesofthetwoarethesame:lOlg[Po/P
7、i]=101g[(Vo^2/R)/(Vi/2/R)]二201g(Vo/Vi).Note:ThisappliesonlytoRi二Rocircuits,suchasinCATVsystems,wherethematchingimpedanceofeachdeviceis75.Therearethreemainbenefitsofusingdecibelsasaunit・(1)thevalueissmallerandeasiertoreadandwrite・Thetotalmagnificati
