About Oscillators with Current Conveyors and De-Phasing Circuit with Current Divisor

Transcription

1 Aout Oscllators wth Current Conveyors and De-Phasng Crcut wth Current Dvsor LUIZA GRIGORESCU, IOANA DIACONESCU, Engneerng Faculty of Brala, Dunarea de Jos Unversty of Galat Calea Calaraslor nr. 9, Brala ROMANIA Astract: - In ths paper t was made a RC llator and ts transfer functon, and t was made a study of errors whch affects frecquency of llaton. The paper pont out the expermental results otan through RC llator mplementaton wth PA 63A current-conveyors showng that the current mode llators appears to e an nterestng approach from the perspectve of the smplcty/performance compromse. Key-Words: - frequency, llator, de-phasng crcut Introducton Ths paper proposes a systematc approach on the generaton of second order current mode RC llators (CMO-RC). Theoretcally such current amplfers can e easly otaned, and the use of the complementary polar process can e now used for the practcal mplementaton of such hgh performance amplfers. The generaton s done y startng from a classfcaton of the reactve llators desgned y lnear frequency selectve networ, a current repeater and an deal current amplfer. Ths classfcaton s made y the current transfer rato of the opened loop otanale whle the loop s roen on ether the nput or the output of the current amplfer. For a gven llator, should the amplfer and selectve networ e correctly dentfed, the transfer functon s unque. The loc schema of a reactve RC llator s presented n fgure, where y A we mean an deal current amplfer (amplfer trans-resstance or trans-conductance), whose gan s A= () For a lnear second order RC networ, the current transfer functon can e descred as β ( s) a s + a s+ a = s s + + () where s= jω s the complex frequency value and a n (n=,,) are real numers. In practce only stale networs are of nterest so the n (n=,,) coeffcents must e postve real numers. Current uffer s an deal current amplfer wth unt gan and havng an mpedance adapter role etween amplfer and the selectve networ. Because the selectve networ output current has to e a short crcut current and ecause the nput amplfer has hgh mpedance than the uffer presence s a must. To calculate the llatng frequency and the gan of the amplfer from Fgure, ths has to self- start and to eep the snusodal llatons, so t has to e appled Barhausen formula, vald for any feedforward llator, β A=. The values of coeffcents from () for whch formulas (3) and (4) have physcs meanng wll gve us all transfer functons shapes acceptale for harmonc llator s constructon. Fg.. The deal current llator ISBN:

2 For the crcut n fgure wth the closed reacton loop, the ω angular llaton frequency and the llaton mantanng necessary gan (G ) have the elow expressons ω = G (3) = (4) a The aove scopes wll e further called the llaton frequency and mantanng gan. Snce the gan n (4) must e fnte, the a can t e zero whle expresson (4) allows for a and a to e zero oth smultaneously and each at a tme. Practcal mplementatons Our proposed llator scheme s an llator wth de-phasng crcut wth current dvsor and grounded capactor, wth a CR net wth a sngle secton, separated trough a current amplfer. The llator s the second type one and ts net transfer functon coeffcents respect the followng condtons: a =, a, a. The llator transfer functon result y multply those two nets transfer functons followed y multplcaton wth amplfers gan and has the followng form (5): ( ) ( ) s RR CC s RC RC AAR C + AA = (6) RC + RC A ARC = (7) R C G = A= + R C (8) G s the mantanng gan. Avalale lmts for varaton are gven y restrcton: R R < < + (9) C C For partcular case R =R, C =C, the mantanng gan ecomes: G = () Comng ac to (6) and nowng that A = and s= jω t can e calculated llaton frequencyω : RC j ω R RCC + + ( ) = RC ω R C + R C = R R C C () () ω R C = + R R C RCC (3) Fg. Oscllator wth de-phasng crcut and CR net wth a sngle secton = A A s R R C C ( ) + src + s( R C + R C ) + (5) Usng relaton (5) and also the Barhausen relaton t can e measured the gan and pulsaton necessary to eep snusodal llaton. RC Notng wth S = + scale RC factor for whch R =R, C =C, has the value S =. Into ths stuaton, varaton lmts ecome: < < (4) ISBN:

3 The top edges gven y relatons (9) and (4) for are meanngless ecause hgh value equals unt. Practcally speang, ths means that there are no restrctons for value. Amplfer A can not mssng ecause t has also the role to separate the used nets. The scale factor can e modfed etween zero and nfnte. Ths can get for very restrcted varatons of G. For partcular stuaton of resstances and capactes respectvely equals, the scale factor for the crcut from Fgure can e modfed etween unt and nfnte, whle vares etween zero and unt. For the created llator, the requred gan for the sustanng of a unary transfer raton n the loop, was ensured y the frst dfferental stage, all the other actve stages, havng a unary gan. One can t dscard the use of the current repeatng stage ecause we requre the RC de-phasng networs to e evaluated aganst ther current ehavor. For the mplementaton of a SIDO stage we requre two PA63 current conveyors, whle for the mplementaton of a current repeater there was only one PA63 current conveyor requred. To avod the latch-up phenomenon specfc to the PA63 current conveyor, we wll use (f requred) on the Z outputs of the conveyor, some 3.6V Zenner dodes (DZ3V6), n seres wth N448 fast dodes, as shown n the PA63 catalogue. Ovously the use of such dodes wll lead to a change n the loop transfer rato and also of the llaton ampltude. The conveyors polarzaton was done accordng to the catalogue schemas, y ensurng a polarzaton current of.6ma. In order to mplement the RC dephasng crcuts, we used % tolerance metal fol resstors, hgh precson capactors (-% precson) and hgh tolerance electrolytcal capactors (-5) % tolerance. The correctness of the crcut runnng has een verfed usng specalzed OrCAD PSpce.5 soft. The current conveyors we're desgned y NS 395 and NS394 transstors (see fgure 3), and the otaned shapes of waves are n Fgure 4. Fg. 3 RC llator wth PA63 ISBN:

