A 5th order video band elliptic filter topology using OTRA based Fleischer Tow Biquad with MOS-C Realization

Transcription

1 Natural ad Egieerig Scieces 44 olume 1, No. 2, 44-52, 2016 A 5th order video bad elliptic filter topology usig OTA based Fleischer Tow Biquad with MOS-C ealiatio Ahmet Gökçe 1*, Uğur Çam 2 1 Faculty of Electrical ad Electroics, Departmet of Electrical ad Electroics Egieerig, Uiversity of Iskederu Techical, Iskederu, Hatay, Turkey 2 Departmet of Electrical ad Electroics Egieerig, Faculty of Egieerig, Doku Eylül Uiversity, İmir, Turkey Abstract A ew 5th order video bad elliptic filter topology is preseted. I video applicatios high order elliptic filters were used. The proposed 5th order lowpass filter was simulated with PSPICE simulatio program. The elliptic filter cofiguratio cosists of two cascade coected lowpass otch filters ad a lowpass filter which is obtaied usig Operatioal Trasresistace Amplifier (OTA) based Fleischer Tow biquad. After desigig the 5th order video bad elliptic filter topology, the MOS-C realiatio is obtaied ad used i PSPICE simulatio. Keywords: Operatioal Trasresistace Amplifier, ideo filter applicatios, High order elliptic filters Article history: eceived 27 March 2016, Accepted 04 May 2016, Available olie 10 May 2016 Itroductio Active filters employig sigle active elemet are especially useful for applicatios where the power cosumptio is a importat desig costrait. Several voltage mode filters that use a active elemet rather tha operatioal amplifier have bee developed (Horg et al., 1997; Liu ad Lee, 1996; Salama ad Solima, 2000; Liu et al., 1993; Liu ad Tsao, 1991) to 1 * Correspodig Author :Ahmet Gökçe, ahmetgkc@gmail.com

2 Natural ad Egieerig Scieces 45 overcome well-kow op-amp limitatios such as costat gai-badwidth product, low slew rate, etc. The iterally grouded ad curret differecig iput termials of OTA make MOS-C realiatio possible. I other words, the resistors coected to the iput termials of OTA ca easily be implemeted usig MOS trasistors with complete oliearity cacellatio (Salama ad Solima, 1999). The resultig circuit will cosist of oly MOS trasistors ad capacitors. This will save a sigificat amout of chip area ad lead to circuits that are electroically tuable. That is, the resistace values ad hece the related filter parameters ca be adjusted by simply chagig the bias (gate) voltages. A literature survey shows that both Kerwi-Huelsma-Newcomb (KHN) ad Tow-Thomas (TT) biquads have bee implemeted usig curret coveyors, OTAs, ad OTAs (Kerwi et al.,1967; Thomas, 1968; Seai ad Sigh, 1995; Solima, 1994; Shah ad Bhaskar, 2002; Solima, 2007; Solima, 2008; Koto et al., 2010.) However, the Fleischer-Tow biquad, which is a improved versio of the Tow-Thomas cofiguratio, offers the realiatio of all 5 differet secod-order filterig fuctios, amely low-pass, high-pass, bad-pass, otch, ad all-pass (Gökçe et al., 2010). I this study, a OTA-based Fleischer-Tow biquad, which uses 2 capacitors, is preseted for the realiatio of 5th order video bad elliptic filter. Therefore, the realied filter is caoical i the umber of capacitors ad occupy less area o the chip. Additioally, the resoat frequecy ad quality factor of the filters ca be cotrolled idepedetly. All of the resistors used i the filters were realied by MOS trasistors. The resultat MOS-C implemetatio of the OTA-based Fleischer-Tow biquad is suitable for full itegratio. Operatioal Trasresistace Amplifier OTA is a high gai curret iput, voltage output device. The circuit symbol of the OTA is illustrated i Figure 1. p p OTA Figure 1 Circuit symbol of the OTA

3 Natural ad Egieerig Scieces 46 The operatio of the OTA ca be characteried by the followig equatios; p m ( I p 0 I ). (1) The OTA, which is kow also as curret differecig amplifier or Norto amplifier, is a importat active elemet i aalog ICs ad systems. Both iput ad output termials of OTA are characteried by low impedace, thereby elimiatig respose limitatios icurred by capacitive time costats. Sice the iput termials of OTA are at groud potetial, most effects of parasitic capacitaces ad resistaces disappear. The output termial of OTA exhibits low impedace so that OTA based voltage mode circuits ca easily be cascaded without additioal buffers. For ideal operatio, the trasresistace m approaches ifiity forcig the iput currets to be equal. Thus, the OTA must be used i a feedback cofiguratio i a way that is similar to the classical op-amp (Salama ad Solima, 1999). OTA has the advatages of high slew rate ad wide badwidth due to the fact that it beefits from the curret processig capabilities at the iput termials. O the other had, sice its output termial is characteried as low impedace, OTA is suitable for voltage mode operatios keepig the compatibility with existig sigal processig circuits (Salama ad Solima, 1999). 3 1 C 1 8 C 2 o p + + p p i Figure 2 OTA-C based realiatio of the Fleischer-Tow Biquad

