Electronically tunable current-mode biquad filter employing CCCDTAs and grounded capacitors with low input and high output impedance

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Electronically tunable current-mode biquad filter employing CCCDTAs and grounded capacitors with low input and high output impedance

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Q1

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Winai Jaikla a,∗ , Fabian Khateb b , Surapong Siripongdee a , Piya Supavarasuwat a , Peerawut Suwanjan a a Department of Electrical Communication Engineering, Faculty of Industrial Education, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand b Department of Microelectronics, Brno University of Technology, Technická 10, Brno, Czech Republic

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a r t i c l e

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i n f o

a b s t r a c t

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Article history: Received 18 April 2013 Accepted 31 May 2013

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Keywords: Current-mode CCCDTA Filter Integrated circuit Analog circuit

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1. Introduction

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In this study, a single-input multiple-outputs current-mode analog biquadratic filter, based on current controlled current differencing transconductance amplifier (CCCDTA) is presented. The proposed filter uses two CCCDTAs and two grounded capacitors without any external resistors, which is well suited for integrated circuit implementation. The filter simultaneously gives 3 standard transfer functions, namely, lowpass, highpass and bandpass filters with independent control of quality factor and pole frequency by electronic method. By summing of IHP and LLP , the notch filter can be also achieved. Moreover, the circuit has low input and high output impedance which would be an ideal choice for cascading in current-mode circuit. The PSPICE simulation results are included verifying the workability of the proposed filter. The given results agree well with the theoretical anticipation. © 2013 Elsevier GmbH. All rights reserved.

Over the past few years, a number of schemes based on current-mode circuit have been developed. It is stated that the current-mode circuits give the potential advantages such as inherently wide bandwidth, higher slew-rate, greater linearity, wider dynamic range, simpler circuitry and lower power consumption [1,2] which is found that number of papers have been published dealing with the implementation of current-mode circuits [3–5]. An analog active filter is one of the standard research topics in current-mode circuit design. This circuit is one of the important requirements in electrical and electronic applications, widely used for continuous-time analog signal processing. It is generally used in many fields, such as communications, measurement, and instrumentation, and control systems [6,7]. Especially, the filters which provide several functions in the same topology, namely, universal filter or multifunction filter, have been receiving considerable attention. If the number of input and output signal in filter is considered, the universal filters can be categorized into three types: a single-input, multiple-output (SIMO) type [2], a multiple-input, single-output

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

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∗ Corresponding author. Tel.: +66 813051643. E-mail addresses: [email protected], [email protected] (W. Jaikla), [email protected] (F. Khateb), [email protected] (S. Siripongdee), [email protected] (P. Supavarasuwat), [email protected] (P. Suwanjan).

(MISO) type [8] and a multiple-input, multiple-output (MIMO) type [9]. One of the most popular analog filters is a single-input, multiple-output topology in which various transfer functions can be realized simultaneously. The SIMO topology can be found in many applications, for example in touch-tone telephone tone decoder, in phase-locked loop FM stereo demodulator, or in crossover network as a part of the three-way high-fidelity loudspeaker [3]. With growing interest in design of current-mode filters, more attention is being paid to the filters which have the highoutput impedance because they make them easy to drive loads and they facilitate cascading without using a buffering device [9,10]. Modern electronically controllable active building blocks (ABBs) provide the flexibility and enabling a variety of circuit designs in analog signal processing. These circuits can be easily controlled by microcomputer or microcontroller which has been considerable attention. Also some circuits which use active building block can avoid the use of the external resistors. This will reduce the cost and chip area. Biolek proposed the interesting active building block namely, current differencing transconductance amplifier (CDTA) [11]. The modification of CDTA is later introduced namely, current controlled current differencing transconductance amplifier (CCCDTA) [12], which parasitic resistances at input port can be electronically controlled. A new configuration capable of realizing current-mode lowpass, highpass, bandpass and notch filters with single input and multiple outputs using two CCCDTAs and two capacitors is presented in this paper. The quality factor and pole frequency can