4 Fg. 4 The results of the numercal smulaton wth PSpce In followng lael could e notced the evoluton of measured frequency values opposte the calculated ones, when the C and C value 47nF. It s notced that for R and R values growng the frequences values are decreasng (oth measured and calculated values) untl ts equals and so the relatve value decreases, too. Tale No. R =R [ Ω ] Measured frequency [Hz] Calculated frequency[hz] Relatve error[%] , , , K ,8 8 3K 9 5K Conclusons Ths paper showed that usng of current mode crcuts has some practcal advantages confronted y conventonal devces wth voltage operatng mode, such as hgher worng speed and etter worng lnearty. Speang aout ths aspect, one of ths paper goal s, frst of all, to show that the current mode crcuts can e used to produce hgh frequency llatons and to show n what condtons ths could e happened. It s usual that the electronc devce performances used n llators to e expressed y some feature of output sgnal, such as: maxmum frequency, frequency stalty, dstorton level. Speang aout the hghest lmtaton of worng frequency, ths depends of many ntrnsc parameters of the semconductor or of the electronc devce desgn. Hgh operatng speeds, meanng hgh frequency of llatons, offer many other devces wth semconductors such as semconductors of polar types or wth feld effect, dodes wth negatve resstance whch are already used n very hgh frequences technque. Frequency stalty depends, frst of all, y stalty of passve elements values wth envronment factors, of whch the most mportant s the temperature the others such as humdty and pressure have low nfluences. The electronc devce temperature produced y the envronment or y dsspate energy on devce can affect the frequency stalty frequency less than passve elements. The temperature nfluence can e reduced through a judcous semconductor mcrochp desgn so that dsspatve hgh power junctons to carry out an ntensve heat transfer towards external surface. One oserves the stalty of the ampltude and the llaton frequency otaned wth the current mode llator s superor the ones otanale y means of voltage mode crcuts. ISBN:

5 References:. Toumazou, C., Ldgey, F.J., Hagh, D.G. Analogue IC Desgne: The Current Mode Approach.. Toumazou, C., Ldgey, F.J., and Cheung, P.K. Current actuated analogue sgnal processng crcuts: Revew and recent developments. Procs 988 IEEE Int Symp Crcs and Systems (Portland, USA), pp , June Hagh, D.G., Taylor, J.T., Sngh, B., Low senstvty swtched capactor smulaton of ellptc lowpass LRC lader flters, Electroncs Letters, vol 4, no, 7 th January 988, pp Sedra, A.S., and Bracett, P., Flter Theory and Desgn: Actve and Passve, Matrx Pulshers, Temes, G.C., LaPatra, G., Introducton to Crcut Synthess and Desgn, McGraw-Hll Schaumann, R. Ghaus, M.S., Laer, K.R., Desgn of Analog Flters: Passve, Actve RC and Swtched Capactor, Prentce Hall, Par, C.S., Schaumann, R., A Hgh-Frequecy CMOS Lnear Transconductance Element, IEEE Trans. Crcuts Syst., Vol. CAS-33, pp 3-38, Grgorescu, L, Amplfers ult wth currentconveyors, Romanan Journal of Physcs, Pulshng House of the Romanan Academy, Volume 53, Numer - 8, pg.5-, ISSN -46X, Grgorescu, L., Impedance converters, Romanan Journal of Physcs, Pulshng House of the Romanan Academy, Volume 53, Numer - 8, pg.9-4, ISSN -46X.. Stancu C., Grgorescu L., Cracun N., Research Concernng the use n Agrculture of Ash Resulted from Burnng Pulp and Paper Industry s Wastewood, Journal of Envronmental Protecton And Ecology, Volume, Issue 3, pp. 4-48, ISSN 3-565,.. Grgorescu L., Daconescu I., Desgn of current mode llators y current conveyors, Proceedngs of the st WSEAS Internatonal Conference on Sensors and sgnal (SENSIG 8), Bucharest, Romana, Novemer 7-9, 8, ISSN:79-57, ISBN: , Pulshed y WSEAS Press,, pg.6-.. Grgorescu, L., Research on Current Amplfer wth Current Conveyor Actve Loads, Proceedngs of the 8 th WSEAS Internatonal Conference on Sgnal Processng, Istanul, Turey, Ma 3-June, 9, pg. 5-55, ISSN 79-57, ISBN Grgorescu, L., Daconescu, I., Smonescu, C., Fourer Transform and ts applcaton, Proceedngs of the 3 th WSEAS ntl. Conference on Mathematcal Method and Computatonal Technques n Electrcal Engneerng (ACMMA ), Angers- France, 7-9 nov., pg. 4-46, ISBN; ISBN: