Simple electronically tunable oscillators

Transcription

1 Smple electrncally tunable scllatrs Mlan Strk, Petr Wessar, and Kaml Ksturk,, epartment Appled Electrncs and Telecmmuncatns/RIE, Faculty Electrcal Engneerng, Umversty West Bhema, zech Republc Abstract Ths paper presents derent types electrncally tunable scllatrs; therere requency such scllatrs can be cntrlled by vltage r current. The square wave utput and snusdal utput scllatrs are presented. All descrbed scllatrs have ptental usng n derent applcatn n telecmmuncatns and measurng devces, e.g. phase lcked lps, mdulatn and detectn. The scllatrs were cnstructed and measured. Inc.), ers db dynamc range, ast respnse tme, and very hgh dark resstance. Sme techncal parameters r VTL [] are: Mn. slatn % Rel. humdty: VRMS; Max. resstr pwer: mw; Max. resstr vltage: V; Max LE current: ma; Respnse tme t % nal R ON. ms. The measured utput resstance vs. nput current s shwn n Fg. where lgarthmc scales are used r bth the X and Y axes.. Intrductn Electrncally tunable scllatrs (EO) s ne the mprtant basc buldng blcks n analg and dgtal crcuts. Fr example, n telecmmuncatns t s used r phase mdulatrs, quadrature mxers [], and sngle-sdeband generatrs []. In measurement system, EO s emplyed r vectr generatr r selectve vltmeters []. Fr example, a VO s the man buldng blck n phase lcked lp (PLL) and clck generatr crcuts. There are tw man classes scllatr: relaxatn and snusdal. Relaxatn scllatrs generate the trangular, sawtth and ther nnsnudal waverms. It s pssble use derent apprach r requency cntrl (and ampltude stablzatn snusdal scllatrs), eg. dgtal ptentmeters [, ] r trancnductance peratnal amplers [, ]. Ths paper presents the desgn several types smple scllatrs whch are cntnuusly tunable. The requency changng r several scllatrs s based n ptcally cupled phtresstr (Vactrl) wth db dynamc range []. Fr vltage cntrl the ptcally cupled phtresstrs are cnnected t lnear vltag-current cnverters. It s mprtant t nte that dgtal ptentmeters can be used as well. Fg.. The ptcally cupled phtresstr - Vactrl.. The ptcally cupled phtresstrs prpertes The ptcally cupled phtresstrs cnssts LE dde and phtresstr (Fg. ). A phtresstr r lght-dependent resstr (LR) r phtcell s a resstr whse resstance decreases wth ncreasng lght ntensty. Optcally cupled phtresstr (), als called phtresstve pt-slatr r vactrl (ater a generczed trademark ntrduced by Vactec, R Fg.. The Output resstance vs. nput current r VTL.. ntrlled rng scllatr A cnventnal rng scllatr uses N dd numbers nverter stages (delay stages), cnnected n a clse lp chan [9]. The rng scllatrs have numerus useul eatures, e.g.: It can be easly desgned wth derent types technlgy, t can acheve ts scllatns at lw vltage, t can prvde hgh requency scllatns wth dsspatng lw pwer, t can be electrcally tuned, t can prvde multphase utputs etc. The cnventnal rng scllatr based VO uses varable bas currents t cntrl ts scllatn requency. Hwever, when the bas current s qute small, the vltage swng the VO wll becme slwer (lnger rse/all tme). That s nt desrable n sme applcatns. Assume that the gates t surce parastc capactances are equal. The requency the rng scllatr [] can be und as Nτ = [Hz, s] () where τ s the delay the nverter stage. Ths paper prpses a new type a VO rng scllatr where requency s cntrlled by ptcally cupled phtresstr. The crcut 9

2 dagram s shwn n Fg. where ne phtresstr s used. Such rng scllatr has derent delay and therere requency (r N=) s = [Hz, s] () + ( τ τ ) where τ s delay stage wth phtresstr and τ s delay ther stages. The τ s τ = k = k [s, Ω, A, V] () R d V where k s cnstant, R s phtresstr resstance, capactr, d s current thrugh the LE dde and V nput vltage. Substtutng () nt () wll gve Fg.. The spread spectrum vltage cntrlled rng scllatr In Fg. s shwn measured utput requency vs. nput vltage (sld lne) and apprxmatn (dash lne) gven by V = k + τ V ( k + τ V ) [Hz, F, V] () I V R V I Fg.. The crcut dagram relaxatn scllatr wth utput buer. R =k; = pf; -TL; I - 9, -. ptcally cupled phtresstrs VTL R Fg.. The Vltage cntrlled stage rng scllatr. R =k; = pf; -TL; I - H. 9 y = -.*x +.*x -. O Vcc [V] Fg.. The Output requency vs. nput vltage r relaxatn scllatr wth Vcc= [V] (sld lne), apprxmatn dash lne V [V] Fg.. Output requency vs. nput vltage r rng scllatr measured (sld lne), smulatn dash lne..v ( +.V ) [MHz, F, V] () It s mprtant t nte that eq. () s vald r = pf and R = kω []. In sme applcatns the spread requency spectrum s advantage. The measures spread spectrum rng scllatr s dsplayed n Fg.. 9 y =.*x -.9*x + *x -. Fg.. Output requency vs. supply vltage r relaxatn scllatr wth cnstant V= [V] (sld lne), apprxmatn dash lne 9

3 . ntrlled relaxatn scllatr The relaxatn scllatr uses ne Schmtt trgger capactr and resstr [-]. The crcut dagram vltage cntrlled relaxatn scllatr wth utput buer s shwn n Fg.. The utput requency vs. supply vltage (wth xed V = [V]) s shwn n Fg.. The utput requency vs. nput vltage (wth xed V = [V]) s dsplayed n Fg.. The dependence utput requency vs. supply vltage can be used r lnearzatn utput requency versus nput vltage (r current). The crcut dagram lnearzed, relaxatn scllatr wth utput buer s shwn n Fg. 9 []. Lnearzatn s based n supply vltage ncreasng tgether wth nput vltage. The s used as pwer surce r V. V. The supply vltage s gven by eq. (): V ss. V <. = V V. [V] () Output requency vs. nput vltage the lnearzed scllatr s dsplayed n Fg... Snusdal - Wen-brdge scllatr The vltage (current) cntrlled Wen-brdge scllatr [, ] s shwn n Fg. The peratnal ampler s used t rm vltage cntrlled current surce. The current, lw thrugh ddes and the and. The utput current s V = [A, V, Ω] () R where V s nput vltage and R resstr cnnected t nvertng nput. The Wen-brdge scllatrs cnssts, where ; R A ; R B are n pstve eedback. The buer and dde brdge, R, R, R and are used r autmatc gan (ampltude) cntrl [9]. The utput requency s gven as π R R = [Hz, F, Ω] () A B +. V Resstance s apprxmately V R k k k R V / R V = = [A, V, Ω] (9) V R I Fg. 9. The crcut dagram lnearzed, relaxatn scllatr wth utput buer. R =k; = pf;, -TL; I - 9,, - Schttky ddes, - ptcally cupled phtresstrs VTL where k s cnstant and d s current thrugh LE dde. nsderatn the R A =R B =R the utput requency s = V π R R = πr πr k [Hz, F, Ω] () A B Measured utput requency vs. nput vltage s shwn n Fg.. The requency spectrum s shwn n Fg. (spectral qualty s better than db). V R R R A R R R [MH z] y =.*x -. R B R R R 9 V [V] Fg.. Output requency vs. nput vltage r lnearzed relaxatn scllatr (see Fg. ). Measured values sld lne, apprxmatn dash lne Fg.. The Vltage cntrlled Wen-brdge scllatr wth buer ampler. R =k; =n; R =k; R =k; R =k; R =k; R =R =k; -TL; - x Schttky ddes, - ptcally cupled phtresstrs VTL 9

4 [khz] V [V] Fg.. Output requency vs. nput vltage r Wen-brdge scllatr Where R kω MΩ and N s value three dvder settngs. Pn shuld be ted t GN r the settng, the hghest requency range. Flatng Pn dvdes the master scllatr by. Pn shuld be ted t V+ r the settng, the lwest requency range. I ON + V M GN LT99 + V OPEN Fg.. nnectn current cntrlled scllatr LT99 The scllatr may be prgrammed by any methd that surces a current nt the pn (Pn ). The crcut n Fg. sets the scllatr requency usng a prgrammable current surce and n the expressn r OS, the resstr R s replaced by the rat.v/i ON. The vltage derence between V+ and s apprxmately.v, therere, the Fg. crcut s less accurate than a resstr cntrls the scllatr requency. Fg.. The requency spectrum vltage cntrlled Wenbrdge scllatr R + V M GN LT99 + V OPEN Fg.. The basc cnnectn scllatr LT99. Wde range square wave scllatr In ths part the wde range resstr set scllatr LT99 s descrbed []. The LT99 perates wth a sngle.v t.v pwer supply and prvdes a ral-t-ral, % duty cycle square wave utput. The requency-settng resstr can vary rm kω t MΩ t select a master scllatr requency between khz and MHz (V supply), see Fg.. The three-state nput determnes whether the master clck s dvded by, r bere drvng the utput, prvdng three requency ranges spannng khz t MHz (V supply). The scllatr requency s prgrammed by a sngle external resstr (R ) accrdng = NR [Hz, Ω] () N + V + M k R GN LT99 + V OPEN Fg.. nnectn vltage cntrlled scllatr LT99 Fg. shws the LT99 cngured as a VO. A vltage surce s cnnected n seres wth an external k resstr. The utput requency,, wll vary wth N, that s the vltage surce cnnected between V+ and the pn. Agan, ths crcut decuples the relatnshp between the nput current and the vltage between V+ and ; the requency accuracy wll be degraded. The scllatr requency, hwever, wll mntncally ncrease wth decreasng N.. nclusn In ths paper the several wde range smple scllatrs were descrbed. Fr requency cntrl, the ptcally cupled phtresstr was used. The square wave utput, rng, relaxatn and lnearzed relaxatn scllatr were descrbed. The Wenbrdge scllatr wth snusdal utput wth spectral qualty greater then db was als shwn. On the end, the wde range, square wave scllatr wth dvder was presented. All scllatrs were tested and measured. It s mprtant t nte that these scllatrs can be used n derent applcatn ncludng PLL, requency lcked lp and lw cst requency syntheszers. 9

