FILTER DESIGN PROGRAM FOR

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1、®APPLICATIONBULLETINMailingAddress:POBox11400•Tucson,AZ85734•StreetAddress:6730S.TucsonBlvd.•Tucson,AZ85706Tel:(602)746-1111•Twx:910-952-111•Telex:066-6491•FAX(602)889-1510•ImmediateProductInfo:(800)548-6132FILTERDESIGNPROGRAMFORTHEUAF42UNIVERSALACTIVEFILTERByJohnnieMolinaandR.MarkStitt(602)746-

2、7592Althoughactivefiltersarevitalinmodernelectronics,theireliminatessignalsabovethecutofffrequency(inthestop-designandverificationcanbetediousandtimeconsuming.band),andperfectlypassessignalsbelowit(inthepass-Toaidinthedesignofactivefilters,Burr-Brownprovidesaband).Inrealfilters,varioustrade-offs

3、aremadeinanseriesofFilterPro™computer-aideddesignprograms.Us-attempttoapproximatetheideal.SomefiltertypesareingtheFILTER42programandtheUAF42itiseasytooptimizedforgainflatnessinthepass-band,sometrade-offdesignandimplementallkindsofactivefilters.TheUAF42gainvariationorrippleinthepass-bandforasteep

4、errateofisamonolithicICwhichcontainstheopamps,matchedattenuationbetweenthepass-bandandstop-band(intheresistors,andprecisioncapacitorsneededforastate-variabletransition-band),stillotherstrade-offbothflatnessandratefilterpole-pair.Afourth,uncommittedprecisionopampisofroll-offinfavorofpulse-respons

5、efidelity.FILTER42alsoincludedonthedie.supportsthethreemostcommonlyusedall-polefiltertypes:FiltersimplementedwiththeUAF42aretime-continuous,Butterworth,Chebyshev,andBessel.ThelessfamiliarIn-freefromtheswitchingnoiseandaliasingproblemsofverseChebyshevisalsosupported.Ifatwo-poleband-passswitched-c

6、apacitorfilters.Otheradvantagesofthestate-ornotchfilterisselected,theprogramdefaultstoaresonant-variabletopologyincludelowsensitivityoffilterparameterscircuitresponse.toexternalcomponentvaluesandsimultaneouslow-pass,Butterworth(maximallyflatmagnitude).Thisfilterhasthehigh-pass,andband-passoutput

7、s.Simpletwo-polefiltersflattestpossiblepass-bandmagnituderesponse.AttenuationcanbemadewithaUAF42andtwoexternalresistors—seeis–3dBatthedesigncutofffrequency.AttenuationbeyondFigure1.thecutofffrequencyisamoderatelysteep–20dB/d