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Please cite this article in press as: Jaikla W, et al. Electronically tunable current-mode biquad filter employing CCCDTAs and grounded capacitors with low input and high output impedance. Int J Electron Commun (AEÜ) (2013), http://dx.doi.org/10.1016/j.aeue.2013.05.014

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Fig. 3. Proposed SIMO current-mode filter.

is converted to the x-terminal current via a transconductance gm . The characteristics of CCCDTA can be described by:

⎡

Vp

⎤

⎡

Rp

⎢ ⎥ ⎢ Vn ⎥ ⎢ ⎢ ⎥ ⎢0 ⎢I ⎥ = ⎢ ⎣ z,zc ⎦ ⎣ 1

0

0

Rn

0

−1

0

0

Ix

⎤⎡ I ⎤ p 0 ⎢ ⎥ ⎥ I 0 ⎥⎢ n ⎥ ⎥ ⎥⎢ ⎢ ⎥ 0 ⎦ ⎣ Vx ⎦

0 ±gm

0

(1)

Rp = Rn =

VT 2IB1

(2)

and 68 69 70 71 72 73 74 75

be independently adjusted with electronic method. The proposed filter has low input and high output impedance providing easy current-mode cascading. The paper is organized as follows. In Section 2, the characteristics of CCCDTA and proposed filter with either an ideal or a non-ideal active element are presented. The simulation results and their evaluations are given in detail in Section 3. The comparison with previous filter using CDTA and CCCDTA is described in Section 4. Finally, Section 5 concludes the paper.

gm =

2. Principle of operation

77

2.1. CCCDTA overview

78

IB2 2VT

(3)

Here VT is the thermal voltage. IB1 and IB2 are the bias currents used to control the intrinsic resistances and transconductance, respectively. The internal construction of BJT CCCDTA is shown in Fig. 2.

79 80 81 82 83

The proposed second-order current-mode filter is illustrated in Fig. 3. It consists of two CCCDTAs and two grounded capacitors. The parasitic resistances Rp1 and Rn1 of CCCDTA1 are controlled by bias current IB1 . IB2 is used to control gm1 of CCCDTA1 . The second parasitic resistances (Rp2 and Rn2 ) and gm2 of CCCDTA2 are tuned by IB3 and IB4 , respectively. It is obvious that the proposed filter provides simultaneously three frequency responses (HP, LP and BP) with high output impedance property. Moreover, the low input impedance of the proposed filter can be achieved by setting IB1 as high as possible. It is also found in Fig. 3 that the proposed filter uses the same type of CCCDTA without the plus and minus types of output terminals. This will be economical on the numbers of transistors

The principle of CCCDTA was introduced in [12]. Its symbol and equivalent circuit are shown respectively in Fig. 1(a) and (b). The p and n which have finite resistances (Rp and Rn ) are the current input terminals. z, zc (z-copy) and x are the output terminals. The difference of input currents (ip − in ) will send to z terminal. The current at z terminal is copied to zc terminal. The voltage at z terminal

Q17

Q18

Q19 Q14

Q13 p

IB1

Q9

Q20 Q21

n

Q10

Q15

Q22 Q Q 23 24

Q25

Q16

Q3

Q4

Q31

Q7

VCC

Q38 Q32 x

Q27

Q12 Q5 Q6

Q30

zc

z

Q28

Q2 Q1

Q29

Q26

Q11

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2.2. Proposed current-mode biquad filter

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85

Vz

If the CCCDTA is realized using BJT technology, Rp , Rn and gm can be written as

Fig. 1. CCCDTA (a) symbol (b) equivalent circuit.

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Q8

IB2

Q33 Q35

Q36

x

Q34 Q37

VEE

Fig. 2. Internal construction of CCCDTA.

