Download Design and Simulation of Operational Transconductance Amplifier

International Journal of Electronics, Electrical and Computational System
IJEECS
ISSN 2348-117X
Volume 4, Special Issue
March 2015
Design and Simulation of Operational Transconductance
Amplifier Using CMOS CCII
*Rashmi Pandey,** Dr. Jasdeep Kaur Dhanoa,*** Dilpreet Badwal
*Dept. of Electronics and Communication Engineering,
IGDTUW, Kashmere Gate, Delhi-110006, India
**Associate Professor, Dept. of Electronics and Communication Engineering,
IGDTUW, Kashmere Gate, Delhi-110006, India
*** Assistant Professor , Department of Electronics Engineering, JSSATE NOIDA.
Abstract- In this work, a high bandwidth
CMOS OTA is designed and simulated using
PSPICE software. Two CMOS based singleended second generation current conveyor are
used in order to design Operational
Transconductance Amplifier. The circuit is
realised by connecting a resistor between two
CCII. The circuit consist of CMOS CCII with
less number of transistors, thus fulfilling the
requirement of small size. The proposed
circuit is operating in subthreshold region at
±0.1V dc power supply and gives the good
characteristics for ac, dc and transient analysis.
The proposed approach is boosting the
bandwidth and reducing the power dissipation
of the designed circuit to a far extent. The
designed OTA consumes only 0.283nW power
at ±0.1V of power supply. The circuit has a
bandwidth of 1.162 GHz at 3dB gain and
gives high o/p impedence in the range of 500650MΩ in wide frequency range, thus the
values are very attractive. The circuit is
simulated using 0.18um technology and the
simulation results are presented herewith.
KEYWORDS- Second Generation Current
Conveyor(CCII), Operational Transconductance Amplifier(OTA), VCCS.
I. INTRODUCTION
The demand for low power and low voltage
devices due to increase in the digital
348
integration and analog circuits within a single
chip, has become a challenge in the research
for analog designers. This trend of smaller size
has forced most basic analog building blocks
to be redesigned, so as to guarantee their
performance same or even better than their
operation for larger power supplies. Also, the
increasing components on a chip demands
lower power consumption and thus the
reasonable method to reduce power
consumption is by minimizing the supply
voltage. The need for low voltage, low power
circuits are immense in portable electronics
equipments like laptops, pacemakers, cell
phones etc. And is also a crucial important
requirement for power efficient circuits. Low
voltage circuits with higher bandwidth can be
more easily realised using current-mode
circuits as compared to voltage-mode
approach[1]. Current mode circuits have the
advantage of wider bandwidths, large
linearity, higher slew rate and wider dynamic
range than their voltage mode counterparts,
thus they receive considerable attention[2].
Current Conveyors are based on a current
mode approach and are used in applications
ranging
from
analogue
computation,
oscillators, universal and multifunction filters
etc. Current Conveyor has simple architecture,
wider bandwidth and can operate at low
voltage[3]. There are three generations of
Rashmi Pandey, Dr. Jasdeep Kaur Dhanoa, Dilpreet Badwal
International Journal of Electronics, Electrical and Computational System
IJEECS
ISSN 2348-117X
Volume 4, Special Issue
March 2015
Current conveyors CCI, CCII, CCIII. CCII is
the most widely used Current Conveyor
among the three generations due to its
versatile configurations. CCII have low
impedence at X-terminal and high impedence
at output terminal Z. When operated in subthreshold region, CCII can be used for ultra
low voltage and ultra low power applications.
Operational Transconductance Amplifier is
voltage controlled current source. It replaces
Operational Amplifier because of its high
bandwidth, high voltage swing, high SNR
even at low voltages and also due to its unique
characteristics suited for applications such as
gain control, multiplexing, comparator, analog
modulation, active-C filters, amplifiers,
oscillators, mixers switching circuits and
many more. Thus OTA constitute as a major
building block in analog designing[5]. Thus a
high bandwidth OTA operating at low voltage
is designed in this paper.
In this paper, a fully differential OTA is
designed using two CMOS based CCII and a
resistor. The circuit is simulated using PSPICE
180nm technology. In the proposed work a
resistor is connected between the X terminals
of both CCII[4]. The circuit is operated in
subthreshold region at ±0.1V of dc supply.
Also, the input voltage is given at the terminal
Y of both the CCII and the output current is at
terminal Z. Output current is obtained through
Z terminal of both the current conveyors.
