Circuits and Systems, 2010, 1, 54-58
doi:10.4236/cs.2010.12009 Published Online October 2010 (http://www.SciRP.org/journal/cs)
SIMO Transadmittance Mode Active-C Universal Filter
Neeta Pandey1, Sajal K. Paul2*
1Department of Electronics and Communications, Delhi Technological University, Delhi, India
2Department of Electronics and Instrumentation, Indian School of Mines, Dhanbad, India
Received August 6, 2010; revised September 10, 2010; accepted September 13, 2010
Abstract
This paper presents two transadmittance mode universal filters having single voltage input and multiple cur-
rent outputs. The filter employs three multiple output current controlled conveyors (MOCCCII) and two
grounded capacitors. It can realize low pass, high pass, band pass, notch and all pass responses. As desired,
the input voltage signal is inserted at high impedance input terminal and the output currents are obtained at
high impedance output terminals and hence eases cascadability. The filter enjoys low sensitivity performance
and low component spread; and exhibits electronic and orthogonal tunability of filter parameters via bias
currents of MOCCCII. SPICE simulation results confirm the workability of the proposed structure.
Keywords: Universal Filter, Transadmittance Mode, Current Controlled Conveyor
1. Introduction
There has been substantial emphasis on development of
current conveyor based filters in the recent past which
can be attributed to its high performance properties such
as wider signal bandwidths, greater linearity, larger dy-
namic range, lower power consumption, simple circuitry
and occupy lesser chip area than their voltage mode
counterparts [1]. The filters employing operational trans-
conductance amplifier (OTA) possess lower dynamic
range with power supply scaling as its input are voltage
dependent. The need for lower power consumption re-
quires low bias current and hence lower output current
[2]. The OTA requires bias current of four times the cur-
rent needed by current controlled conveyor (CCCII) [3]
for the same transconductance. Thus circuits based on
CCCII consume lesser power than OTA based circuits.
The maximum usable frequency range depends strongly
on bias current, hence high frequency response of CCCII
based implementations are expected to be better than
OTA. Already a number of voltage and current mode
filter structures based on current conveyor have been
reported in the literature [3-13] and references cited
therein. A voltage-mode (VM) circuit is one whose signal
states are computed as node voltages while a current-
mode (CM) circuit is one whose signal states defined by
its branch currents. In some applications there is need of
filtering a voltage signal and then converting it to current
signal by using a voltage to current converter (V→I)
interfacing circuit. The total effectiveness of the elec-
tronic circuitry can be increased if signal processing can
be combined with V→I interfacing. A transadmittance
mode filter is suitable for such applications and finds
usage in receiver base band blocks of modern radio sys-
tem [14]. A careful study indicates that a limited literature
is available on transadmittance mode filter [14-18]. These
circuits can nicely perform the operation of transadmit-
tance mode filter, but still there is scope to improve them
in the following fronts: use of floating passive compo-
nents [14-18] which is not considered good for IC im-
plementation point of view; input voltages are not applied
at high impedance terminal [14,16,18]; availability of
output currents through passive components [17] thus
there is requirement of additional hardware; and filter
parameters are not electronically tunable [17]. It thus
reveals that no literature is available on transadmittance
mode universal filter that can simultaneously possess the
following advantageous features: 1) use of all grounded
passive components, 2) high impedance terminal for input
excitation, 3) output at high impedance and 4) electronic
tunability of filter parameters.
In this work, two current controlled conveyor based
transadmittance mode universal filter circuits are pro-
posed based on [10-13] that use only three MOCCCIIs
and two grounded capacitors. The first structure provides
band pass, high pass and notch responses simultaneously
and all pass and low pass responses can be obtained by
connecting together appropriate outputs. The low pass,