Please cite this article in press as: Jaikla W, et al. Electronically tunable current-mode biquad filter employing CCCDTAs and grounded capacitors with low input and high output impedance. Int J Electron Commun (AEÜ) (2013), http://dx.doi.org/10.1016/j.aeue.2013.05.014

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in CCCDTA. Considering the ideal CCCDTA, a routine analysis of the proposed filter provides the following current transfer functions:

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IHP s2 = 2 Iin s + (sgm1 /C1 ) + (gm2 /C1 C2 Rp2 )

(4)

111

sgm1 /C1 IBP =− 2 Iin s + (sgm1 /C1 ) + (gm2 /C1 C2 Rp2 )

(5)

112

and

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gm2 /C1 C2 Rp2 ILP = 2 Iin s + (sgm1 /C1 ) + (gm2 /C1 C2 Rp2 )

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Fig. 4. Frequency responses of proposed filter.

(6)

Moreover, the notch response can be easily achieved by summing of IHP and ILP . This yields the current transfer function as s2 + (gm2 /C1 C2 Rp2 ) IBS = 2 Iin s + (sgm1 /C1 ) + (gm2 /C1 C2 Rp2 )

(7)

port. The influences of parasitic impedances of the x terminals of CCCDTA1 and CCCDTA2 are negligible because of their connection to low-impedance input n (CCCDTA1 ). The most important parasitic impedances are resistive and capacitive parts affecting the z and zc ports of CCCDTAs, acting in parallel to C1 and C2 . Let us denote them Rz1 , Cz1 , Rzc2 , Czc2 and Rz2 , Cz2 , respectively. Considering into these effects, the transfer functions will be modified to the more general forms:

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∗ IHP

Iin

˛p1 ˇ1 s2 + s[(˛p1 ˇ1 /C2∗ Rz2 ) + (˛p1 ˇ1 /C1∗ )((1/Rz1 ) + (1/RzC2 )) + (˛p1 ˇ1 /C1∗ Rp2 )(1 − ˛p2 ˇ2 )] + (˛p1 ˇ1 /C1∗ C2∗ Rz2 )((1/Rz1 ) + (1/RzC2 )) + (˛p1 ˇ1 /C1∗ C2∗ Rp2 Rz2 )(1 − ˛p2 ˇ2 )

=

s2 + s(ω0∗ /Q ∗ ) + ω0∗2

(15)

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118

The pole frequency (ω0 ) and quality factor (Q) of each filter response can be expressed to be

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ω0 =

120

and

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121

122



Q =

gm2 C1 C2 Rp2



1 gm1

C1 gm2 C2 Rp2

If Rpi = VT /2IBi and gmi = IBi /2 VT as written in Eqs. (2) and (3), the pole frequency and quality factor are written:

123

124

1 ω0 = VT

125

and

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Q =

2





IB2

Rp2



SIω0 = SIω0

132

and

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SIQ0 B2

B3

B4

(10)

C1 IB3 IB4 C2

=

=

=

SCQ0 1

1 1 = ; SCQ0 = − 2 2 2

(12)

(13)

2.3. Analysis of non-ideal case

136 137

Iz = ˛p Ip − ˛n In ; Izc = ˇIz

138 139

∗ ILP

153

=

(˛p1 ˛p2 gm2 /C1∗ C2∗ Rp2 ) s2 + s(ω0∗ /Q ∗ ) + ω0∗2

(17)

where C1∗ = C1 + Cz1 + CzC2 and C2∗ = C2 + Cz2 . In this case, the ω0 and Q are changed to



ω0∗ =

1 C1∗ C2∗ Rz2



1 − ˛p2 ˇ2 1 1 + + + ˛n1 gm1 Rz1 RzC2 Rp2



+

˛n1 ˛p2 gm2 C1∗ C2∗ Rp2

(18)

154

155 156

157

158

(19)

