CMOS Implementation of Lossy Integrator using Current Mirrors Rishu Jain 1, Manveen Singh Chadha 2 1, 2

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1 Proceedngs of Natonal Conference on Recent Advances n Electroncs and Communcaton Engneerng CMOS Implementaton of Lossy Integrator usng Current Mrrors Rshu Jan, Manveen Sngh Chadha 2, 2 Department of Electroncs and Communcaton Engneerng I.T.S Engneerng College, Plot No. 46, KP-III, Greater Noda-236(U.P.)-INDIA. rshu_jan@ts.edu.n manveenchadha@ts.edu.n 2 Abstract: - Analogue desgn can be consdered as a desgn procedure both n voltage-mode and current-mode form of sgnal processng. In lterature wde varety of technques and crcuts are avalable for the desgn of dfferent current-mode sgnal processng crcuts sutable for VLSI mplementaton. In ths paper we are presentng the CMOS mplementaton of current ntegrators (lossy type). All the proposed crcuts presented n ths paper were tested n SPICE usng.5µm CMOS process parameters provded by MOSIS (Aglent) and the results thus obtaned were n accordance wth the theoretcal values. Keywords: - Complementary CMOS current-mrrors, current-mode ntegrators, actve flters, analogue crcut desgn. I. INTRODUCTION Desgn of analogue ntegrated crcuts s recevng tremendous attenton n the feld of development and applcaton of current-mode processng, whch s rapdly domnatng tradtonal voltage-mode desgns. Currentmode technque for sgnal processng has receved consderable attenton, because t offers several advantages: () Hgher slew rates () Lower power consumpton () Hgher frequency range of operaton (v) Better accuracy and (v) Improved lnearty, over voltage-mode technques. [], [2], [8], [] and [6]. Also, currentmode sgnal processng s a very attractve approach due to the smplcty n mplementng operatons such as addton/subtracton, multplcaton by a constant, and the potental to operate at hgher sgnal bandwdths than ther voltage-mode analogues. Varous approaches wdely nvestgated are current-mode buldng blocks based current-mode crcuts; Gm-C based current-mode crcuts, swtched capactor and swtched current crcuts, Current-mode translnear and Log-doman crcuts. All of these approaches can be employed to devse fully ntegrable mplementaton n BPOLAR, CMOS, and BCMOS technology. Although BJTs and FETs are both current output devces often the transstors are assembled nto voltage orented crcuts and systems. A key performance feature of current-mode processng s nherent wde bandwdth capablty, and n a current amplfer the transstor s useful almost up to ts unty-gan bandwdth (f T ). Recent advances n IC technologes have meant that state-of-the-art analogue IC desgn s now able to explot the potental of current-mode analogue sgnal processng, provdng attractve and elegant solutons for many crcuts and system problems. Interest n current-mode (CM) flters has been growng due to the fact that current-mode devces have wder dynamc range, mproved lnearty, and extended bandwdth compared wth voltage-mode devces []. The commonly used crcut technques for desgnng current-mode flters are manly classfed nto two categores. () One technque s based on the transformaton of the voltage-mode crcuts to current-mode ones, such as the adjont network [2], the RC: CR dual transformaton [5] and the nverse-complementary network etc. () The other technque uses the drect current-mode ntegrators as the basc cell of the desgn bquad [2], [6], [9] and hgher-order flters. II. PROPOSED CIRCUITS Current-mode sgnal processng s qute attractve for low power supply voltage operaton and hgh frequency applcaton. In ths paper desgn of current-mode crcuts are presented usng nmos transstor current mrrors and pmos transstor current sources as actve loads. In these crcuts, pmos transstors are used for DC current sources whch provde bas currents to each current mrror and also behave as actve loads of the current mrror.

2 Proceedngs of Natonal Conference on Recent Advances n Electroncs and Communcaton Engneerng The currents of these sources must match each other and also match wth DC currents of each current mrror to gve a proper DC bas to transstors. However the matchng s sometmes dffcult due to the parameter msmatch between nmos and pmos transstors. A. Current Integrators usng Current Mrrors () Lossy Current Integrator (Non-Ideal Current Integrator): Fgure show a lossy current ntegrator whch conssts of an nmos and a pmos current mrror. +VDD IB M3 M4 I M M2 C Io Fg. : Lossy Current Integrator The gven crcut can easly be extended to a mult-nput and mult-output structure by addng nput current I I where sources parallel to and output transstors parallel to M 4. The output current s gven by s the nput sgnal current and t s assumed that (W/L) ratos are equal. Fgure 2 shows the small-sgnal equvalent crcut of the lossy current ntegrator shown n Fgure where R and R 3 are the small-sgnal equvalent resstances of M and M 3 respectvely. From Fgure 2, we can obtan the current transfer functon T I (s) as: T I s g g R R scr o m2 m4 3 where, g m2 and g m4 are respectvely the transconductance of transstors M 2 3 and M 4. R and R 3 are respectvely the nput resstances of transstors M and M 3. Thus, we can realze a lossy current ntegrator whch can be also be used as a frst-order flter secton. O B Fg. 2: AC Equvalent Crcut (Lossy Current Integrator) The transstors M and M 2 of the crcut shown n Fgure behaves as an nput buffer and n some applcatons where the nput buffer s not requred, ths secton can be removed thereby smplfyng the crcut as shown n Fgure 3. +VDD M M2 I IB C Io Fg. 3: Smplfed Lossy Current Integrator B. SIMULATION RESULTS The workablty of the proposed crcuts were tested and verfed n SPICE usng.5µm CMOS process parameters provded by MOSIS (AGILENT) as lsted n Table-. 2

