A High Q Band Pass Filter Using Two Operational Amplifiers

Transcription

1 Jurnal f Physcal Scences, l., 007, A Hgh Q Band Pass Flter Usng Tw Operatnal Amplfers Seema ana*, Kapl Dev Sharma** and Krat Pal*** *DA Centenary Publc Schl, Hardwar INDIA **Department f Physcs, DA(PG) Cllege, Dehradun(Uttranchal) - INDIA ***Department f Earthquake Engneerng I. I. T. rkee 7 667,INDIA E-mal: krat.pal@gmal.cm eceved February, 007; accepted Aprl 0, 007 ABSTACT A hgh Q band pass flter usng tw peratnal amplfers s reprted. The qualty factr Q f the crcut s cntrllable thrugh a sngle resstance. The results f expermental and theretcal studes are presented and cnfrms the thery.. Intrductn The applcatn f band pass flter fr selectng a band f frequences s well knwn n the pen lterature. In general frm the transfer functn f a band pass flter s gven by a T (s) = s () a b s b s where a, a, b and b are cnstants. The qualty factr Q f the band pass flter s gverned by the term b. It has nfnte Q f b appraches zer value but practcally t s nt pssble althugh sme hgh value up t Q=0 s easly pssble. In the lterature number f crcuts f band pass flter usng peratnal amplfers are avalable [-5]. Here the new crcut f band-pass flter usng nly tw peratnal amplfer s presented whch has a cntrllable Q thrugh a sngle resstance. The expermental results cnfrm the thery.. Crcut Descrptn Cnsder the general crcut shwn n fg..its vltage transfer functn s gven by Z3 / Z = () Z Z 3 ( ) Z5Z f Z = Z 33

2 3 Seema ana, Kapl Dev Sharma and Krat Pal Z3 / Z = Z 3 Z Z Z 5 (3) put sc Z = sc cmbnatn f n parallel wth C Z 3 = ( sc) resstance n seres wth C Z = and Z 5 = 5 Equatn (3) becmes sc s C sc( K) () where K = 5 The actual crcut s shwn n fg.. The equatn () represents a hgh Q band pass transfer functn whch s cntrllable thrugh r 5.Fr snusdal nput s = jω the equatn () becmes 0 jωc = (5) ( ω C jωc( K) put ωc = u (nrmalzed frm), equatn(5) becmes ju = (6) ( u ) ju( K) Center frequency u 0 =,and gan max = K s maxmum at ths value whch s gven by (7)

3 A Hgh Q Band Pass Flter Usng Tw Operatnal Amplfers 35 Z Z 3 Z 5 O.A Z O.A 0 Z Fg.. The General Crcut C C O.A C O.A 5 0 Fg.. Actual Crcut f Hgh Q Band Pass Flter

4 36 Seema ana, Kapl Dev Sharma and Krat Pal The lwer and upper cutff frequency u l and u h ccurs at,e at, and are gven as ( K) ( K) u l = ( K) f maxmum gan (8) ( K) ( K) u h = (9) The bandwdth f the flter crcut s gven by B.W. = u h u Or B.W. = ( K) (0) u The qualty factr Q = u h u l r Q = () ( K) It s clearly seen frm eqn.() that Q appraches nfnty as K apprach the value.0.the Q can be cntrlled by r Expermental esults The crcut was tested fr =0KΩ,C=0.00µF, 5 =0KΩ and =5KΩ n frst experment and fr =0KΩ,C=0.00µF 5 =0KΩ and =8KΩ n secnd experment. The IC 30 whch s an peratnal amplfer was used and perated wth a ± pwer supply. An nput sgnal f 00m was gven n the frequency range f KHz t 00KHz. The results fr K= / 5 =.5 and K=.8 are shwn n fgure -3 and fgure- respectvely.

5 A Hgh Q Band Pass Flter Usng Tw Operatnal Amplfers 37 FEQUENCY ESPONSE CUE FO K=.5.5 GAIN (db) THEOITICAL EXPEIMENTAL FEQUENCY (Hz) Fg.3. Frequency espnse f Band Pass Flter (K=.5) FEQUENCY ESPONSE CUE FO K= GAIN (db) FEQUENCY (Hz) THEOITICAL EXPEIMENTAL Fg.. Frequency espnse f Band Pass Flter (K=.8)

6 38 Seema ana, Kapl Dev Sharma and Krat Pal. Cnclusns A new type f band pass flter crcut has been reprted. The crcut realses a hgh Q band pass flter, whch s cntrllable thrugh a sngle element as a resstance. The results f expermental study cnfrm the theretcal predctns made. EFEENCES [] Actve Inductrless flters edted by S.K. Mtra. Ed. IEEE press, Inc. New Yrk.97. [] Mdern Actve flter Desgn edted by. Schauman, M.A. Sderstrand, K.. Lader. edtn. IEEE press. Inc. New Yrk, p.63, 98. [3] Actve flter Desgn Hand Bk edted by G.S. Mschytz and P. Hrn edtn, Jhn Wley & sns, New Yrk. Brsbane Trnt.p.70,98. [] Actve flters fr cmmuncatns and nstrumentatns edted by P. Brwn and F.W. Stephensn, McGraw Hll Bk Cmpany U.K. Ltd., p-6, p-5, p-6, p-65, p-70, p-75, p-79 and p- 0.,979. [5] eddy M.A. An Insenstve Actve.C. Flter fr hgh Q and hgh frequences. IEEE Trans. CAS 3 N 7 pp. 9-33, 976.