Since the circuit gives current as output in
response to voltage at input terminal so the
circuit operates as OTA VCCS.
II. OPERATIONAL TRANSCONDUCTANCE AMPLIFIER
The OTA is a current-mode circuit and a
versatile amplifier that converts input voltage
to linearly proportional output differential
current with transconductance gain „Gm‟.
They provide more reliable performance at
higher frequencies because of the current
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mode operation and even they require just a
few or even no resistors for their internal
circuitry. The principle applications of OTA
include electronically controlled applications
such as variable gain amplifier stages, filters,
variable frequency oscillators. These circuits
are quite difficult to be implemented using
opamps.
In an ideal OTA, output current doesnot
depends on ouput voltage. The differential
voltage between input terminals controls the
current through output node. The relation
between the differential input voltage and the
output current depends linearly on the
transconductance gain Gm. OTAs provide
highly linear electronic tunability of their
transconductance(Gm). The transfer function
of the OTA gives relation between input
voltage and output current.
Iout = (Vin+ - Vin-). Gm
(1)
Iout = Gm Vin
(2)
where Gm is transconductance gain, Iout is
output current and Vin is input voltage. OTAs
provide highly linear electronic tunability of
their transconductance (Gm).
Vout = Iout . Ro
(3)
The relation shows that the output current is
not dependent upon the voltage at the output
node. The symbol and equivalent circuit of
OTA is shown.
Fig. 1 OTA symbol and equivalent circuit
For various applications OTA must have
characteristics[6] such as:
 Higher transconductance gain
 High bandwidth(≥1GHz)
 Low power dissipation
Rashmi Pandey, Dr. Jasdeep Kaur Dhanoa, Dilpreet Badwal
International Journal of Electronics, Electrical and Computational System
IJEECS
ISSN 2348-117X
Volume 4, Special Issue
March 2015
 High output impedance
 Slew rate(≥0.5V/ns)
III. CCII BASED OTA
The CCII is an active circuit[7] with three
ports X, Y, Z. Port X is a low impedence
input/output port, port Y is a high impedence
input port and port Z is a high impedence
output port. CCII is most useful of the current
conveyor family types with wide range of
applications. It is very suitable building block
for design of the active-RC filters or number
of special admittance converters and also for
low voltage applications CCII is starting to be
very powerful building block. In the last
decade the numbers of high speed and wide
range opamps are based on current conveyor
structure.
The matrix of second generation current
conveyor has been formulated as follows
(4)
Iy = 0 ; Vx = Vy, ; Iy = ± Ix
(5)
A CCII can be used to realize a single ended
OTA[4]. In this paper, OTA is designed using
two CCII and a resistor connected between the
X port of both the CCII, i.e. CCII1 and CCII2.
The proposed circuit has less number of
transistors and simpler geometry. The MOS
used to implement the circuit have small
aspect ratio. The circuit symbol of OTA using
CCII is shown in fig.2
Fig. 2
Circuit symbol of CCII based OTA
In the ckt shown in fig. 3 by Mai M.
Kamel[4], OTA is designed using CCII,
operating at 1V dc voltage. Also circuit has 19
transistors. In the proposed circuit all the
transistors are made to operate in subthreshold
region which is the best region of power
saving. Also, the circuit has only 16 transistors
which minimize the parasitics and increases
the power consumption efficiency of the
designed circuitry. Proposed circuit is shown
in fig. 4
Fig. 3 OTA circuit designed by Mai M. Kamel[4]
350
Rashmi Pandey, Dr. Jasdeep Kaur Dhanoa, Dilpreet Badwal
International Journal of Electronics, Electrical and Computational System
IJEECS
ISSN 2348-117X
Volume 4, Special Issue
March 2015
Fig. 4 Circuit Diagram of Proposed CCII based OTA
In proposed circuit, Fig 4, transistors M1, M2,
M3, M4, M5, M6, M7, M8 forms CCII1
where X port is at gate of M1 and Y port is at
gate of M2. CCII2 is formed by transistors
M9, M10, M11, M12, M13, M14, M15, M16
such that gate of M9 is port X and gate of M10
is port Y.
IV. SIMULATION RESULTS
Operational Transconductance Amplifier
proposed in this paper, as shown in fig.4, is
designed in 180nm technology from TSMC.
The OTA has been simulated at VDD of ±0.1V.
