Circuits and Systems, 2011, 2, 65-73
doi:10.4236/cs.2011.22011 Published Online April 2011 (http://www.SciRP.org/journal/cs)
Copyright © 2011 SciRes. CS
Electronically-Controlled Current-Mode Second Order
Sinusoidal Oscillators Using MO-OTAs and Grounded
Capacitors
Data Ram Bhaskar1, Kasim Karam Abdalla1, Raj Senani2
1Department of Electronics and Communication Engineering, Faculty of Engineering and Technology,
Jamia Millia Islmia, New Delhi, India
2Division of Electronics and Communication Engineering, Netaji Subhas Institute of Technology, Delhi, India
E-mail: senani@nsit.ac.in
Received December 17, 2010; revised February 9, 2011; accepted February 21, 2011
Abstract
Five new electronically-controllable second order current-mode sinusoidal oscillators using three multi-
output operational transconductance amplifiers (MO-OTAs) and two grounded capacitors (GC) have been
presented. Simulation results are included to confirm the theoretical analysis based upon CMOS OTAs im-
plementable in 0.5 µm technology.
Keywords: Oscillators, Analog Electronics, Current Mode Circuits, Operational Transconductance
Amplifiers
1. Introduction
Recently, Tsukutani, Sumi and Fukui [1] presented two
current-mode OTA-C sinusoidal oscillators each of which
employs three MO-OTAs and three grounded capacitors
(GC) and provides three explicit current outputs. How-
ever, whereas one of the circuits of [1] does not have in-
dependent controllability of the condition of oscillation
(CO) and the frequency of oscillation (FO) through dif-
ferent transconductances (which is not only a desirable
but also an expected property which one likes to see in
any OTA-C oscillator), on the other hand, both the cir-
cuits employ three GCs and hence, are not canonic.
The main objective of this paper is to present five new
current-mode electronically-controllable second order
sinusoidal oscillators which use only three MO-OTAs
like the circuits of [1] but in contrast to the circuits of [1],
the proposed circuits use no more than two GCs and are
capable of providing a non-interacting and independent
control of both CO and FO and in addition also provide
quadrature outputs which find numerous applications
(for instance, in communications for quadrature mixers
and single-sideband generators and in instrumentation
for vector generator or selective voltmeters [2] etc.).
2. The Proposed Circuits
The proposed circuits are shown in Figure 1. For an
ideal MO-OTA with transconductance gm, the current
output Io is given by Io = gm (V+V), where V+ and V
are the input voltages at non-inverting input terminal and
inverting input terminal respectively. Routine analysis
yields, the condition of oscillation (CO) and the fre-
quency of oscillation (FO) for all circuits as summarized
in Table 1, which also shows the relevant modes of
availability of quadrature outputs in all cases. From the
expressions of FO given in Table 1, it can be easily de-
duced that magnitude of all active and passive sensitivi-
ties of FO, in all the five circuits, would be in the range
of 0 to 1/2 and circuits thus, enjoy low sensitivity prop-
erties.
3. Simulation Results
To verify the validity of the proposed configurations,
circuit simulation of the oscillators has been carried out
using the CMOS MO-OTA circuit from [1] (presented
here as Figure 2). In PSPICE simulation, implementa-
tion was based upon a CMOS OTA in 0.5 µm technol-
ogy. The aspect ratios of the MOSFETs were taken as
shown in Table 2. The CMOS OTAs were biased with
DC power supply voltages VDD = +2.5 V, VSS = 2.5 V.
The generated waveforms, transient and the frequency
spectrum for the proposed circuits obtained from simula-
tions are shown in Figure 3, Figure 4 and Figure 5,
D. R. BHASKAR ET AL.
Copyright © 2011 SciRes. CS
66
1
C
m3
+
-
+
+
m1
+
g
-
+
+
m2
+
g
-
+
+
g
2
C
+
I02
I03
I01
(1)
1
C
m3
+
g
-
+
+
2
C
m2
+
g
-
+
+
m1
+
g
-+
++
I02
I03
I01
(2)
1
C
m3
+
g
-
+
+2
C
m2
+
g
-+
+
m1
+
g
-+
+
+I02
I03
I01
(3)
1
C
m3
+
g
-
+
+2
C
