SCALOR BASED TUNABLE HIGH-PASS SALLEN-KEY FILTER

Transcription

1 BULETINUL INSTITUTULUI POLITEHNI DIN IAŞI Publict de Univeritte Tehnică Gheorghe Achi din Işi Tomul LVII LXI Fc. 4 0 SecŃi ELETOTEHNIĂ. ENEGETIĂ. ELETONIĂ SALO BASED TUNABLE HIGH-PASS SALLEN-KEY FILTE BY PAVEL BÎNZOI * AADIE AAN nd NIOLAE OJAN Jr. Gheorghe Achi Technicl Univerity of Işi Fculty of Electronic Telecommuniction nd Informtion Technology eceived June 5 0 Accepted for publiction: Augut 6 0 Abtrct. Thi pper preent the tuning performnce of econd order high-p Sllen-Key filter uing n x-controlled clor tht imulte grounded electriclly controlled reitnce. The imultion hve been mde uing trnitor level implementtion of current controlled current clor where the control prmeter i I x. Therefore for vrition of I x within the intervl [56 µa; 00 µa] the filter centrl frequency vrie from 6 khz to 435 khz. Key word: x-controlled clor; Sllen-Key filter tuning; MOS circuit.. Introduction In recent yer filter tuning technique hve received coniderble ttention from integrted circuit deigner. Mny technique for both centrl frequency tuning nd qulity fctor tuning Liu & Krilyn 00; Go & Snelgrove 998 hve been reported in the literture. The tunble element cn be cpcitor Schumnn & Tn 989 trnconductnce mplifier Krummencher & Joehl 988 MOS reitive circuit O et l. 00 etc. Thi pper exploit the poibility of uing n x-controlled clor Gorş 979 for ω c -tuning nd Q-tuning in Sllen-Key filter. * orreponding uthor: e-mil: pbrinzoi@etti.tuii.ro

2 58 Pvel Brînzoi Arcdie rcn nd Nicole ojn Jr. In pper publihed by Brînzoi & Gorş 0 technique of obtining electriclly controlled impednce uing current-controlled current clor h been reported. The ued cheme llow only the control of grounded pive element. Therefore thi ide cn be ued only for filter which contin grounded element. In thi ce ince the tructure of the x-controlled clor llow to implement only ingle-ended vrible pive element frequency tuning nd qulity fctor tuning for the preented filter cnnot be mde independently. Even though econd-order high-p Sllen-Key h been nlyed; thi technique cn be pplied to other type of filter well.. Sllen-Key Second-Order High-P Filter The Sllen-Key filter Deliynni 999 i populr ctive filter which cn be ued to crete econd order filter tge tht cn be ccded together to form higher order filter. The op-mp provide buffering between filter tge o tht ech tge cn be deigned independently from the other. Thi pper i focued on ingle tge deign employing n x-controlled clor for ω c -tuning nd Q-tuning. The chemtic for high p unity gin Sllen-Key filter i given in Fig.. Fig. HP Sllen-Key filter. The trnfer function for thi circuit i H = the centrl frequency being ω c = nd the qulity fctor

3 For = = Bul. Int. Polit. Işi t. LVII LXI f Q= 3. ω c = 4 nd Q=. 5 From 4 nd 5 one cn oberve tht for tuning ω c nd Q one cn ue or but only i grounded. We chooe to be relized the input reitnce of n x-controlled clor loded with fixed reitor. The principle of the cling technique i hown in Fig.. Fig. cling method. The input reitnce of thi circuit i = 6 k eq x where i the lod nd x will be current I x. 3. urrent-ontrolled urrent Sclor Nonidelitie For the trnitor level implementtion reported by Brînzoi & Gorş 0 mcromodel h been relized. It i repreented in Fig. 3 nd the component vlue re =0.54 pf 7

4 60 Pvel Brînzoi Arcdie rcn nd Nicole ojn Jr. = I x in µa GΩ 8 r = 4. Ω. 9 One cn oberve tht the component depend on the control current I x. Fig. 3 urrent-controlled current clor mcromodel. The expreion of the input impednce i. eq r I k Z x = 0 eplcing 0 in one obtin the following filter trnfer function: 0 H = where the denomintor coefficient re = I k r x = 3. 0 I k r x = 4

5 Bul. Int. Polit. Işi t. LVII LXI f One cn oberve tht the nonidelitie of the implemented currentcontrolled current clor do not chnge the filter order. Although it lter both the centrl frequency nd qulity fctor follow: k I x ' r ω c = 5 Q ' k I x r =. 6 [ k I x ] r In order to determine the centrl frequency nd the qulity fctor devition from their vlue given in nd 3 one define the reltive error for both prmeter follow: ' ωc ωc ω c er = 00 [%] 7 ω ' c Q Q Q er = 00 [%]. 8 Q 4. Deign Exmple The circuit in Fig. with the mcromodel in Fig. 3 w reported by Brînzoi & Gorş 0 which deign implementtion hve given. It h 6 MHz bndwidth o tht f c le thn 60 khz h been choen. In our ce f c = 00 khz. Since the number of unknown prmeter i lrger thn the number of eqution ome component will hve to be elected freely. If we chooe = = = 0 pf the reitor vlue will be follow: =.54 kω 9

