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Int. J. Electron. Commun. (AEÜ) 62 (2008) 316–319

www.elsevier.de/aeue

LETTER

Electronicallytunableversatilevoltage-modeuniversalfilter

Hua-Pin Chen∗, Sung-Shiou Shen, Jenn-Pyng Wang

Department of Electronic Engineering, De-Lin Institute of Technology, Taiwan, ROC

Received 30 January 2007; accepted 29 April 2007

Abstract

A novel electronically tunable versatile voltage-mode universal biquad filter by using two single-output-operational

transconductance amplifiers (OTAs), one differential difference current conveyor (DDCC) and two capacitors is proposed.

The proposed circuit, which can be used as either a four-input single-output universal filter or a single-input three-output

multifunction filter with the same topology. Besides, the new circuit offers the following advantageous features: realization

of all the non-inverting and inverting biquadratic filter signals from the same configuration, no need to employ inverting-type

input signals, no need to component-matching conditions and low passive sensitivity performance.

? 2007 Elsevier GmbH. All rights reserved.

Keywords: Active filters; Voltage-mode circuits; Current conveyers

1. Introduction

Many current-mode and voltage-mode universal bi-

quadratic filter circuits employing operational transconduc-

tance amplifiers (OTAs) had been reported in the literature

[1–7]. These designs of OTA-C filter circuits require no

resistors. Therefore, they are suitable for monolithic inte-

gration than the other current conveyors. Moreover, an OTA

provides a highly linear electronic tunability and a wide

tunable range of its transconductance gain. Therefore, the

filters based on OTAs are the attention for many researches.

Recently, the use of differential difference current convey-

ors (DDCCs) in filters design has received considerable

attention because it can utilize the addition and subtraction

operators at the port X terminal [9–15]. In 2003, Horng

[8] proposed a high-input impedance voltage-mode univer-

sal biquadratic filter with three inputs and single output

∗Corresponding author. Tel.: +886222733567x388.

E-mail addresses: hpchen@dlit.edu.tw (H.-P. Chen), shen@dlit.edu.tw

(S.-S. Shen), jpwang@dlit.edu.tw (J.-P. Wang).

1434-8411/$-see front matter ? 2007 Elsevier GmbH. All rights reserved.

doi:10.1016/j.aeue.2007.04.008

employing two multiple current output OTAs, one plus-

type second-generation current conveyor and two floating

capacitors. It needed an inverting-type voltage input signal

to realize the allpass (AP) filter response. In 2005, Nisar

et al. [16] proposed a versatile voltage-mode universal filter

with three inputs and three outputs employing three current

feedback amplifiers, three resistors and two capacitors. The

proposed circuit is capable of implementing as many as 18

filtering functions, but needed component-matching con-

ditions to realize some filtering functions. Recently, Shah

and Malik [17] proposed a voltage-mode bandstop (BS),

bandpass (BP) and lowpass (LP) filters employing two four-

terminal floating nullors, one OTA, two grounded capacitors

and two resistors. However, this circuit needs employing

external passive resistors to realize the same voltage-mode

multifunction filter. In this paper, the authors present a new

versatile universal voltage-mode filter with four inputs and

three outputs employing two OTAs, one DDCC and two ca-

pacitors. The proposed configuration can act as a multifunc-

tion voltage-mode filter with single input and three outputs,

and can simultaneously realize voltage-mode LP, BP and BS

filter signals from the three output terminals, respectively,

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H.-P. Chen et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 316–319 317

without any component-matching constraints. On the other

hand, it also can act as a universal voltage-mode filter with

four inputs and single output and can realize all the non-

inverting and inverting biquadratic filter signals from the

same configuration without any inverting voltage input sig-

nals. The proposed filter does not employ external resistors

thus is an active-C filter. This is unlike biquads reported in

[17], which needs employing external passive resistors to re-

alize the same voltage-mode multifunction filter. Moreover,

the proposed circuit is capable of implementing as many

as 18 filtering function without any component-matching

conditions. This is unlike biquads reported in [16], which

needs component-matching conditions to realize some fil-

tering functions.