N. PANDEY ET AL. 55
band pass, high pass and notch responses are simultane-
ously available in the second proposed structure and all
pass response can be obtained by connecting together
suitable outputs. As desired, in both the structures, the
input voltage signal is inserted at high impedance input
terminal and the output currents are obtained at high im-
pedance output terminals. The filter parameters are ad-
justable through bias currents of MOCCCII. The filter,
under all operations, exhibits low active and passive sen-
sitivities. The function of the proposed structure has been
confirmed by SPICE simulations.
2. Circuit Description
The port relationships of a MOCCCII as shown in Fig-
ure 1 can be characterized by
0
|()|,
XYXX
vviRI 0,
Y
i
Z
X
ii

where the positive and negative signs denote the positive
and negative current transfers. Rx is the input resistance
at x port which can be controlled via bias current I0 [3].
The MOCCCII can be realized using bipolar transistor or
CMOS (Figure 2), the value of Rx is given as
0
2/ IVR TX  for bipolar realization or MOS transistors
operating in weak inversion region, where VT is the
thermal voltage; whereas 24 1/( )
Xmm
Rgg

 for MOS
transistors operating in strong inversion [19], where
0
2(/)
mii oxii
g
CWLI  .
The first proposed transadmittance mode universal filter
is shown in Figure 3, which employs three MOCCCIIs
and two grounded capacitors. The routine analysis of the
circuit yields the following transfer functions:
1
1
1
()
out
in x
I
VRDs
 ,222
1()
out x
in x
I
sC R
VRDs
,
2
3122
()
out x
in
I
sCCR
VDs
 ,
2
41212
1
1
()
outx x
in x
IsCCRR
VRDs

 (1)
where 2
12 1 222
() 1
xx x
DssCCRRsCR (2)
Thus the proposed structure of Figure 3 can be viewed
Figure 1. Circuit symbol of MOCCCII.
Figure 2. CMOS representation of MOCCCII [19].
Figure 3. First proposed structure.
as single-input four-output transadmittance mode uni-
versal filter. It provides low pass, band pass, high pass
and notch responses at Iout1, Iout2, Iout3 and Iout4 respec-
tively. The all pass responses can easily be obtained by
adding Iout1, Iout2 and Iout3. Furthermore, the input voltage
is applied at high impedance y-port and all the current
outputs are available at high impedance z-port of current
controlled conveyors that enable easy cascadability with-
out the need of supplementary buffer circuit.
All the filters are characterized by
1/2
0
1212
1
xx
RRCC




, 0
011
1
x
QRC

 and
1/2
11
0
22
x
x
RC
QRC



(3)
It may be noted from (3) that 0

can be adjusted by
varying bias current I02 (or2
x
R) without disturbing
00
/Q

and similarly 0

and 0
Q are orthogonally ad-
justable with simultaneous adjustment of I01 and I02.
The second proposed structure is shown in Figure 4,
which uses two MOCCCIIs and a minus type CCCII and
two grounded capacitors. The transfer functions for the
circuit of Figure 4 can be expressed as
2
1122
()
out x
in
I
sCCR
VDs
, 21
()
out
in
I
s
C
VDs
, 311
1
()
()
out x
in x
I
Ds sCR
VRDs


(4)

N. PANDEY ET AL. 56
Figure 4. Second proposed structure.
where
2
12 1 222
() 1
xx x
DssCCRRsCR (5)
Thus the second structure can also be viewed as sin-
gle-input three-output transadmittance mode universal
filter. It provides high pass and band pass responses at
Iout1 and Iout2. The notch response is available at Iout3 for
equal capacitors C1 = C2 and bias currents I01 = I02. The
low pass and all pass responses can easily be obtained by
adding Iout1 and Iout3; and Iout2 and Iout3 respectively. Like
the previous one, both the input and output impedances
are high for input voltage and output currents respec-
tively.
The results of active and passive sensitivity analysis of
various parameters for both the proposed filters are given
as
00 00
1212xx
RRCC
SSSS
 
 −1/2,
0000
1212xx
QQQQ
RRCC
SSSS 1/2
Hence the sensitivities of pole ω0 and quality factor Q0
are low and within unity in magnitude. Thus the propos-
ed structure can be classified as insensitive.
The Equation (3) also indicates that high values of
Q-factor will be obtained from moderate values of ratios
of passive components i.e., from low component spread
[20]. These ratios can be chosen as 12 (/ )
xx
RR