It should be mentioned that the stray/parasitic z-terminal capacitances are absorbed by the external grounded capacitors as they appear in shunt with them. However, the parasitic resistances Rz1 , Rzc2 and Rz2 not only affect the ω0 and Q by they also add parasitic zeros to the HP and BP transfer functions. The parameters ˛p , ˛n and ˇ of the CCCDTAs affect the gain of all the filter sections. 3. Simulation results

For non-ideal case, the CCCDTA can be respectively characterized with the following equations,

135

and

152

159

160 161 162 163 164 165

(11)

1 1 = ; SVω0 = −1; SCω0 = SCω0 = − T 1 2 2 2

SIQ0 B4

(16)

s2 + s(ω0∗ /Q ∗ ) + ω0∗2

and

IB3 IB4 C1 C2

−1; SIQ0 B3

˛p1 gm1 (s(1/C1∗ ) + (1/C1∗ C2∗ Rz2 ))

(C1∗ /C2∗ Rz2 )((1/Rz1 ) + (1/RzC2 ) + (1 − ˛p2 ˇ2 /Rp2 ) + ˛n1 gm1 ) + (˛n1 ˛p2 C1∗ gm2 /C2∗ Rp2 ) (C1∗ Rp2 /C2∗ Rz2 ) + ((Rp2 /Rz1 ) + (Rp2 /RzC2 ) + 1 − ˛p2 ˇ2 + ˛n1 gm1 Rp2 )

From Eqs. (10) and (11), it is found that the quality factor can be adjusted independently from the pole frequency by varying IB2 . Considering in Eqs. (10) and (11), the sensitivities of the proposed circuit can be found as

131

134

(9)

=

Iin

Iin

Q∗ =

126

(8)

∗ IBP

(14)

where ˛p and ˛n are the current error gains from p and n ports to z port. ˇ is the current error gain from z port to zc

The performances of proposed filter are verified using PSpice. The CCCDTA is realized as showed in Fig. 2. The PNP and NPN transistors employed in the proposed circuit were simulated by respectively using the parameters of the PR200N and NR200N bipolar transistors of ALA400 transistor array from AT&T [13]. The DC power supply voltages are ±3 V. The filter was designed with the following parameters of its components: C1 = C2 = 1 nF, Rload = 1 , IB1 = 150 ␮A, IB2 = 100 ␮A, IB3 = 50 ␮A and IB4 = 200 ␮A. The simulations yield the pole frequency of 562.34 kHz and the quality factor of 2, while the theoretical value of the pole frequency from Eq. (10) is 612.44 kHz (thus the deviation is 8.18%). This error is from the influences of current tracking errors of CCCDTA as analyzed in Eq. (18). The results shown in Fig. 4 are the gain responses of the proposed filter from Fig. 2. It is clearly seen that the filter can simultaneously provide low-pass, high-pass and band-pass functions without modifying the circuit topology. By summing of IHP and ILP , the notch response is achieved. The gain and phase responses of notch filter are illustrated in Fig. 5. The proposed filter was excited

Please cite this article in press as: Jaikla W, et al. Electronically tunable current-mode biquad filter employing CCCDTAs and grounded capacitors with low input and high output impedance. Int J Electron Commun (AEÜ) (2013), http://dx.doi.org/10.1016/j.aeue.2013.05.014

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4 Table 1

Q4 Comparison between various current-mode filters using family of CDTA. Ref

Filter category

ABB

No. of ABB

No. of R +C

Grounded capacitors only

Independent tune of Q and ω0

No requirement of plus and minus ABB

Low input impedance

High impedance for all output

[7] [14] [15] [16]

