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Dual Input All-Pass Networks Using MO-OTA and its Application Pipat Prommee1, Krit Angkeaw2, Jirasak Chanwutitum2, and Kobchai Dejhan1 Faculty of Engineering and Research Center for Communication and Information Technology King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand Tel: +66-2326-4238, +66-2326-4242, Fax: +66-2326-4554 2 Industrial Electrical Technology Department, Faculty of Engineering King Mongkut’s Institute of Technology North Bangkok, Bangkok 10800, Thailand Email: [email protected] 1 Abstract— This paper presents a realization of grounded passive elements first order all-pass networks using a multiple-output operational transconductance amplifier (MO-OTA) and three grounded passive elements. The proposed circuit is operated in current-mode for the good benefit as well as high output impedance and cascadability. Therefore, it can be directly employed as a subsystem of monolithic circuit without additional matching circuits. Furthermore, a new quadrature oscillator is presented as an application for confirmed the theory and realistic practically. The PSpice simulation results verifying of theoretical are also included. I. INTRODUCTION Current mode signal processing circuits have recently demonstrated many advantages over their voltage mode counterparts including increased bandwidth, higher dynamic range and better suitability for operation in reduced supply environment [1]. In many papers, current mode circuits are presented by using CCII based [2]-[4]. Unfortunately, CCII does not have a differential input. The OTA is a familiar device for voltage-mode and current-mode applications. The OTA provides a highly linear electronic tunability and a wide frequency range. Moreover, OTA-based circuits require no resistors and therefore, are suitable for monolithic implementation and small die area [5]-[6]. The MO-OTA has been proposed in previous paper [7]. From the strong points, due to many output of OTA, the MO-OTA has more flexible to use in term of a modern analog signal processing as well. The previously presented all-pass filter topologies employing conventional OPAMP [8-9] that ensure the low bandwidth and voltage-mode are achieved. The FTFN [10], Current Differencing Buffer Amplifier (CDBA) [11] and CCII [2]-[4] are also introduced but some of these reports suffer from floating passive components. The floating components are trade-off in the practical realizations, parasitic capacitances, bandwidth restrictions, complicated adjustment. The floating node passive devices have to avoid in the design for minimized the error reasons. This paper presents the design of all grounded passive elements all-pass network using one MO-OTA and three grounded passive elements. The presented topologies can be designed by using both in CMOS or bipolar technology. The circuits comprise phase lead and phase lag Moreover, current gain can be adjust by a transconductance (gm) through Iabc. The simple construction and low voltage are proposed that suitable for further IC fabrication. II. THEORY AND PRINCIPLE The OTA is a simple device that has been found in many recently reports. The benefit of OTA is a voltage and current mode realization can be done with a simple structure. The tunable characteristic is a strong excellent point for the future applications. The single output OTA is a conventional device that might be has some restrictions on the design. The modification of OTA can be eliminated that restrictions by extended the output port namely a multiple-output OTA (MOOTA). A. Multiple-output operational transconductance amplifier The OTA has input as voltage and current output. The simple structure of the well-known OTA, having used only four transistors and current source. Figure 1 shows the symbol of MO-OTA. The output current of MO-OTA yields I o # " g m (V! V ) (1) The transconductance gm is variable by bias current Iabc. Note that the transconductance base on CMOS and bipolar technology are equal to ($Iabc/4)1/2 and Iabc/2VT respectively. A possible implementation of OTA using multiple output operation transconductance amplifiers was proposed [12]. -Io -Io V- V+ +Io +Io Iabc Iabc Io V+ gm V- Fig.1. (a) CMOS MO-OTA structure and (b) symbol ECTI-CON 2007 The 2007 ECTI International Conference ___________________________________________________________ 129 -Io The transconductance of above CMOS OTA can be expressed as: gm # $I abc 4 # %COX WI abc (2) 4L The realization of the proposed all-pass network filter using OTA is show in Fig.2. The circuit comprises one MOOTA, 2 grounded resistors and a grounded capacitor. From this point of view, the proposed structure is simpler than the other existing all-pass realizations [2]-[4]. In Fig.2(a) and Fig.2(b), the all-pass transfer functions are realized as eq.3 and eq.4 respectively. The circuit model of a non-ideal OTA operating in saturation region is shown in figure 3, where Ci is the input capacitance, CO is the output capacitance and GO is the output conductance. Generally GO is less than gm. The proposed circuits in figure 2(a) and 2(b) can be express in term of high frequency as eq(8) and eq(9), respectively. Io V+ Ci gm(V+-V-) Co Go -Io VI1 0.5R R C +I2 gm I1 +I2 I1 -I2 I1 C 0.5R (a) (b) Fig.2. Proposed Allpass Filter Networks I2 + sCR 1 ( # "K) & I1 * sCR ! 1 ' I2 + 1 sCR ( # "K) & I1 * 1 ! sCR ' (3) Go gm R 2 1 RC Fig.3. Circuit model for non-ideal case of the MO-OTA + sR.C ! 2Ci / 1 ( I2 && # " K )) I1 * .sRC ! 1/.0.5sRCi ! 1/ ' (8) + 1 ! sR.C ! 2Ci / ( I2 && # " K )) I1 * .1 ! sRC /.1 ! 0.5sRCi / ' (9) (4) (5) III. QUADRATURE OSCILLATOR APPLICATION The quadrature oscillator based on all-pass network is shown in Fig. 4. The circuit consists of phase-lead and phaselag all-pass network configurations in Figs. 2(a) and (b). In Fig. 4, the circuit can be oscillated due to the loop-gain is unity, the transfer function can be expressed as From Eq.(3), the phase shift are varying between 180, to 0, while (4), the phase shift are varying between 0, to -180,. The pole frequency (-o) can be expressed as -o # Co From (8)-(9) imply that the parasitic capacitances affect to the poles and zeros of the transfer function at the high frequency. Gain (K) is a constant and defined as K# gm(V+-V-) gm -I2 R Ci + 1 sC2 R2 (+ sC1R1 1 ( &&)) && # 1 T1 ( s )T2 ( s ) # K1K 2 )) * 1 ! sC2 R2 '* sC1R1 ! 1 ' (10) (6) Where the constants are K1=gm1R1/2 and K2=gm2R2/2, loop-gain is unity independent with the any transconductances , gmi. The phase of first all-pass network is written as The passive sensitivities can be obtained as S R-O # SC-O # 1 (7) In Fig. 2, it can see that the output impedance of the circuit is very high due to the OTA current output; hence it can be directly interconnection with load or any current mode circuits without the buffer circuit. The output current gain can be adjusted by gm through the bias current Iabc. 1 (- ) # 2 tan 1 (-01 ) , 0 1 # C1R1 (11) Likewise, the phase of second all-pass network is 1 (- ) # 180 2 tan 1 (-0 2 ) , 0 2 # C2 R2 ECTI-CON 2007 The 2007 ECTI International Conference ___________________________________________________________ 130 (12) TABLE 1. PARAMETER USED IN SIMULATION The frequency of oscillation can be given as -# -# or R1 C1 1 0 10 2 1 0.5R2 (OTA)2 gm2 Iout1 R2 0.5R1 (13b) C1C 2 R1 R2 (OTA)1 gm1 (13a) Iout2 .MODEL NMOS LEVEL=3 UO=460.5 TOX=1.0E-8 TPG=1 VTO=+0.62 JS=1.08E-6 XJ=0.15U RS=417 RSH=2.73 LD=0.04U VMAX=130E3 NSUB=1.71E17 PB=0.761 ETA=0.00 THETA=0.129 PHI=0.905 GAMMA=0.69 KAPPA=0.10 CJ=76.4E-5 MJ=0.357 CJSW=5.68E-10 MJSW=0.302 CGSO=1.38E-10 CGDO=1.38E-10 CGBO=3.45E-10 KF=3.07E-28 AF=1 WD=+0.11U DELTA=+0.42 NFS=1.2E11 DELL=0U LIS=2 ISTMP=10 TT=0.1E-9 .MODEL PMOS LEVEL=3 UO=100 TOX=1.0E-8 TPG=1 VTO=0.58 JS=0.38E-6 XJ=0.10U RS=886 RSH=1.81 LD=0.03U VMAX=113E3 NSUB=2.08E17 PB=0.911 ETA=00 THETA=0.120 PHI=0.905 GAMMA=0.76 KAPPA=2 CJ=85E-5 MJ=0.429 CJSW=4.67E-10 MJSW=0.631 CGSO=1.38E-10 CGDO=1.38E-10 CGBO=3.45E-10 KF=1.08E-29 AF=1 WD=+0.14U DELTA=0.81 NFS=0.52E11 DELL=0U LIS=2 ISTMP=10 TT=0.1E-9 C2 Phase (deg) Gain (dB) Fig. 4. The quadrature oscillator using proposed all-pass networks From (13), the oscillation frequency is depended on passive elements, R1, R2, C1 and C2. The components are defined identically as R1=R2=R and C1=C2=C. The oscillation frequency is actually becomes -# 1 (14) CR IV. SIMULATION RESULTS In order to confirm the validity of the proposed circuits, PSpice simulation was carried out. The parameters used in simulation are 0.5µm CMOS model obtained through MIETEC as listed in table 1. The W/L parameters of MOS transistors are assumed of 20µm/1µm for NMOS and 60µm/1µm for PMOS. The supplied voltages are VDD = -VSS = 1.5 V. The corner frequency of 15.9 kHz are obtained with such passive elements setting as R=10k2 and C=10nF. The simulation results are illustrated for the current transfer function characteristic in Fig.6 (a) and Fig.6 (b). The