Circuits and Systems, 2011, 2, 34-37
doi:10.4236/cs.2011.21006 Published Online January 2011 (http://www.SciRP.org/journal/cs)
Voltage-Mode Lowpass, Bandpass and Notch Filters Using
Three Plus-Type CCIIs
Jiun-Wei Horng, Zhao-Ren Wang, Chih-Cheng Liu
Department of Electronic Engineering, Chung Yuan Christian University, Chung-Li, Taiwan, China
Received November 3, 2010; revised November 15, 2010; accepted November 18, 2010
Abstract
A single input and three outputs voltage-mode biquadratic filter using three plus-type second-generation
current conveyors (CCII), two grounded capacitors and five resistors is presented. The proposed circuit of-
fers the following features: realization of three filter functions, which are, lowpass, bandpass and notch fil-
ters, simultaneously, the use of only grounded capacitors. PSPICE simulation results are also included.
Keywords: Active Filter, Current Conveyor, Voltage-Mode, Biquad
1. Introduction
There is a growing interest in designing active filters
using current conveyors. This is attributed to their high
signal bandwidths, greater linearity and larger dynamic
range [1,2]. The second-generation current conveyor
(CCII) proves to be a versatile building block that can be
used to implement a variety of high performance circuits,
which are simple to construct. The current-feedback am-
plifier (CFA) exhibits the potentiality of extended oper-
ating bandwidth and relatively large value of slew rate
compared to the conventional voltage-feedback amplifier.
Note that a CFA is equivalent to a plus-type CCII with a
voltage follower [3]. On the other hand, the use of only
plus-type CCII in filters design has received considerable
attention because of its simplicity [4-6].
The circuits consist of more filter functions mean mo-
re applications they can be used. Therefore, many cicuits
with one input terminal and multiple output terminals
were presented [7-11]. In 1994, Soliman [7] presented
two CCII-based circuits that equivalent to the Ker-
win-Huelsman-Newcomb biquad (KHN biquad) [8].
Both of these circuits use five CCIIs (three plus-type,
two minus-type), six (or seven) resistors and two
grounded capacitors to realize lowpass, bandpass and
highpass transfer functions simultaneously as in the
KHN circuit. In 1995, Senani and Singh [9] provided
another approach to realize KHN biquad using CCIIs.
The circuit uses five CCIIs (two plus-type, three mi-
nus-type), six grounded resistors and two grounded ca-
pacitors to obtain the lowpass, bandpass and highpass
filter functions. In 1996, Soliman [10] presented several
circuits that can realize lowpass, bandpass and highpass
filters simultaneously using CFAs. In 1997, Horng et al.
[11] proposed a lowpass, bandpass and highpass filter
uses four plus-type CCIIs and seven passive components.
Recently, several KHN biquads using various active
elements were proposed in [12-15]. However, the notch
filter cannot be obtained without additional circuitry fr-
om these circuit configurations [7-15]. In 1994, [16] Ch-
ang proposed a lowpass, bandpass and notch filter using
three CFAs, three resistors and two grounded capacitors.
In this paper, we proposed a voltage-mode biquadratic
filter with single input and three outputs using three
plus-type CCIIs, two grounded capacitors and five resis-
tors. Lowpass, bandpass and notch filters can be obtained
simultaneously from the same circuit configuration. With
respect to the previous CFA based lowpass, bandpass
and notch biquadratic filter circuit in [16], the proposed
circuit employs simpler active components (plus-type
CCIIs).
2. Circuit Description
Using standard notation, the port relations of an ideal
plus-type CCII can be characterized by
000
100
010
yy
x
x
z
z
iv
vi
iv

 

 


 

 

 
(1)

J. W. HORNG ET AL.
35
The proposed configuration is shown in Figure 1.
Assuming R3 = R4 = R5 = R, The transfer functions can be
expressed as
2
1
112 12
22
2
112 12
()
()
out
in
GG
VCC GGG
VGG
ss
CGG GCC




(2)
1
211 2
22
2
112 12
()
()
out
in
GG
s
VCGG G
VGG
ss
CGG GCC




(3)
2
211
3121212
22
2
112 12
()
()
out
in
GGG
s
VGGG CCGGG
VGG
ss
CGG GCC

 



(4)
From (2)-(4) it can be seen that a lowpass response is
obtained from Vout1, a bandpass response is obtained from
Vout2 and a notch response is obtained from Vout3. The
proposed circuit uses three plus-type CCIIs, two ground-
ed capacitors and five resistors. The design of using only
grounded capacitors is attractive, because grounded capa-
citor can be implemented on a smaller area than the float-
ing counterpart and it can absorb equivalent shunt capaci-
tive parasitics [17-19]. In all cases the resonance angular
frequency ωo and the quality factor Q are given by
12
1
oGCC
  (5)
and
121
2
GGG C
QGC