2. Circuit description

The operational transconductance amplifier is a differen-

tial voltage-controlled current source with transconductance

gain gm, which can be characterized by the port relations

with Io= gm(V+− V−) [1]. The positive DDCC can be

characterized by the port relations with IY1=IY2=IY3=0,

VX=VY1−VY2+VY3and IZ+=+IX[15]. The proposed

circuit, as shown in Fig. 1, employs two OTAs, one DDCC

and two capacitors. After routine analysis of this circuit, its

output transfer functions can be derived as

Vo1=1

?[(sC2gm1)Vi1+ (s2C1C2)Vi2

− (sC2gm1)Vi3+ (gm1gm2)Vi4],

Vo2=1

+ sC2gm1)Vi3− (sC1gm2+ gm1gm2)Vi4],

(1)

?[(gm1gm2)Vi1+ (sC1gm2)Vi2+ (s2C1C2

(2)

+

+

gm1

gm2

Vi4

Vi3

Vo3

Vo1

Vo2

Vi2

Vi1

C2

C1

Y1

Y2

Y3

Z+

X

Fig. 1. The proposed four-input three-output voltage-mode univer-

sal filter.

Vo3=1

?[(s2C1C2+ gm1gm2)Vi1− (s2C1C2)Vi2

+ (sC2gm1)Vi3− (gm1gm2)Vi4],

where ? = s2C1C2+ sC2gm1+ gm1gm2.

Depending on the status of the biquad input four voltages:

Vi1, Vi2, Vi3and Vi4, numerous filter functions are obtained.

There are two cases for examples shown as follows.

Case I: If Vi1= Vin(the input voltage signal) and Vi2=

Vi3=Vi4=0 (namely,thecapacitorC1andC2aregrounded),

then

(3)

Vo1

Vin

Vo2

Vin

Vo3

Vin

=

sC2gm1

s2C1C2+ sC2gm1+ gm1gm2,

gm1gm2

s2C1C2+ sC2gm1+ gm1gm2,

s2C1C2+ gm1gm2

s2C1C2+ sC2gm1+ gm1gm2.

Thus, the non-inverting BP, non-inverting LP and non-

inverting BS filters are obtained at the node voltages, Vo1,

Vo2and Vo3, respectively. Note that the input signal, Vi1=

Vin, is connected to the high-input impedance input node of

the DDCC (the Y1port of the DDCC). So the circuit en-

joys the advantage of having high-input impedance, lead-

ing to cascadability at the input port. Also, the use of only

grounded capacitors is particularly attractive for integrated

circuit implementation.

Case II: The specialization of the numerators in Eqs. (1)

and (3) result in the following five generic filter functions:

(4)

=

(5)

=

(6)

(i) if Vi1= Vi2= Vi3= 0 and Vi4= Vin, the non-inverting

and inverting LP filters can be obtained at Vo1and Vo3,

simultaneously.

(ii) if Vi1= Vi2= Vi4= 0 and Vi3= Vin, the non-inverting

and inverting BP filters can be obtained at Vo1and Vo3,

simultaneously.

(iii) if Vi1= Vi3= Vi4= 0 and Vi2= Vin, the non-inverting

and inverting highpass (HP) filters can be obtained at

Vo1and Vo3, simultaneously.

(iv) if Vi1= Vi3= 0 and Vi2= Vi4= Vin, the non-inverting

and inverting BS filters can be obtained at Vo1and Vo3,

simultaneously.

(v) if Vi1= 0 and Vi2= Vi3= Vi4= Vin, the non-inverting

and inverting AP filters can be obtained at Vo1and Vo3,

simultaneously.

Obviously, from cases I to II, the proposed circuit can act

as a multifunction voltage-mode filter with single input and

three outputs and it can also act as a universal voltage-mode

filter with four inputs and a single output, too. Therefore, the

proposed circuit is more versatile than those with a single

input and three outputs or with multiple inputs and a single

output [6–8,17]. Furthermore, the proposed configuration is

capable of implementing as many as 18 filtering functions

with suitable choice of inputs and outputs as depicted in

tabular form in Table 1.

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318H.-P. Chen et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 316–319

Table 1. Choice of inputs and outputs to implement different

filtering functions

Inputs OutputFiltering function

Vi1

Vi2

Vi3

Vi4

0

1

0

0

1

1

0

0

1

0

0

0

1

0

0

1

0

0

0

0

1

0

1

0

0

1

0

0

1

1

0

1

1

0

1

1

0

0

0

0

0

0

1

0

0

1

0

0

0

0

0

0

1

1

1

0

1

1

0

0

0

0

1

0

0

0

1

1

1

0

1

1

Vo1

Vo2

Vo2

Vo3

Vo3

Vo1

Vo1

Vo2

Vo2

Vo3

Vo1

Vo3

Vo3

Vo1

Vo3

Vo3

Vo1

Vo3

Non-inverting LP

Non-inverting LP

Non-inverting LP

Inverting LP

Non-inverting LP

Non-inverting BP

Inverting BP

Non-inverting BP

Inverting BP

Non-inverting BP

Non-inverting HP

Inverting HP

Non-inverting HP

Non-inverting BS

Inverting BS

Non-inverting BS

Non-inverting AP

Inverting AP

In all cases, the resonance angular frequency ?oand qual-

ity factor Q are given by

?