characteristics represent for the phase response of phase-lead and phase-lag all-pass filter, respectively. It can be observed that the circuits provide a bandwidth for a several MHz. From Fig.6, the effective of parasitic capacitances at output of OTA are taken in order to the high frequency according to eq. (8) and (9). The application of proposed all-pass networks is a quadrature oscillator as shown in Fig.4. The simulation result of proposed oscillator application has shown in Fig. 7. The 2 outputs can be obtained for a quadrature behavior. The phase different is about 90, according with the theoretical. The waveform of the quadrature oscillator are in the assuming conditions, gm1=gm2=200µs, R1=R2=10k2 and C1=C2=0.01µF. The oscillation frequency can be obtained ensure that are in agreement with the above theoretical about 16 kHz. gain phase Fig .6 (a) The phase response of filter topology in Fig.2(a) Phase (deg) Gain (dB) gain phase Fig .6(b) The phase response of filter topology in Fig.2(b) ECTI-CON 2007 The 2007 ECTI International Conference ___________________________________________________________ 131 [10] M. Higashimura, “Current-mode allpass filter using FTFN with grounded capacitor,” Electron. Lett., vol. 27, pp. 1182-1183, 1991. [11] A. Toker, S. Ozoguz, O. Cicekoglu, and C. Acar, “Current-mode allpass filters using current differencing buffered amplifier and a new highQ bandpass filter configuration,” IEEE Trans. Circuits and Syst., II, vol. 47, pp. 949-954, 2000. [12] C.-C. Hsu and W.-S. Feng, “Structural design of current-mode biquad filters,” Int. J. Electron., vol. 88, pp. 41-51, 2001. [13] Z. Wang, “2-MOSFET transistors with extremely low distortion for output reaching supply voltage,” Electron. Lett., vol. 26, pp. 951-952, 1990. Iout1 Iout2 Fig. 7. Output waveform of quadrature oscillator in Fig. 4 V. CONCLUSION The dual input multiple-output OTA all-pass filter topologies with all grounded passive elements are presented. The phase-lead and phase-lag can be simply modification with a few passive components changed. The proposed topologies does not limit for the implementation in bipolar or CMOS technology. The proposed circuits tried to use the MOS transistors for OTA realization. The output current can be applied to next circuit without the any matching devices. The cascadable topology is a benefit of proposed current mode schemes. The cascade of proposed both types can be obtained a quadrature oscillator as an application. Due to the minimized component, decreasing components can be done by the electronic resistors [13] that implemented from only 2 MOS transistors. The oscillator will used only 2 capacitors for the passive elements. The filter and oscillator simulation results are obtained a good agreement with the theories suitable for further IC fabrication. [1] [2] [3] [4] [5] [6] [7] [8] [9] REFERENCES C. Toumazou, C. Lidgey, and D. G. Haigh, Analogue IC design: the current mode approach, Peter peregrinus ltd., 1990. M. Higashimura and Y. Fukui, “Realization of current mode all-pass networks using a current conveyor,” IEEE Trans. Circuits and Syst., vol. 37, pp. 660-661, 1990. A. M. Soliman, “Generation of current conveyor based all-pass filters from op-amp based circuits,” IEEE Trans. Circuits and Syst., II, vol. 44, pp. 324-330, 1997. O. Cicekoglu, H. Kuntman, and S. Berk, “All-pass using a single current conveyor,” Int. J. Electron., vol. 86, pp. 947-955, 1999. E. Sanchez-Sinencio, J. Ramirez-Angulo, B. Linares-Barranco, and A. Rodriguez-Vazquez, “Operational transconductance amplifier-based nonlinear function syntheses,” IEEE J. Solid-State Circuit, vol. 24, no. 6, pp. 1576-1586, 1989. A. Rodriguez-Vazquez, B. Linares-Barranco, J. L. Huertas, and E. Sanchez-Sinencio “On the design of voltage-controlled sinusoidal oscillators using OTAs,” IEEE Trans. Circuits and Syst., vol. 37, pp. 197-211, 1990. J. Ramirez-Angulo, and E. Sanchez-Sinencio, “High-frequency compensated current-mode ladder filter using multiple output OTAs,” IEEE Trans. Circuits and Syst., II, vol. 49, pp. 581-586, 1994. J. V. Vosper, “Synthesis of first-order active-R allpass networks and their application in sinusoidal oscillator design,” Electron. Lett., vol. 27, pp. 53-55, 1991. R. Holzel, “A simple wide-band sine wave quadrature oscillator,” IEEE Trans. Instrum. Meas., vol. 42, pp. 758-760, 1993. ECTI-CON 2007 The 2007 ECTI International Conference ___________________________________________________________ 132