6 6 Pvel Brînzoi Arcdie rcn nd Nicole ojn Jr. = 5.08 kω. 0 The vlue of the reitnce in Fig. 3 i of 5 kω. In order to obtin the vlue given in 0 for Z eq vlue of I x = 5.8 µa for the control current i needed. Uing thee vlue in the reltion 7 nd 8 one obtin w cer 0.50% Q er 0.308%. 5. Simultion The mll-ignl repone of the circuit propoed h been obtined by imultion. The performnce of the trnitor level implementtion of the tunble reitor i compred to the ce when mcromodel or n idel reitor Fig. 4 Filter repone mgnitude. Fig. 5 Filter repone phe. i ued. All the other component in the imulted circuit re idel. The opertionl mplifier i implemented voltge controlled voltge ource with gin of The mgnitude nd phe repone of the high-p Sllen- Key filter for the three ce re illutrted in Fig. 4 nd 5 repectively.

7 Bul. Int. Polit. Işi t. LVII LXI f In Fig. 6 nd 7 mgnitude nd phe repone of the deigned filter for different vlue of the control current I x re given. For thee imultion the trnitor level implementtion of the current-controlled current clor w ued. We hve found tht when the control current I x vrie from 56 µa to 00 µa centrl frequency vrie from 6 khz to 435 khz. Fig. 6 el filter chrcteritic mgnitude. Fig. 7 el filter chrcteritic phe. 6. oncluion A econd order tunble high-p Sllen-Key filter h been preented. It ue current-controlled current clor trnitor level implementtion. The circuit deign h been imulted in UM 0.8 µm technology nd powered t.8 V. The x-controlled clor ued for the implementtion of the tunble reitnce i limited to ingle-ended opertion which retrict the choice of

8 64 Pvel Brînzoi Arcdie rcn nd Nicole ojn Jr. tunble element to ingle-ended one. In thi ce it i not poible to chieve independent centrl frequency/qulity fctor tunning for the preented filter. Acknowledgment. The pper w relized with the upport ofe BAIN Doctorl Scholrhip n Invetment in Intelligence project finnced by the Europen Socil Found nd omnin Government. EFEENES Brînzoi P. Gorş L. Sclor Bed Electriclly ontrolled Impednce. Internt. Symp. on Sign. irc.. Syt. June 30 July Jy 0. Deliynni T.L. ontinuou-time Active Filter Deign. Pre LL Boc ton 999. Go W. Snelgrove W.M. A Liner Integrted L Bndp Filter with Q- Enhncement IEEE Trn. on irc.. Syt. II: Anlog. Digitl Sign. Proc Gorş L. The x-ontrolled Sclor nd It Appliction to Network Synthei IEEE Trn. on irc.. Syt. AS Krummencher F. Joehl N. A 4-MHz MOS ontinuou-time Filter with On-hip Automtic Tuning. IFEE J. of Solid-Stte irc Liu H. Krilyn A.I. A High Frequency Bndp ontinuou-time Filter with Automtic Frequency nd Q-Fctor Tuning. IEEE. Internt. Symp. on irc.. Syt. My 00 Jy I O J.I. rloen A. López-Mrtín A.J. MOSFET- Filter With On-hip Tuning nd Wide Progrmming nge. IEEE Trn. on irc.. Syt. II: Anlog. Digitl Sign. Proc Schumnn. Tn M.A. The Problem of On-hip Automtic Tuning in ontinuou- Time Integrted Filter. IEEE. Internt. Symp. on irc.. Syt. My 989 Jy I FILTU DE TIP SALLEN-KEY TEE-SUS EGLABIL U AJUTOUL SALOULUI ezumt Se prezintă un filtru Sllen-Key trece-u reglbil. FrecvenŃ centrlă cetui filtru ete vrită cu jutorul unei rezitenńe reglbile implementtă foloind un clor de curent comndt în curent. Proiectre filtrului ete înońită de un exemplu numeric ir pentru vlorile obńinute în urm cetui -u efectut imulări în vedere confirmării metodei propue de reglre frecvenńei centrle. Simulările u fot făcute utilizând o implementre l nivel de trnzitor cloruului de curent comndt în curent unde mărime de comndă ete curentul I x. Atfel pentru o vrińie curentului de control în intervlul [56 µa; 00 µa] frecvenń vriză de l 6 khz l 435 khz. De emene ete reprezentt grfic răpunul filtrului pentru trei czuri în cre rezitenń reglbilă ete reliztă utilizând o implementre MOS clorului x-comndt un mcromodel l clorului şi repectiv o rezitenńă idelă.