Simulation of Voltage Controlled Tunable All Pass Filter using LM13700 OTA

Transcription

1 World Aadey of Siene, Enineerin and Tehnoloy nternational Journal of Coputer and Systes Enineerin ol:4, No:8, 2 Siulation of oltae Controlled Tunable All Pass Filter usin LM37 OTA Bhaba Priyo Das, Neville Watson and Yonhe Liu nternational Siene ndex, Coputer and Systes Enineerin ol:4, No:8, 2 waset.or/publiation/8924 Abstrat n reent years Operational Transondutane Aplifier based hih frequeny interated iruits, filters and systes have been widely investiated. The usefulness of OTAs over onventional OP-Aps in the desin of both first order and seond order ative filters are well douented. This paper disusses soe of the tunability issues usin the Matlab/Siulink software whih are previously unreported for any oerial OTA. Usin the siulation results two first order voltae ontrolled all pass filters with phase tunin apability are proposed. Keywords All pass filter, Operational Transondutane Aplifier, Siulation.. NTRODUCTON letronially tunable iruits attrated onsiderable E attention in the desin of analo interated iruits beause different values of resistane, indutane or apaitane an be obtained by the sae devie. Proraability is one the ost attrative features of the Operational Transondutane Aplifier (OTA), sine this akes it possible to tune analo devies suh as; filters, osillators et, eletronially. OTA is a differential voltae ontrolled urrent soure (CCS) where the output urrent is ontrolled by an applied input voltae sinal. This tunability is obtained by varyin the transondutane ( ) of the OTA whih in turn is ontrolled by the urrent or voltae. However, tunability is restrited by the liited bandwidth of, whih depends on the urrent. OTA is a oerially available ative oponent whih has been used widely in any appliations. The first exaple of eletronially tunable filter iruit usin OTA was proposed in []. OTA iruits have been shown to be potentially advantaeous for the desin of any first and seond order hih-frequeny analo filters [2] [6]. There is another ative oponent known as Current Conveyor whih Bhaba Priyo Das is with the Departent of Eletrial and Coputer Enineerin, Univeristy of Canterbury, New Zealand. (Phone: ; e-ail: bpd2@ulive.a.nz). Neville Watson is with the Departent of Eletrial and Coputer Enineerin, Univeristy of Canterbury, New Zealand. Yonhe Liu is with the Departent of Eletrial and Coputer Enineerin, Univeristy of Canterbury and Shool of nforation Enineerin, nner Monolia University of tehnoloy, China. provides a wide rane of tunability [7] but there is a differene in the internal struture and the OTA uses a lower nuber of transistors opared to a urrent onveyor. All pass filters have been exhaustively investiated usin OTA partiularly, where the desin onsideration inludes phase delay [8]-[9]. This work siulates the oerially available LM37 OTA usin the Matlab/Siulink. A voltae ontrolled all pass filter usin LM37 is proposed. Proraability is ahieved by usin an OTA based floatin proraable resistor. Also, a seond iproved version is obtained by addin the rounded proraable apaitane ultiplier [] whih ives it a wider tunable rane.. OTA FUNDAMENTALS An ideal OTA is defined by o ( in+ - in- ) where the input and output resistanes are infinite. The transondutane is iven by: () 2 T where T : theral voltae 26 at roo teperature : urrent. As voltae is the ore easily ontrollable, a iruit is used to onvert the voltae to urrent. Fi. Ciruit sybol of OTA. A siulink blok is reated based on the paraeters speified in [] for the oerial LM37 OTA and the PSPCE odel [2] fro National Seiondutor. The axiu urrent variation is between to 2 A. nternational Sholarly and Sientifi Researh & nnovation 4(8) 2 99 sholar.waset.or/ /8924