 (6)
The resonance angular frequency can be controlled by
G. The quality factor can be orthogonally controlled by
G1 or G2.
3. Sensitivity Analysis
Taking into account the non-idealities of the plus-type
V
in
V
out1
z
C
1
V
out3
CCII+
z
x y
CCII+
x
y
R
3
z
CCII+
x
y
C
2
R
1
R
2
R
4
R
5
V
out2
(3)
(2)
(1)
Figure 1. The proposed voltage-mode biquadratic filter.
CCII, the characteristics of the non-ideal CCII can be
given by iy = 0, iz = ()
s

ix and vx = ()
s

vy, where ()
s

and ()
s

represent the frequency transfers of the in-
ternal current and voltage followers of the plus-type
CCII, respectively. They can be approximated by the fo-
llowing first order lowpass functions [20].
() 1/
o
ss




 (7)
() 1/
o
ss




 (8)
where 0.9914,
o


9
3.8 10

  rad/s, 0.9999
o


,
9
6.48 10

  rad/s. Assuming the circuits are working
at frequencies much lower than the corner frequencies of
()
s

and ()
s

, namely, 1 () 1s

  and 1

(1

<<1) denotes the current tracking error and
2
() 1s



 and 2

(2

<<1) denotes the voltage
tracking error of the plus-type CCII. The denominator of
the non-ideal output voltage function for Figure 1 is
22
222 11
11233 12
() ()
GG
Dsss
CGG GCC



 
 (9)
The resonance angular frequency ωo and quality factor
Q are obtained by
11
12
oGCC



 (10)
and
1233 111
22 2
GGG C
QGC





 (11)
Because of the tolerances in component values and the
non-idealities of the plus-type CCIIs, the response of the
actual assembled filter will deviate from the ideal re-
sponse. As a means for predicting such deviations, the
filter designer employs the concept of sensitivity. The
sensitivity function is defined as:
y
x
yx
S
x
y

 (12)
The active and passive sensitivities of ωo and Q of the
proposed filter are:
1
o
ω
G
S

, 12 11
,
1
2
oo
ω
C,C
SS



, 12
12
+-
Q
G
GG
SGGG

,
1
1
12
+
Q
G
G
SGG G , 2
2
12
+
Q
G
G
SGG G

,
1211
,
1
2
QQQ
CC
SSS


 , 33
2
,
12
+
QG
SGG G


.

J. W. HORNG ET AL.
36
These values have been calculated by assuming that
1
α, 2 α, 3 α, 1
β
, 2
β
and 3
β
are near unity.
4. Simulation Results
The proposed circuit was simulated using PSPICE. The
plus-type CCII was implemented using one AD844. The
supply voltages are chosen as

12 V. The following set-
ting were selected to obtain the lowpass, bandpass and
notch filters: R1 = R2 = R3 = R4 = R5 = 1 kΩ, C1 = C2 = 1 nF
with Q = 1 and fo = 159.15 KHz. Figures 2 (a), (b) and
(c) represent the simulated frequency responses for the
lowpass (Vout1), bandpass (Vout2) and notch (Vout3) filters
of Figure 1, respectively. The simulation results are co-
herent with the theoretical analyses. The CCII has para-
sitic resistor from the z terminal to the ground (Rz [21]).
When the z terminal load of the CCII is a capacitor (C), it
in troduces a pole produced by Rz and C at low frequency.
This explains why Figure 2(b) has non-ideal phase res-
ponses at low frequencies. This effect can be minimized
by using larger loading capacitor or operating the filter in
high frequencies.
5. Conclusions
In this paper, a new single input and three outputs vol-
tage-mode biquadratic filter is presented. The proposed
circuit uses three plus-type CCIIs, two grounded capaci-
10
3
10
4
10
5
10
6
10
7
－ 80
－ 70
－ 60
－ 50
－ 40
－ 30
－ 20
－ 10
0
10
Frequency, Hz
Gain, dB
Theo. Simu.
o o o Gain
x x x Phase
-.-.-.-
Phase, deg
0
－ 180
－ 90
(a)
10
3
10
4
10
5
10
6
10
7
－ 50
－ 40
－ 30
－ 20
－ 10
0
10
Frequency, Hz
Gain, dB
Theo. Simu.
o o o Gain
x x x Phase -.-.-.-
Phase, deg
0
－ 180
180
(b)
10
3
10
4
10
5
10
6
10
7
－ 25
－ 20
－ 15
－ 10
－ 5
0
5
Frequency, Hz
Gain, dB
Theo. Simu.
o o o Gain
x x x Phase -.-.-.-
Phase, deg
0
－ 90
90
(c)
Figure 2. Simulated frequency responses of Figure 1 design
with C1 = C2 = 1 nF and R1 = R2 = R3 = R4 = R5 = 1 kΩ. (a)
lowpass filter (Vout1); (b) bandpass filter (Vout2), (c) notch
filter (Vout3).
tors and five resistors. The new circuit offers several
advantages, such as the realization of lowpass, bandpass,
and notch filter functions, simultaneously, in the same
circuit configuration; the use of only three plus-type CC
-IIs; orthogonally controllable of resonance angular fre-
quency and quality factor and the use of only grounded
capacitors.
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