SIMO SIMO SIMO (Fig. 10) SIMO

CDTA CDTA CDTA CDTA

1 3 2 2

1+2 0+2 0+2 1+2

Yes Yes Yes Yes

No Yes No Yes

No Yes Yes Yes

No Yes Yes No

[17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] Proposed filter

SIMO MISO MISO SIMO SIMO MIMO SIMO SIMO MISO MISO MISO SIMO

CDTA CDTA CDTA ZC-CITA CDTA CDTA CDTA CDTA CDTA CDTA CCCDTA CCCDTA

2 3 2 2 1 1 2 1 4 2 1 2

0+2 0+2 0+2 0+2 1+2 1+2 0+2 2+2 2+2 0+2 0+2 0+2

Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes

No No No Yes (Fig. 3b) No (Fig. 3c) No No No No No No No No Yes No No Yes

No Yes Yes No No No No No Yes No No Yes

Yes Yes Yes Yes No Yes Yes No Yes Yes No Yes

No Yes Yes Yes No Yes No No Yes Yes Yes Yes

circuit in Fig. 2 is compared with several current-mode filters from [14–27]. The results are shown in Table 1. It can be seen that it matches all the criteria in the best way among all other filters. 5. Conclusions

Fig. 5. Gain and phase response of notch filter.

Fig. 6. Transient responses of proposed filter when Iin is 20 ␮A/545.75 kHz sinusoidal signal.

The current-mode biquad filter has been presented in this contribution. The advantages of the proposed circuit are that: (i) it performs low-pass, high-pass, and band-pass functions from the same simple circuit configuration; (ii) the quality factor and the pole frequency can be independently controlled by electronic method; (iii) the filter has low input and high output impedance; (iv) the circuit uses only two CCCDTAs, two grounded capacitors and no resistors, which is attractive for its IC implementation; (v) it uses the same type of active element without plus and minus output terminal which is economical on the numbers of transistor in CCCDTA. Acknowledgements The described research was performed in laboratories supported by the SIX project; the registration number CZ.1.05/2.1.00/03.0072, the operational program Research and Development for Innovation and has been supported by Czech Science Foundation as project No. GA102/11/1379. References

198 199 200

201

202 203 204 205 206 207 208 209 210 211 212

213

214 215 216 217 218

219

Fig. 7. Band-pass responses for different values of IB2 .

185 186 187 188 189 190 191 192 193

194 195

196 197

by 20 ␮A/545.75 kHz sinusoidal signal. The transient responses are shown in Fig. 6. The total harmonic distortions (THD) for IHP , IBP and ILP outputs are 0.736%, 0.274% and 0.665%, respectively. The magnitudes of simulated input and output impedance are as follows; Zin = 98.41 , ZHP = 261.69 k, ZBP = 1.48 M and ZLP = 258.58 k. Considering Eq. (11), the Q can be controlled by IB2 without affecting the ω0 . The Q tuning is confirmed via the BP response in Fig. 7. By varying IB2 with different values of 50 ␮A, 100 ␮A and 200 ␮A, the quality factors are 4, 2 and 1, respectively. 4. Comparison with previous current-mode filters using CDTA or CCCDTA Literature survey shows that a lot of papers dealing with current-mode filter using family of CDTA [14–27]. The proposed

[1] Toumazou C, Lidgey FJ, Haigh DG. Analogue IC design the current-mode approach. London: Peter Peregrinus; 1990. [2] Minaei S. Electronically tunable current-mode universal biquad filter using dual-X current conveyors. J Circ Syst Comput (JCSC) 2009;18:665–80. [3] Ibrahim MA, Minaei S, Kuntman H. A 22 5 MHz current-mode KHN-biquad using differential voltage current conveyor and grounded passive elements. AEU – Int J Electron Commun 2005;59:311–8. [4] Minaei S, Cicekoglu O, Kuntman H, Dündar G, Cerid O. New realizations of current-mode and voltage-mode multifunction filters without external passive elements. AEU – Int J Electron Commun 2003;57:921–7. [5] Biolek D, Lahiri A, Jaikla W, Siripruchyanun M, Bajer J. Realization of electronically tunable voltage-mode/current-mode quadrature sinusoidal oscillator using ZC-CG-CDBA. Microelectron J 2011;42:1116–23. [6] Sedra AS, Smith KC. Microelectronic circuits. 3rd ed. Holt, FL: Rinehart and Winston; 1991. [7] Biolek D, Biolkova V, Kolka Z. Current-mode biquad employing single CDTA. Indian J Pure Appl Phys 2009;47:535–7. [8] Horng J-W. Current-mode universal biqudaratic filter with five inputs and one output using tree ICCIIs. Indian J Pure Appl Phys 2011;49:214–7. [9] Horng J-W. High output impedance current-mode universal biquadratic filters with five inputs using multi-output CCIIs. Microelectron J 2011;42:693–700.