12 0
(/ )CC Q

. Hence the spread of the component val-
ues becomes of the order of0 Q. This feature of the
filter related to the component spread allows the realiza-
tion of high 0 Q values more accurately compares to the
topologies where the spread of passive components be-
comes 0 Q or 2
0
Q.
3. Comparison
Table 1 shows the comparison of the present work with
the previously reported works [14-18]. The study of Ta-
ble 1 reveals the following.
1) [14] uses the same number of active components as
that of present work, whereas the number of passive
components are more in [14] and most of them are float-
ing. Input impedance is low which is not desirable for a
circuit having input as voltage signal. The NF and AP
responses are not obtainable from this circuit.
2) [15] uses more number of active and passive com-
ponents than that of the present work and most of the
passive components are floating. Input impedance is low
and NF and AP responses are not possible as that of [14].
3) Although [16] and [17] use single active component,
the number of passive components are more and some of
them are floating. [16] has low input impedance and can
implement only AP response. [17] can implement only
LP and BP responses which are available through pas-
sive components, hence requires some more active com-
ponents (opamps, CC etc.) to use these responses.
Table 1. Comparison of the present work with the previously reported works.
Ref. No. and type of active
components
No. and type
of passive
components
No. of inputs and
input impedance
Possible output responses and
output impedance
Simultaneous
outputs
[14] 3 CCII
2 floating R
1 grounded R
2 floating C
Single, low input
impedance
LP, BP, HP all at high output
impedance;
NF and AP not possible
3
[15] 3 PFTFN realized
using 6 CFOA
2 floating R
1 grounded R
2 floating C
Single, low input
impedance
LP, BP, HP all at high output
impedance;
NF and APF not possible
3
[16] single CCIII
2 floating R
1 grounded R
1 grounded C
Single, low input
impedance
Only AP response at high output
impedance 1
[17] Single opamp
1 floating R
1 grounded R
1 grounded C
Single, high input
impedance
LP and BP output Current through
passive components; HP, AP, NF
not possible
2
[18] 2CDTA
2 floating R
1 floating C
1 grounded C
Three, low input
impedance
LP, HP, BP, AP, NF all at high
output impedance 1
Present
work 3CCCII 2 grounded C
Single, high input
impedance
LP, HP, BP, AP, NF all at high
output impedance 4 & 3

N. PANDEY ET AL. 57
4) [18] is a good proposition which uses only two ac-
tive components and implements all responses of uni-
versal filter. However, it suffers form the drawback of
using excessive numbers of passive components and
most of them are floating and also input impedance is
low which is not desirable for a transadmittace mode
filter.
Hence it reveals that the present work removes most of
the drawback which were prevailing in transadmittance
mode universal filter reported till date.
4. Simulation Results
To validate the theoretical predictions, the proposed filter
is simulated with SPICE using schematic of MOCCCII
as given in Figure 2 [19] using AMS 0.35 m CMOS
technology with dimensions of the NMOS and PMOS
transistors as that of [19] and supply voltages of 1.5
volts. Figure 5 shows the simulation results for circuit of
Figure 3 with the component values of C1 = C2 = 10 pF
and I01 = I02 = 100 µA. The total power dissipation of the
proposed filter is found to be approximately 10 mW.
The simulations have also been carried out to show the
dependence of f0 on bias current and results are shown in
Figure 6 for band pass response. It is found that f0 de-
pends linearly for low bias currents whereas for higher
bias current the dependence is approximately propor-
tional to the square root of the bias current. The percent-
age total harmonic distortion (%THD) variation with the
sinusoidal input signal is also studied and the results are
shown in Figure 7. It shows that the %THD is low and
remains within the acceptable limit of 5% [21] till the
considerable high input signal of 800 mV.
5. Conclusions
Two new single-input mutiple-output transadmittance
Figure 5. Simulated results for low pass, band pass, high
pass and notch responses.
Figure 6. Dependence of central frequency on bias current.
Figure 7. Variation of THD with input signal amplitude.
mode universal filters using three MOCCCII and two
grounded capacitors have been presented. The simulation
results verify the theory. It is found from the comparison
that the present work removes most of the drawback of
the previously reported works [14-18]. The salient fea-
tures of the proposed circuits are as follows: use of only
three MOCCCIIs and two capacitors, uses grounded pas-
sive components, low sensitivity performance, orthogo-
nal and electronic tunability of 
0 and Q0, high input and
output impedances which ease cascadability and low
component spread for high Q application.
6. References
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N. PANDEY ET AL. 58
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