3 Gan Gan Proceedngs of Natonal Conference on Recent Advances n Electroncs and Communcaton Engneerng TRANSISTOR nmos pmos TABLE-: CMOS PROCESS PARAMETERS PROCESS PARAMETERS LEVEL=3 UO=46.5 TOX=.E-8 TPG= VTO=.62 JS=.8E-6 XJ=.5U RS=47 RSH=2.73 LD=.4U VMAX=3E3 NSUB=.7E7 PB=.76 ETA=. THETA=.29 PHI=.95 GAMMA=.69 KAPPA=. CJ=76.4E-5 MJ=.357 CJSW=5.68E- MJSW=.32 CGSO=.38E- CGDO=.38E- CGBO=3.45E- KF=3.7E-28 AF= WD=.U DELTA=.42 NFS=.2E LEVEL=3 UO= TOX=.E-8 TPG= VTO=.58 JS=.38E-6 XJ=.U RS=886 RSH=.8 LD=.3U VMAX=3E3 NSUB=2.8E7 PB=.9 ETA=. THETA=.2 PHI=.95 GAMMA=.76 KAPPA=2 CJ=85E-5 MJ=.429 CJSW=4.67E- MJSW=.63 CGSO=.38E- CGDO=.38E- CGBO=3.45E- KF=.8E-29 AF= WD=.4U DELTA=.8 NFS=.52E [] Lossy Current Integrator: For the crcut shown n Fgure the ac analyss were carred out wth the value of dc bas current I B = 5µA, C = pf, (W/L) rato = µm/µm and supply voltage V DD = 2.5V. The value of cut-off frequency was found to be f O = MHz whch was very well n agreement wth the calculated theoretcal value of f O = 3.5MHz. SPICE smulaton results are shown n Fgure-4. Fgure-5 shows the change n the value of cut-off frequency wth change n the value of capactor..9 C=pF Fg. 4: Frst order Low Pass Response of Lossy Current Integrator.9.8 C=pF C2=2pF C3=5pF C4=pF C5=2pF Fg. 5: Varaton n cut-off frequency of Lossy Current Integrator wth capactor [2] Smplfed Lossy Current Integrator: For the crcut shown n Fgure 3 the ac analyss were carred out wth the value of dc bas current I B = 4µA, C = pf, (W/L) rato = µm/µm and supply voltage V DD = 2.5V. The value of cut-off frequency was found to be f O = 4.445MHz whch was very well n agreement wth the calculated theoretcal value of f O = 4.5MHz. 3

4 Current (A) Gan Proceedngs of Natonal Conference on Recent Advances n Electroncs and Communcaton Engneerng SPICE smulaton results are shown n Fgure-6. Fgure-7 shows the output of the crcut for a square nput of ampltude 5µA peak value and a perod of µs Fg. 6: Frst order Low Pass Response of Smplfed Lossy Current Integrator x -5 - Input Output Tme (sec) x -5 Fg. 7 Response of Smplfed Lossy Current Integrator for Square nput C. CONCLUSIONS In the gven paper current ntegrators lossy type have been presented whch can be used to form actve flters. These actve flters are qute sutable for the realzaton n hgh frequences of more than MHz. and these flters can operate at a voltage as low as.5v or less. The frequency of these flters can be easly and wdely controlled by a sngle DC bas current and ths provdes good tunablty. All the crcuts were tested usng SPICE and the verfed results confrms the theoretcal values. V. REFERENCES [] J. C. Ahn, and N. Fuj, Current-mode contnuous-tme flters usng complementary current mrror pars, IEICE Trans Fundamentals, vol. E79-A, no.2, pp.68-75, 996. [2] R. Angulo, M. Robnson, and E. S. Snenco, Current-mode contnuous-tme flters: two desgn approaches, IEEE Tran. On Crcuts and Systems, vol. 39, no. 5, pp , 992. [3] R. W. J. Barker, Accuracy of current mrrors, IEE Colloquum on Current-mode Analogue Crcuts, London, vol.25, paper 2, 989. [4] B. Glbert Wdeband negatve-current mrror, Electron Lett., vol., pp , 975. [5] J. B. Hughes, N. C. Brd, and I. C. Macbeth, Swtched-current: a new technque for analogue sampled-data sgnal processng, IEEE Proc. ISCAS 89, pp , 989. [6] J. B. Hughes, I. C. Macbeth, and D. M. Pattullo, Second generaton swtched-current sgnal processng, IEEE Intl. Symposum on Crcuts and Systems, 99. [7] D. G. Hag, and J. T. Taylor, Contnuous-tme and swtched capactor monolthc flters based on current and charge smulaton, IEEE Internatonal Symposum on Crcuts and Systems, Portland, USA, vol.3, pp , 989. [8] S. S. Lee, R. H. Zele, D. J. Allstot, and G. Lang, A contnuous-tme current-mode ntegrator, IEEE Trans. On Crcuts and Systems, vol.39, pp , 99. 4

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