4 Natural ad Egieerig Scieces 47 The OTA-C based realiatio of the Fleischer-Tow Biquad is show i Figure 2 (Gökçe et al., 2007; Gökçe ad Çam 2009). outie aalysis yields the trasfer fuctio as; o i 8 6 s 2 1 1C s C s C1C 1 8 s C C (2) With proper selectio of admittaces i Equatio (2), voltage mode secod order lowpass (LP), highpass (HP), badpass (BP) ad otch filters ca be realied(gökçe, 2010). MOS-C ealiatio The OTA is suitable for oliearity cacellatio, as the two iput termials are virtually grouded. Assume that the two NMOS trasistors, M1 ad M2, show i Figure 3, are matched ad operatig i the triode regio. Sice the trasistors M1 ad M2 have equal drai ad source voltages, both eve ad odd oliearities are cacelled (Salama ad Solima, 1999). Note that the equivalet resistace value, which appears betwee egative iput termial ad output termial of OTA, is give as 1 C ox W L a b, (3) where a ad b are the gate voltages. a i p + i M 1 M 2 I 1 I 2 p + b Figure 3 ealiig the resistor coected to the iput termial of OTA with MOS trasistors

5 Natural ad Egieerig Scieces 48 ideo Filter Applicatio The elliptic filter cofiguratio cosists of two cascade coected lowpass otch filters ad a lowpass filter which are obtaied usig OTA based Fleischer Tow biquad by proper selectio of resistors. After desigig the 5th order video bad elliptic filter topology, the MOS-C realiatio is obtaied ad used i PSPICE simulatio. Block diagram of the 5th order elliptic video filter is give i Figure 4. IN The Secod Order LP NOTCH Filter The Secod Order LP NOTCH Filter The First Order LP Filter Figure 4 Block diagram of proposed fifth order video filter OUT By replacig each resistor i Figure 2 with the MOS implemetatio of Figure 3, the fully itegrated realiatio of Fleischer-Tow biquad show i Figure 5 has bee obtaied. The resistor values ca be calculated by usig Equatio (3). It is easy to show that each resistor i Figure 3 ca be electroically cotrolled with a exteral voltage. Thus, the quality factor ca be adjusted electroically without disturbig the resoat frequecy with a exteral cotrol voltage (Gökçe, 2010). The MOS-C realiatio of the OTA based Fleischer Tow biquad topology is show i Figure 5.

6 Natural ad Egieerig Scieces 49 b 3 Mb 3 b 1 b 8 o b 4 Mb 1 b 7 Mb 8 b 2 Mb 4 Ma 4 P Mb 7 P Mb 2 P Ma 7 Ma 2 C 1 C 2 a 4 Ma 1 b 6 a 7 Ma 8 a 2 b 5 a 1 Mb 6 a 8 Mb 5 Ma 6 Ma 5 i a 6 Ma 3 a 5 a 3 Figure 5 MOS-C realiatio of the OTA based Fleischer Tow biquad The first order lowpass filter topology is also show i Figure C C 100 i 200 OTA o p Figure 6 oltage mode first order Lowpass filter

7 Natural ad Egieerig Scieces 50 Simulatio esults ideo filter is desiged to pass the sigals of frequecies up to 5 MH ad sharply suppress the sigals beyod this frequecy. Figure 8. CMOS realiatio of OTA (Salama ad Solima, 1999) To verify the theoretical study, filter was simulated with the PSPICE simulatio program. I the simulatios, a CMOS realiatio of OTA (Salama ad Solima, 1999), which is show i Figure 8, was used with the same trasistor aspect ratios as i (Salama ad Solima, 1999). Supply voltages were take as DD = 2.5 ad SS = 2.5. I the simulatio, 0.35 m TSMC techology parameters were used. Accordig to this parameter set, gate oxide thickess is give as Tox = m. Sice the oxide dielectric costat is ox = F/m, oxide capacitace is foud as Cox = ox / Tox = F. Electro mobility, was cm2 /.s for TSMC 0.35 m techology. The resistors are implemeted via MOS trasistors as metioed above. The resistor values correspod to 1=35kΩ, 2=25kΩ, 3=5kΩ, 4=20kΩ, 5=5kΩ, 6=5kΩ, 7=5kΩ, 8=5kΩ, C 1=4.5pF, C 2=4.5pF (for the first lowpass otch); 10=5.2kΩ, 20=10kΩ, 30=10kΩ, 40=5.2kΩ, 50=4.8kΩ, 60=5kΩ, 70=5kΩ, 80=5kΩ, C 10=4.5pF, C 20=4.5pF (for the secod lowpass otch); 200=2.6kΩ, 300=2.4kΩ, C 100=21pF (for the last lowpass)(gökçe, 2010). The simulated output voltage of the 5th order elliptic lowpass filter is show i Figure 9.

8 Natural ad Egieerig Scieces 51 Figure 9 Gai respose of the proposed filter The time step respose of the proposed video filter topology is show i Figure m 400m 0-400m -800m 0s 1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms (U10:OUT) Time Figure 10 Time step respose of the proposed filter efereces Fleischer, P.E., Tow, J., Desig formulas for biquad active filters usig three operatioal amplifiers, Proceedigs of the IEEE, Proceedig Letters, ol. 61, pp , Gökçe, A., Kılıç, S., & Çam, U Tek OTA Kullaılarak Tümlestirmeye Uygu İkici Derece Aalog Sügeç Tasarımları. IEEE 15th Sigal Processig ad Commuicatios Applicatios Coferece (SIU2007), Eskisehir / Turkey, Jue 2007.

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