m1
+
g
-
+
+
m2
+
g
-
+
+I03
I02
I01
(4)
1
Cm1
+
g
-
+
+
2
C
m3
+
g
-
+
+
m2
+
g
-
+
+
+I02 I01
I03
(5)
Figure 1. Proposed configurations.
respectively. The element values used in the simulations
along with the theoretical and practical output frequency
and total harmonic distortions (THD) for the proposed
circuits are summarized in Table 3. All the proposed
oscillators have been checked for robustness using
Monte-Carlo simulations, however, to conserve space, a
sample result has been shown in Figure 6 for the oscil-
lator (5) of Figure 1, which confirms that for 15% vari-
ations in the value of gm3, the value of oscillation fre-
quency remains close to its normal value of 1.1996 MHz
and hence almost unaffected by change in gm3 (which
should be the case since gm3 does not feature in the ex-
pression of FO).
In all cases, a very good correspondence between de-
signed values and those observed from PSPICE simula-
tions has been obtained. The simulation results, thus,
confirm the workability of the proposed configurations.
4. Comparison with Other Previously
Known OTA-Based Oscillators
It is now useful to compare the proposed new circuits
with some of the earlier proposed OTA-based oscillators.
Recently, Kamat, Anand Mohan and Prabhu [3] presented
a quadrature oscillator employing two MO-OTAs, two
single output OTAs and two GCs. The circuit does not
have independent controllability of CO and FO. It may
also be recalled in this context that much earlier, in refer-
ence [4], two minimum-component electronically-tunable
sinusoidal oscillators using two OTAs and two GCs had
been presented however, these circuits too did not have
independent controllability of CO and FO. Furthermore,
there is another class of OTA-based RC oscillators known
earlier [5-9] which employ one or two OTAs along with a
number of resistors and two capacitors. However, when
these OTA-RC oscillators from [5-9] can be transformed
into OTA-C oscillators, by simulating the resistors with
OTAs, the resulting entirely-OTA-based oscillators will
g
m2
g
m3
I
o2
I
o3
I
o1
g
m1
C2
C1
g
m1
gm3
gm2
I
o3
I
o2
I
o1
C2
C1
gm3
g
m2
g
m1
C1
C2
I
o1
I
o2
I
o3
I
o2
I
o3
I
o1
g
m1
g
m2
g
m3
C1
C1
I
o2
gm3
gm1
gm2
I
o1
I
o3
C1
C2
D. R. BHASKAR ET AL.
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67
VSS
M1M2
3M4
M7M8
5M6
M9
M11
M
2
M1
M10
M
VDD
Ibias
+Io
-IoVin
+
Vin
-
Figure 2. MO-OTA.
Table 1. Condition of oscillation and frequency of oscillation for the proposed circuits.
Table 2. Aspect ratios of MOSFETs used in the MO-OTA
implementation.
MOSFET W(µm) L(µm)
M1, M2 20 1.8
M3, M4, M5, M6, M9,
M10
43 0.5
M7, M8, M11, M12 43 1.25
not remain as efficient and practically viable due to the
requirement of an excessive number of OTAs.
In comparison, the new circuits are free from above
mentioned deficiencies of the circuits presented earlier in
[3-9].
5. Concluding Remarks
Five new current-mode electronically controllable
OTA-C sinusoidal oscillators have been presented. Like
the recently proposed circuits of [1], the proposed circuits
also employ only three MO-OTAs and grounded capaci-
tors as preferred for IC fabrication [10] and [11]. How-
ever, by contrast to the circuits presented in [1] both of
which require three capacitors and hence are non-canonic,
the proposed circuits require only two capacitors and
hence, are canonic. All the proposed circuits enjoy the
feature of independent controllability of oscillation fre-
quency and condition of oscillation, which is not avail-
able in one of the circuits presented in [1]. The new cir-
cuits are also free from the drawbacks of the circuits pre-
sented earlier in [3-9]. Also, all the proposed circuits pro-
vide quadrature outputs as an additional feature not
available in the circuits of [1]. The active and passivesen-
sitivities of all the circuits are very low. The workability
Circuit
No.
Condition of
Oscillation (CO)
Frequency of
Oscillation (FO)
Availability of
Quadrature Outputs
1 (gm3gm1) 0 12
12
1
2
mm
gg
CC

