Indian Journal of Pure & Alied Phyic ol. 4, etember 005,. 74-79 Oerational tranconductance amlifier baed voltage-mode univeral filter Naeem Ahmad & M R Khan Deartment of Electronic and Communication Engineering, Fo Engineering & Technology, Jamia Millia Ilamia, New Delhi 0 05 and Moinuddin Deartment of Electrical Engineering, Faculty of Engineering & Technology, Jamia Millia Ilamian New Delhi 0 05 Received 0 October 00; revied March 005; acceted June 005 An oerational tranconductance amlifier (OTA) baed voltage-mode univeral filter i reented. The rooed circuit emloy four OTA with two grounded caacitor and realize lowa, banda and higha filter function. The ole-frequency w and ole-, are orthogonally adjutable by roer choice of tranconductance gain of OTA and caacitor value. The rooed univeral filter can alo be ued for the realization of notch filter function. In addition a current feedback amlifier (CFA)-baed univeral filter i alo realized by converting the OTA-baed circuit uing tandard tranformation method [Hou C L & Wang W Y, IEE Proc Circuit Device and ytem, 44, 09-.]. Both the circuit have been tudied in detail. The imulation reult have alo been included. Keyword: Oerational tranconductance amlifier, Amlifier, Univeral filter, OTA, Current feedback amlifier, Tranconductance IPC Code: H0H Introduction An oerational tranconductance amlifier (OTA) i widely ued a an active element in analog ignal roceing circuit. It i a differential inut voltage controlled current ource (DC) device. The ort relation of OTA a hown in Fig. i ( + )g m I o () where, + i the differential inut voltage, I o i the OTA outut current and g m i the tranconductance gain of the oerational tranconductance amlifier determined by the relation g m (I B T ), where, I B i the bia current of OTA and T i the volt equivalent of temerature equal to 6 m at room temerature. OTA rovide linear variation of tranconductance gain g m over a fairly wide range and due to the deendence of g m on the bia current I B of OTA, circuit arameter of interet uch a ole frequency, quality factor in cae of filter and frequency of ocillation in cae of ocillator etc. can be electronically tuned. Alo due to the reence of tranconductance gain arameter g m, circuit realizing filter, ocillator and gyrator, etc. can be deigned in uch a way that they are free from aive reitor. Alo due to current ource at the outut of OTA, the frequency reone of OTA circuit i much better than o-am-baed circuit. Owing to their attractive feature dicued above, the tranconductance amlifier are widely ued in the realization of filter, inuoidal ocillator, grounded and floating inductor -6 and in non-linear circuit alication 7. OTA-C circuit enjoy eay IC imlementation ecially when all caacitor are grounded. Univeral filter find wide alication in the field of communication and intrumentation engineering, their utility increae when they are caable of roviding all the filter function imultaneouly for a ingle voltage or current ource without changing the baic tructure of the circuit. Many voltage-mode and Fig. Oerational tranconductance amlifier ymbol
AHMAD et al: OLTAGE-MODE UNIERAL FILTER 75 current-mode univeral filter are reorted in the literature 8-. The rooed circuit for the realization of univeral filter emloy only four OTA and two grounded caacitor a againt the circuit given elewhere and rovide lowa, banda and higha filter function imultaneouly for an analog inut ource. Notch filter can alo be obtained by umming u lowa and higha reone which require an additional OTA ummer hown in Fig.. By aroriate choice of tranconductance gain of variou OTA the ole-frequency and ole-, can be orthogonally tuned. The electronic tuning of both the arameter i inherent to the circuit. The comonent read i mall. The enitivity figure are fairly low. In the end OTA-baed univeral filter ha been converted into an equivalent current feedback amlifier (CFA)-baed univeral filter uing available tranformation technique. The imulation reult of both the filter circuit are included. Circuit Decrition and Analyi The circuit of OTA-baed univeral filter i deicted in Fig.. The imle circuit analyi uing OTA ort relation given in Eq. () yield the following voltage tranfer ratio' of the univeral filter. LP in BP in g g g CC g D() m m m4 m () ( g g ) C D() m m () HP ( gm gm) (4) D() in ( + ) (5) Notch LP HP in whetre Fig. Circuit for obtaining Notch filter reone D g C g g g CC g () + ( m ) + m m m4 m Fig. oltage-mode OTA-baed univeral filter.