2 World Aadey of Siene, Enineerin and Tehnoloy nternational Journal of Coputer and Systes Enineerin ol:4, No:8, 2 nternational Siene ndex, Coputer and Systes Enineerin ol:4, No:8, 2 waset.or/publiation/8924 Fi. 2 Sall sinal odel of OTA. Fi. 3 Developed Siulink odel of LM37.. SMULATON OF FLOATNG RESSTOR Fi. 4 (fro [3]) shows the iruit for siulatin a floatin resistor. Here, o 2 Fi. 4 Ciruit for siulatin floatin resistor. ( ) ( ) 2 (3) o2 2 But, the output urrents are: o and o R (2) (4) Then, etive resistane as seen by terinals at & 2 : 2 (5) Fi. 5 Siulink odel of floatin resistor. Fi. s 6 and 7 show the variation of urrent with ontrol voltae and variation of etive resistane with ontrol voltae respetively. As an be seen, a wide rane of etive resistane an be obtained, fro 2 Ω to 7 kω. Bias urrent (A) -> Effetive resistane (Oh) -> Siulated Bias urrent s Control oltae Control olate () -> Fi. 6 ariation urrent with ontrol voltae. Siulated Effetive resistane s Control oltae Control oltae () -> Fi. 7 ariation positive rounded resistane with ontrol voltae.. PROPOSED TUNABLE ALL PASS FLTER Utilizin the above iruit, the realization of a voltae ontrolled proraable all pass filter is feasible. The proraable phase shifter proposed is shown in Fi. 8 nternational Sholarly and Sientifi Researh & nnovation 4(8) 2 2 sholar.waset.or/ /8924

3 World Aadey of Siene, Enineerin and Tehnoloy nternational Journal of Coputer and Systes Enineerin ol:4, No:8, 2 nternational Siene ndex, Coputer and Systes Enineerin ol:4, No:8, 2 waset.or/publiation/8924 whih utilizes the floatin resistor desribed in setion. The phase shift between the input and output is iven by: θ 2 tan ( ω R C ) (6) Fro Setion, R 2 T (7) 9.2 where T 26 at roo teperature. Fro Fi. 6, the equation of the straiht line is obtained as: y.332 x y.332 ( x ) ( x ) y 2 5 Aain fro Fi. 6 it an be seen that at -3.9, A for R 5 kω. Thus, the relationship between and with R in (kω), is: ( ) A (8) 2 R Fro (5) R 2 R ( ) (9) Substitutin (9) into (6) ives the tunable phase shift as: 2 R θ 2 tan ( ω C ) () 9.2 ( ) Fi. 8 All pass filter based on floatin resistor. Phase shift (Derees)-> Phase shift s Control oltae for LM37 based all pass filter at khz Control oltae ()-> Siulated phase shift obtained Calulated fro froula dedued Fi. 9 Siulated and alulated result obtained fro iruit of Fi. 8.. GROUNDED CAPACTOR MULTPLER [] The analysis of the iruit shown in Fi., ives the etive ipedane as: Z in sc Fro (), etive apaitane is: C C C C Fi. Ciruit for siulatin rounded Capaitor. () (2). SMULATON RESULTS The all pass filter was siulated with R kω, C µf for a voltae sinal at khz. The siulation results are in ood areeent with the alulated phase shift obtained fro ().. MODFED ALL PASS FLTER norporatin the rounded apaitor ultiplier in iruit, the realization of a voltae ontrolled proraable floatin resistor and a proraable rounded apaitor is depited in Fi. 2. The equation for phase shift is now, iven by: nternational Sholarly and Sientifi Researh & nnovation 4(8) 2 2 sholar.waset.or/ /8924