22
12
om
o
Is
g
I
ssC
,

212
332
omm
om
Is
g
g
I
sgsC
2 (gm2gm1) 0 23
12
1
2
mm
g
CC

33
11
om
o
Is
g
I
ssC
,

33
21
om
o
Is
g
I
ssC
for gm1 = gm2
3 (gm1gm2) 0 23
12
1
2
mm
g
CC

33
11
om
o
Is
g
I
ssC
,

33
21
om
o
Is
g
I
ssC
for gm1 = gm2
4 (C2 gm3C1 gm1) 0 12
12
1
2
mm
gg
CC

11
21
om
o
Is
g
I
ssC
5 (gm2gm3) 0 12
12
1
2
mm
gg
CC

121
331
omm
om
Is
g
g
I
sgsC
,

11
21
om
o
Is
g
I
ssC
Ibias
VSS
+Io
VDD
Io
in
V in
V
D. R. BHASKAR ET AL.
Copyright © 2011 SciRes. CS
68
(a)
(b)
(c)
(d)
D. R. BHASKAR ET AL.
Copyright © 2011 SciRes. CS
69
(e)
Figure 3. Output waveforms of (a) circuit 1 (b) circuit 2 (c) circuit 3 (d) circuit 4 (e) circuit 5.
(a)
(b)
(c)
D. R. BHASKAR ET AL.
Copyright © 2011 SciRes. CS
70
(d)
(e)
Figure 4. Output transient of (a) circuit 1 (b) circuit 2 (c) circuit 3 (d) circuit 4 (e) circuit 5.
(a)
(b)
D. R. BHASKAR ET AL.
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71
(c)
(d)
(e)
Figure 5. Frequency sp ectru m of (a) circuit 1 (b) circuit 2 (c) circu it 3 (d ) circuit 4 (e) circuit 5.
of the proposed circuits has been demonstrated by SPICE
simulation results.
The transconductance of an OTA is temperature de-
pendent this calls for appropriate temperature compensa-
tion for which numbers of schemes are known in the
literature [12-14]. However, the study of modified ver-
sions of the proposed circuits incorporating temperature
compensation would require considerable additional
work; therefore, it was considered to be outside the scope
of present work. Lastly, it may be mentioned that the
D. R. BHASKAR ET AL.
Copyright © 2011 SciRes. CS
72
Figure 6. Result of the Monte-Carlo Simulation of oscillator circuit (5) of Figure 1.
Table 3. The values of the capacitors and transconductances for various oscillators.
Circuit
No.
gm1
(mA/V)
Ib1
(mA)
gm2
(mA/V)
Ib2
(mA)
gm3
(mA/V)
Ib3
(mA)
C1
(nF)
C2
(nF)
FTheoretical
(MHz)
FPractical
(MHz) THD
1 0.7954 2.8 0.7954 2.8 0.712 1.47 0.1 0.1 1.265918 1.277 2.6%
2 0.793 2.73 0.715 1.5 0.804 3.4 0.120.1 1.101566 1.1803 5.2%
3 0.7523 1.95 0.794 2.75 0.7718 2.26 0.070.071.732487 1.734 1.6%
4 0.7954 2.8 0.7046 1.4 0.788 2.6 0.110.111.083157 1.1514 2.3%
5 0.785 2.53 0.715 1.5 0.777 2.36 0.1 0.1 1.192361 1.1996 1%
circuits proposed in this paper are inspired by the ideas
contained in [15-19].
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