5 . Acknwgledment Ths wrk was supprted by the Eurpean Regnal evelpment Fund and the Mnstry Educatn, Yuth and Sprts the zech Republc under the Regnal Innvatn entre r Electrcal Engneerng (RIE), prject N. Z../../.9 and by the Internal Grant Agency Unversty West Bhema n Plsen, the prject SGS-- and partly als by ree samples I's rm Lnear Technlgy.. Reerences [] J. unlp,. G. Smth, Telecmmuncatns Engneerng, rd ed. R Press, 99. [] W. Tmas, W. Electrnc mmuncatns System, New Jersey:, Prentce-Hall Inc., 99. [] Anrtsu Emea Lmted: MGA vectr sgnal generatr datasheet, Avalable at: anrtsu.cm/les/ MEGA_El.pd. [] A. L, "Prgrammable Oscllatr Uses gtal Ptentmeters," Analg evces, AN-, Avalable n: applcatn-ntes/an.pd [] Oscllatr cntrlled by dgtal ptentmeter, Avalable n: Hme/ - scllatr-cntrlled-by-dgtal-ptentmeter [] R. Marstn, "Understandng And Usng OTA OP-Amps," May, avalable n: uplads/magazne_dwnlads//may%%ray% Marstn%-%Understandng%And%Usng %OTA%OP-Amps.pd [] LM ual Operatnal Transcnductance Amplers wth Lnearzng des and Buers, Avalable n: [] VTL,, Lw st Axal Vactrls, PerknElmer Optelectrncs, Avalable n: cm/pt [9] T. Wegandt, K. Bemsup and P. R. Gray, Analyss Tmng Jtter n MOS Rng Oscllatrs,, n Prc. IEEE Int. Symp. rcuts and Systems, vlume, pp., Lndn, UK, June 99. [] Accurate and Ecent Frequency Evaluatn a Rng Oscllatr, Applcatn Nte -, Aglent Technlges [] M. Strk, "Vltage ntrlled Oscllatrs - snusdal and square wave rng and relaxatn scllatrs," Prceedngs the rd Medterranean nerence n Embedded mputng MEO - Budva, Mntenegr, ISBN: , OI:.9/MEO..9 [] W. Jaka, P. Prmmee, Electrncally Tunable urrentmde Multphase Snusdal Oscllatr Emplyng TA-based Allpass Flters wth Only Grunded Passve Elements, Radengneerng, Vl., NO., pp. 9-99, September [] P.S. Lnsay and.l. Wang, "Fast numercal ntegratn relaxatn scllatr netwrks based n sngular lmt slutns," IEEE Trans. Neural Net., 9: -, 99 [] T. Wegandt, K. Bemsup and P. R. Gray, Analyss Tmng Jtter n MOS Rng Oscllatrs,, n Prc. IEEE Int. Symp. rcuts and Systems, vlume, pp., Lndn, UK, June 99. [] Accurate and Ecent Frequency Evaluatn a Rng Oscllatr, Applcatn Nte -, Aglent Technlges. [] M. Strk, "Wde Range Vltage ntrlled Oscllatrs Snusdal Wen-brdge and Rng," Prceedngs the th Internatnal nerence Radelektrnka, ISBN: , OI:.9/Radelek..9, //$., IEEE [] R. Mancn and R. Palmer, Sne-Wave Oscllatr, Applcatn Reprt SL - March, Texas Instruments [] E. Lndberg, Oscllatrs An Apprach r a Better Understandng, Prceedngs the Eurpean nerence n rcut Thery and esgn, Krakw, Pland,. [9] M. Strk, "Snusdal and square wave vltage cntrlled scllatrs," Prceedngs the Internatnal nerence ELEKTRO,, Rajecke Teplce, ISBN: , OI:.9/ELEKTRO..9 [] LT99, khz t MHz, Resstr Set SOT- Oscllatr, Lnear Technlgy, Avalable n: 9