4 World Aadey of Siene, Enineerin and Tehnoloy nternational Journal of Coputer and Systes Enineerin ol:4, No:8, 2 ariation of etive apaitane s b/bo with CnF Ceq (nf) -> b/b -> nternational Siene ndex, Coputer and Systes Enineerin ol:4, No:8, 2 waset.or/publiation/8924 Fi. ariation of etive apaitane for rounded Capaitor with 5 µa. varied fro 5 µa to 2 A and C nf. Substitutin (2) in () ives: 2 R θ 2tan ( ω C) (3) 9.2 ( ) Keepin 5 µa i.e -6.4 fixed 2 R θ 2 tan ( ω C) 9.2 ( ) R θ 2 tan ( ω G C) (4) 9.2 ( ) The all pass filter is siulated with R kω, C µf for a voltae sinal at khz. The phase shift variation is fro 38 to 77 for variation fro 5 to 3.7 for iruit in Fi. 2. Usin G.25 i.e 2, a wider tunable phase shift is obtained as shown in Fi. 3. t is evident fro Fi. 3 that for sae ontrol voltae, a wider phase shift fro to 76 is obtained in the proposed iruit as opared to the one in Fi. 8 where the lower liit starts at 38 for a khz sinal. This wider phase shift variation has been obtained due to the rounded apaitane ultiplier added in the iruit of Fi. 8. This iruit has been siulated for Hz, khz and khz.. CONCLUSON n this paper, eletronially tunable resistors and apaitors are siulated in MATLAB/Siulink usin the LM37 odel developed. Both rounded and floatin onfiurations are disussed. Tunability issues for these iruits with respet to the ontrol voltae are presented. Most of these follow an exponential relation with the ontrol voltae. A siple voltae ontrolled all pass filter is proposed where the phase shift depends on the applied ontrol voltae. <-Phase shift (Derees)-> Fi. 2 Proposed odified wider tunable all pass filter Phase shift s Control voltae for LM37 based all pass filter Control oltae ()-> Phase shift usin iruit in Fi. 8 Phase shift usin iruit in Fi. 2 Fi. 3 Coparison of siulation results for the proposed iruit and the iruit in Fi. 8. The eletronially tunable rounded apaitor ultiplier usin two OTAs and one Op-Ap is used. This onfiuration is apable of both enhaneent and attenuation ains. Based on this apaitane ultiplier, the siple all pass filter proposed here obtains a wider phase shift. A ontinuous phase an be obtained with a proper hoie of apaitane and in resistane. REFERENCES [] S. Frano, Use transondutane aplifier to ake proraable ative filters. Eletroni Desin, 24(9), 976, pp. 98. [2] R. L. Geier, E. Sanhez - Sinenio, Ative filter desin usin operational transondutane aplifiers: A tutorial, EEE Ciruits and Devies Maazine,, 985, pp [3] A. Urbas, J. Osiowski, Hih-frequeny realization of C-OTA seondorder ative filters, Proeedins of nternational Syposiu on Ciruits and Systes (SCAS), 3, 982, pp [4] H. Malvar, Eletronially ontrolled ative filters with operational transondutane aplifiers, EEE Transations on Ciruits and Systes, CAS-29, 982, pp [5] T. Deliyannis, Y. Sun, & J. K. Fidler, Continuous tie ative filter desin Boa Raton: CRC Press, 999, Ch-8. [6] Y. Sun, Desin of hih frequeny interated analoue filters. London: EE Press, 22. nternational Sholarly and Sientifi Researh & nnovation 4(8) 2 22 sholar.waset.or/ /8924

5 World Aadey of Siene, Enineerin and Tehnoloy nternational Journal of Coputer and Systes Enineerin ol:4, No:8, 2 [7] A. J. Martin, J. Rairez-Anulo, R. G. Carvajal, Desin of hihperforane tunable filters based on urrent onveyors, Proeedins of 25 European Conferene on Ciruit theory and desin, ol. 2, 25, pp. /3-/6. [8] N. A. Shah, S. N. Ahad, Eletronially tunable OTA-based all-pass iruit, nternational Journal of Eletronis, 68(6), 99, pp [9] M. Abuelaati, U. Baroudi, A proraable phase shifter for sinusoidal sinals, Ative and Passive Eletroni Coponents Journal, ol. 2, 998, pp.7-2. [] M. T. Ahed,. A. Khan and N. Minhaj, "Novel eletronially tunable C-ultipliers," Eletronis letters, vol. 3, no., 995, pp. 9-. [] Datasheet- LM37 Dual Operational Transondutane Aplifiers with linearizin diodes and buffers. National Seiondutor, 24. [2] [3] Kendall. Su, Analo Filters, Kluwer Aadei Publishers, 23, Ch-4. nternational Siene ndex, Coputer and Systes Enineerin ol:4, No:8, 2 waset.or/publiation/8924 nternational Sholarly and Sientifi Researh & nnovation 4(8) 2 23 sholar.waset.or/ /8924