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[10] Soliman AM. New current mode filters using current conveyors. Int J Electron Commun (AEU) 1997;51:275–8. [11] Biolek D. CDTA – building block for current-mode analog signal processing. In: Proceedings of the European Conference on Circuit Theory and Design 2003 – ECCTD’03. 2003. p. 397–400. [12] Siripruchyanun M, Jaikla W. CMOS current-controlled current differencing transconductance amplifier and applications to analog signal processing. Int J Electron Commun (AEU) 2008;62:277–87. [13] Frey DR. Log-domain filtering: an approach to current-mode filtering. IEE ProcG Circ Syst Dev 1993;140:406–16. [14] Biolek D, Biolkova V. CDTA-C current-mode universal 2nd-order filter. In: Proceedings of the 5th WSEAS International Conference on Applied Informatics and Communications. 2005. p. 411–4. [15] Biolek D, Senani R, Biolkova V, Kolka Z. Active elements for analog signal processing: classification, review, and new proposals. Radioengineering 2008;17:15–32. [16] Biolek D, Biolková V. Universal biquads using CDTA elements for cascade filter design. Contribution to the book “Computational Methods in Circuits and Systems Applications” WSEAS Press Electrical and Computer Engineering Series; 2003p. 232–236. [17] Keskin AU, Biolek D, Hancioglu E, Biolkova V. Current-mode KHN filter employing current differencing transconductance amplifiers. Int J Electron Commun (AEÜ) 2006;60:443–6. [18] Tangsrirat W. Cascadable current-controlled current-mode universal filters using CDTAs and grounded capacitors. J Active Passive Electron Dev 2009;4:135–45.

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[19] Tangsrirat W, Dumawipata T, Surakampontorn W. Multiple-input singleoutput current-mode multifunction filter using current differencing transconductance amplifiers. Int J Electron Commun (AEU) 2007;61: 209–14. [20] Biolek D, Biolkova V, Kolka Z, Bajer J. Single-input multi-output resistorless current-mode biquad. In: Proc. of ECCTD ‘09, European Conference on Circuit Theory and Design. 2009. p. 225–8. [21] Shah NA, Munazah Q, Iqbal SZ. Realization of CDTA based current-mode universal filter. Indian J Pure Appl Phys 2008;46:283–5. [22] Biolek D, Biolková V, Kolka Z. Single-CDTA (current differencing transconductance amplifier) current-mode biquad revisited. WSEAS Trans Electron 2008;5:56–62. [23] Kacar F, Kuntman HH. A new, improved CMOS realization of CDTA and its filter applications. Turk J Electr Eng Comput Sci 2011;19:632–42. [24] Prasada D, Bhaskara DR, Singh AK. Universal current-mode biquad filter using dual output current differencing transconductance amplifier. Int J Electr Commun (AEU) 2009;63:497–501. [25] Kumngern M, Phatsornsiri P, Dejhan K. Four inputs and one output current-mode multifunction filter using CDTAs and all-grounded passive components. 10th International Conference on ICT and Knowledge Engineering 2012;5:9–62. [26] Jin J, Wang C. Current-mode universal filter and quadrature oscillator using Q3 CDTAs. Turk J Electr Eng Comput Sci 2013 (in press). [27] Siripruchayanun M, Jaikla W. Electronically controllable current-mode universal biquad filter using single DO-CCCDTA. Circ Syst Signal Process 2008;27:113–22.

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