76 INDIAN J PURE & APPL PHY, OL 4, EPTEMBER 005 The ole-frequency, and ole-, for the filter are given by g g g m m m4 (6) CC gm g g C m m4 (7) gmgmc ubtituting, g m g m4 g', g m g m g, and C C C (8) in Eq (6) and (7), The exreion for and modifie to, g C m (9) g m (0) gm Equation (9) and (0) exlain the oeration of the circuit for the condition deicted in Eq. (8). Firt the ole-frequency can be electronically tuned to the required value through g m and then ole-, can be adjuted through g m. On the other hand at any oint of time the quality factor of the filter can be varied electronically through g m without diturbing the etting of ole-frequency. Moreover, if we vary the ole frequency through a gang caacitor (which i oible only in dicrete circuit) then the tuning of and become comletely indeendent of each other. Other uitable rooition i to alway kee the ratio g m g m a contant value uch that whenever g m varie g m alo varie to kee the ratio of g m g m a contant that kee at a contant value. Thi rooition i good where we do not want to change the quality factor once it i fixed for ome value alo the temerature variation effect on the filter erformance are reduced. imulation of OTA-Univeral Filter Circuit The rooed univeral filter a hown in the Fig.. i imulated uing LM700 OTA model on Pice baed oftware for f 76. KHz and. The deigned element value were, C C 0nF, and I B I B I B I B4 50 μa. The frequency reone lot were obtained for notch filter and for lowa, banda and higha filter a hown in Fig. 4 and Fig. 5, reectively. The imulated reult are found to be cloe to thoe of theoretical value ecially for ole frequency f, wherea ole ha light deviation which can be afforded. The OTA voltage-mode univeral filter ha been tranformed into a current feedback amlifier (CFA) baed circuit uing the technique decribed Fig. 4 OTA Notch Filter
AHMAD et al: OLTAGE-MODE UNIERAL FILTER 77 elewhere. The tranformed CFA-baed univeral filter i hown in the Fig. 6 and it frequency reone curve are given in Fig 7 and 8, reectively. 4 CFA-Baed Active Univeral Filter The circuit obtained from rooed OTA-univeral filter through tranformation uing tranformation method i hown in Fig. 9. The voltage tranfer function of the CFA-univeral filter were obtained uing imle circuit analyi,and are given a follow Fig. 5 Frequency reone lot of voltage-mode univeral filter GGG CC G G C G G G C C G LP() 4 IN() + + 4 G G G C G G G C C G HP() IN() + + 4 G G C G G C G G G C C G BP() IN() + + 4 () () () Fig 6 CFA-baed voltage -mode univeral filter. From the above equation the ole-frequency w and ole- are given by GGG 4 (4) CCG GGC 4 (5) C G G
78 INDIAN J PURE & APPL PHY, OL 4, EPTEMBER 005 Fig. 7 Frequency reone lot of CFA univeral filter Fig. 8 Notch filter reone of CFA univeral filter
AHMAD et al: OLTAGE-MODE UNIERAL FILTER 79 where α i and β i are current and voltage tracking error of CFA for i,, and defined a I z αi x and o β z where α ε (ε <<) and β ε, (ε <<). It i oberved that the active and aive enitivity value are fairly low. Fig. 9 Circuit for obtaining Notch filter reone For C C C and G G 4 G and G G G, Eq (4) and (5) become (6a) CR R R (6b) Equation (6a) and (6b) how an attractive feature of thi circuit which i it linear relationhi of quality factor with reitor R and orthogonal adjutment of and. By imultaneouly varying R and R 4, w can be tuned. Wherea by imultaneouly varying R and R quality factor can be changed without diturbing the etting of w. 5 imulation Reult of CFA Univeral Filter The CFA-baed univeral filter obtained from OTA-CFA tranformation uing tranformation method i deigned for f 5.9 khz and i imulated uing AD844A on the Pice baed oftware TINA Pro. The element value were C C 0 nf, and R R R R 4 kω. The imulation reult are hown in Fig 7 and 8. 6 enitivity Figure The active and aive enitivity figure calculated for ole- and ole-frequency are given in Eq. (7) R, α, α, α, β, β, β C, C, R, R, R 4 R, α, α, α, β, β, β C, C, R, R, R 4 (7) 7 Concluion A new OTA-baed voltage-mode filter i realized. The rooed circuit ue only two grounded caacitor and a minimum of four ingle outut OTA and realize lowa, banda and higha filter function. The notch filter can alo be realized uing an OTA ummer. The w and can be indeendently tuned. In addition to the OTA univeral filter, a CFA univeral filter i alo obtained imly by converting the rooed OTA circuit into CFA-baed univeral filter uing tranformation method. The CFA circuit i alo imulated. The reult of both the circuit are found to be verifying the theoretical claim. The working of both the univeral filter i excellent. The enitivity figure are fairly low. Reference Hou C L & Wang W-Y, IEE Proc Circuit Device & ytem, 44 (year) 09. Malvar H, IEEE Tran, CA-9 (98). Ahmad N, Moinuddin & irothia K, Electronic Engineering, UK (997) 4 Ahmed N & hah N A, IETE, 6a (99). 5 hah N A & Ahmed N, Int J Electronic, 68 (990) 96. 6 Ahmad N, Electronic Engineering U K, (995) 8. 7 einencio E anchenz-angulo J Ramirez, Barranco B Linare & azquez A Rodriguez, IEEE J olid tate Circuit, C-4 (989) 576. 8 Geiger R L & Edgar anchez-inencio, IEEE Circuit & Device, Magazine,, Number (March, 985) 0 9 un Y & Fidler J K, Int J Electr, 8 (996) 95. 0 Horng G W, Weng R, Lee M H & Chang C W, Int J Electr, 8 (997) 4. Moniri M & Al-Hahimi B M, Int J Electr, 8 (997) 7. Dudek F, Hahimi Bahir Al & Moniri Manour, Int J Electr, 87 (000) 6.