All the transistors have same channel length of
Fig. 5 Frequency response of CCII based
0.18µm. Aspect ratios of different transistors
OTA
in proposed OTA is shown in table. 1
40
20
0
-20
100Hz
1.0KHz
10KHz
DB((V(7)-V(12))/(V(13)-V(14)))
100KHz
1.0MHz
10MHz
100MHz
1.0GHz
10GHz
100GHz
Frequency
650M
600M
550M
500M
100Hz
1.0KHz
(V(7)-V(12)) / ID(M7)
10KHz
100KHz
1.0MHz
10MHz
100MHz
1.0GHz
Frequency
TABLE 1. Aspect ratio for various
transistors
Fig. 5 shows simulated frequency response of
designed OTA for R=1KΩ. The gain of
proposed OTA is positive 20.42dB and -3dB
frequency is obtained at 1.162GHz. The
simulation static power dissipation is only
2.83e-10 W.
351
Fig. 6 Output Impedence of OTA at port Z
For good operation of OTA it must have high
impedence at output node. Fig. 6 shows the
output impedence curve at various frequencies
at the output node Z. The simulated result
shows that impedence at node Z is 500MΩ at
lower frequency and increases upto 650MΩ at
even higher frequencies. Fig. 7 shows the
range of voltage at node X that follows voltage
Rashmi Pandey, Dr. Jasdeep Kaur Dhanoa, Dilpreet Badwal
International Journal of Electronics, Electrical and Computational System
IJEECS
ISSN 2348-117X
Volume 4, Special Issue
March 2015
at node Y. The simulation result shows that
the voltage at node X, Vx closely follows Vy,
voltage at node Y, in the range of bias voltage.
Sinusoidal response of Vx and Vy is done
through transient analysis at respective nodes
and is shown in fig. 8.
transistors and gives good results at higher
frequencies.
200mV
Table 2 OTA simulation result of proposed
circuit and previous work
100mV
0V
-100mV
-200mV
-200mV
V(3)
-150mV
-100mV
-50mV
-0mV
50mV
100mV
150mV
200mV
V(8)
Vy
Fig. 7 Variation of voltage at port X wrt
voltage at port Y
100mV
0V
-100mV
0s
5ms
V(3)
10ms
15ms
20ms
25ms
30ms
35ms
V(8)
Time
Fig. 8 Sinusoidal response of voltage at port
X and Y
-60
-70
-80
-90
1.0Hz
10Hz
DB(ID(M16)/V(3))
100Hz
1.0KHz
10KHz
100KHz
1.0MHz
10MHz
100MHz
1.0GHz
Frequency
Fig. 9 Transconductance gain Gm versus
frequency
The transconductance gain of OTA is given by
(6)
Fig. 9 gives the curve of Transient Gain Gm
wrt frequency.
Various parameters of proposed circuit are
compared with that of previous work. Table 2
compares both of the OTA.
V. CONCLUSION
OTA is realized based on CMOS CCII using
180nm technology. The designed OTA has
high output impedence, high bandwidth and
minimal power dissipation of 0.283nW. Also
the designed OTA has less number of
352
VI. REFERENCES
[1]. “A Review of Current Mode Active
Blocks” by Indu Prabha Singh, Meeti Dehran
and Dr. Kalyan Singh, Dr. S. N. Shukla
[2]. “Analog IC Design: The Current-Mode
Approach” C.Toumazou, F.J. Lidgey, and D.
Haigh, Exeter, UK: Peter Peregrinus,1990.
[3]. “Design and Analysis of CMOS Current
Conveyor” Amruta Bhatt, Journal of
information, knowledge and research in
electronics and communication engineering
issn: 0975 – 6779| nov 12 to oct 13 | volume –
02, issue - 02 page 785
[4]. “High Bandwidth Second Generation
Current
Conveyor
based
Operational
Transconductance Amplifier” Mai M. Kamel,
Eman A. Soliman 2011 IEEE
[5]. “DESIGN AND SIMULATION OF
CMOS OTA WITH 1.0V,55db GAIN & 5Pf
load” IJMPICT Vol.5 No.2 June 2014
[6]. “A High CMRR, High Slew Rate, Low
Total Harmonic Distortion CMOS OTA for
HF Applications” Anup Mane, Deepa Yagain.
Second International Conference on Emerging
Trends in Engineering and Technology,
ICETET-09
[7]. A. Sedra and K. Smith, "A secondgeneration
currnt
conveyor
and
its
applications," IEEE Tras. Circuit Theory vol.
CT-I7, no. I, pp.132-134, February 1970.
Rashmi Pandey, Dr. Jasdeep Kaur Dhanoa, Dilpreet Badwal