?o=

?gm1gm2

The low passive sensitivities of ?oand quality factor Q

are shown as follows:

C1C2

,Q =

C1gm2

C2gm1. (7)

S?o

gm1= S?o

SQ

gm2=1

gm2=1

2,S?o

C1= S?o

SQ

C2= −1

gm1= −1

2,

2.

C1= SQ

By taking into account the non-idealities of the DDCC,

the relationship of the terminal voltages and currents can be

rewrittenasVX=?1VY1−?2VY2+?3VY3andIZ+=?IX[10].

The transconductance gain gmi of the OTA with the non-

idealities can be assumed as gmi=gmi?gi/s+?gi?gmi(1−

?is), where ?gi is the first-order pole of the OTA and

?i=1/?gi[18]. The denominator of the transfer function of

Fig. 1 becomes

?

+ sC2gm1?2

2,

C2= SQ

D(s) = s2C1C2

1 −C2gm1?2?1− gm1gm2?1?2

C1C2

?

Due to the parasitic effect, the characteristic departs from

the ideal response. But, the parasitic effect can be made

negligible by satisfying the following conditions:

?

1 −gm2(?1+ ?2)

C2?2

?

+ gm1gm2. (8)

C2gm1?2?1− gm1gm2?1?2

C1C2

>1,

gm2(?1+ ?2)

C2?2

>1. (9)

3. Conclusion

A new versatile universal voltage-mode filter with four

inputs and three outputs has been presented. The proposed

circuit can be acted as both a multifunction voltage-mode

filter with a single input and three outputs and a universal

voltage-mode filter with four inputs and a single output.

Therefore, the voltage-mode filter proposed in this paper is

more versatile than the universal one with a single input and

three outputs or the universal one with multiple inputs and a

single output. The proposed configuration does not employ

external resistors thus is an active-C filter. Moreover, the

new circuit still offers the following advantages: (i) no need

to component-matching conditions, (ii) no need to employ

inverting-typeinputsignalsand(iii)allthenon-invertingand

inverting standard filter functions can be obtained without

changing circuit topology.

Acknowledgments

The authors are thankful to the anonymous reviewers for

useful suggestions on the earlier version of this paper that

improved the paper quality.

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Hua-Pin Chen was born in Taipei, Tai-

wan, Republic of China, in 1966. He

received the M.S. and Ph.D. degrees

from Chung Yuan Christian University,

Chung, Taiwan, in 2001 and 2005, re-

spectively. Since August 2005, he is af-

filiated asAssistant Professor in the De-

partment of Electronic Engineering at

the De-Lin Institute of Technology, Tai-

wan. His teaching and research interests

are in the areas of Circuits and Systems, Analog and Digital Elec-

tronics, Active Filter Design and Current-Mode Signal Processing.

Sung-Shiou Shen received M.S.E.E.

from the Department of Electronic

Engineering, National Taiwan Uni-

versity of Science and Technology,

in 1992. From 1992 to 1996, he was

worked on microwave transmitters and

receivers in Chung-Shan Institute of

Science andTechnology,

Taiwan. From 1997 to 2000, he was

with the Institute of Astronomy and

TaoYuan,

Astrophysics, Academia Sinica, Taipei, Taiwan, where he worked

on the development of sub-millimeter astronomical telescopes.

Since 2000, he has been a lecturer at the Department of Electronic

Engineering, Delin Institute of Technology in Taiwan.

Jenn-Pyng Wang received his degree

of Ph.D. from Department of Physics,

University of Cincinnati, Ohio, USA,

in 1995. Then, he joined the Industrial

Technology and Research Institute of

Taiwan working in the field of the me-

chanical integrity. Five years later, he

switched to the industrial specialized in

the SMT and LCD tiling processes. In

2003, he became an assistant professor

of the Department of Electronic Engineering, Delin Institute of

Technology in Taiwan.