Download III. operational transconductance apmlifire (ota) design

ISSN: 2278 – 7798
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 2, Issue 1, January 2013
A description of OTA the topologies of OTA and
discussion of telescopic type of OTA
Sourabh Singh Chouhan, Devendra Singh Ajnar, Pramod Kumar Jain

Abstract— This paper gives a description about of OTA
(Operational Transconductance Amplifier).It gives design
concept of telescopic type of OTA and a brief description about
different topologies of OTA. The .18µm CMOS process is used
for design and simulation of this OTA. This OTA uses a biasing
current of 15.6µA with vdd and vss of 1.25 V and -1.25V
successively. The designand simulation of this OTA is done
using CADENCE spectre enviroment with UMC 0.18 µm
technology file. The simulation results of this OTA shows that
the open loop gain of about 78.16dB. this OTA is having CMRR
230dB.
Index Terms —OTA,Topologies of different OTA, Cadence,
CMRR , CMOS IC Design.
I. INTRODUCTION
Due to recent development in VLSI technology, the size of
transistors decreases and power supply also decreases. The
OTA is a basic building block in most of analog circuits with
linear input output characterstics. The OTA is widely used in
analog circuits such as neural networks, Instrumentation
amplifire, ADC and filter circuits. The Operational
transonductance amplifire has similarity with Operational
amplifire (OPAMP) in which both have differantial inputs.
The basic difference between OTA and OPAMP is, OPAMP
is voltage controlled voltage source (VCVS) and OTA is
voltage controlled current source (VCCS) i.e. the OPAMP
output is in form of voltage since OTA is transconductance
amplifire so it converts voltage into current.
Figure 1.
The bottom transistor Qb is used as a current source; unnder
normal circumstance, its drain voltage V is large enough that
the drain current Ib is devided between Q1 and Q2 is a
sensitive function of the difference between V1 and V2.
B. Simple transconductance amplifire
The schematic for the transconductance amplifire is shown
in figure 2. The circuit of a differential pair and single current
mirror, like the one shown in figure 2. Which is used to
subtract the drain current is thus equal to I1-I2
II. BASIC OF OTA
A. Differential pair
Input signals represented as a difference between
two voltages. These circuits all use some variant of
the differential pair shown in Figure as an input stage.
Because the differential pair is so universal useful.
Sourabh Singh Chouhan, Dept of Electronics & Instrumentaton,
S.G.S.I.T.S,., (e-mail: [email protected]). Indore, India,
09407407167,
Devendra Singh Chouhan, Dept of Electronics & Instrumentation,
S.G.S.I.T.S,Indore, India,
Pramod Jain , Dept of Electronics & Instrumentation,
S.G.S.I.T.S,Indore, India,
Figure 2
C. Wide range amplifires
A simple transconductance amplifire will not generate
output voltage below Vmin, which , in turn , is dependent on
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All Rights Reserved © 2013 IJSETR
ISSN: 2278 – 7798
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 2, Issue 1, January 2013
the input voltages. This limitation often is a source of
problems at the system level, because it is not always
possible to restrict the range of input coltages. We can
remove this restriction however , by addition to the circuit,
as shown in figure 3
voltage is VDD=1.25 and VSS=-1.25V. The input AC a signal is
7.49mV, 10GHz. the OTA is characterized by various
parameters like Gain at dc (AV),Unity gain bandwidth,Input
common mode range (Vin(min) and Vin(max)), Load capacitor
(CL). The design parameter of this OTA is shown in below in
below table II.
There are several different OTA’s are used in which this
OTA is a simple OTA is a simple OTA with and high gain.
The OPAMP is characterized by various parameters like open
loop gain, Bandwidth, Noise etc. the performance Measrures
are fixed Due to Design parameters such as Transistor size,
Bias current and etc. In this paper we describe design of OTA
amplifier and design is done in 0.19µm technology.
Figure 3
D.
Various topologies of ota
There are four topologies of OTA.
(1) Single stage OTA.
(2) Two stage OTA.
(3) Gain boosted OTA.
(4) Folded cascode OTA.
E. Comparision between different topologies
The table presents a comparioson of basic OPAMP
paramerters for different configuration described above
described topologies in table 1
Figure 4
Operation Transconductance Amplifier
TABLE II
TRANSISTOR SIZE
Topology
Two stage
Telescopic
Cascode
Gain
boosted
Folded
cascode
TABLE I
Gain
Outputswing
High
Highest
Medium Medium
Speed
Power
Low
Highest
Medium
Low
High
Medium
Medium
Highest
Medium
Medium
High
Medium
III. OPERATIONAL TRANSCONDUCTANCE APMLIFIRE (OTA)
DESIGN
Figure 4 shows the schematic of Operational
Transconductance Amplifier (OTA). In this OTA the supply
DEVICE
PMOS Transistor
NMOS Transistor
W/L(µm)
10/01
05/01
IV. SIMULATION RESULTS
The design of this Operational transconductance Amplifier
(OTA) is done using Cadence Tool. The simulation results are
done using Cadence Spectre Enviroment using of the OTA
shows that the open loop gain of approximately 78.16dB. The
OTA has GBW of about 30.40MHz.
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All Rights Reserved © 2013 IJSETR
ISSN: 2278 – 7798
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 2, Issue 1, January 2013
The Table III shows the simulated result of the OTA. The AC
response which shows gain and phase change with frequency
is shown in figure 5. Figure 6 shows schematic for CMRR
anakysis.
TABLE III
Specification
Values
CMOS technology
0.18µm
Open Loop Gain
78.16dB
Supply voltage
+1.25v
Load capacitance
1.0pF
CMRR
230dB
Gain Margin
35.06Db
Phase Margin
90.25o
Unity Gain BW
30.46MHz
Figure 6
Schematic for CMRR analysis
V. SIMULATED CHARACTERSTICS OF OTA
Figure 7
Common mode and differential mode gain
Figure 5
AC response showing gain and phase change
with frequency
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All Rights Reserved © 2013 IJSETR
ISSN: 2278 – 7798
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 2, Issue 1, January 2013
[5]
Y. Tsividis, Operation and Modeling of the MOS Transistor, 2nd ed.
Boston, MA: McGraw-Hill, 1998.
[6]
D. A. Johns and K. Martin, Analog Integrated Circuit Design. New
York: Wiley, 1997.
[7]
Phillip E. Allen and Douglas R. Holberg “CMOS analog circuit
design” ,second edition, Oxford university press, 2007,pp. 269-274.
Sourabh Singh Chouhan
He has currently persuing M.Tech with specialization in Microelectronics
and VLSI Design at S.G.S.I.T.S, Indore, India. He received his Bachelor
degree in Electronics and Instrumentation Engineering from Institute of
Engineering and Technology, Indore.
D. S. Ajnar
Figure 8
Calculation of Unity Gain BW
VI. CONCLUSION
In this paper we present a simple Telescopic
Cascoded Operational Transconductance Amplifier (OTA)
topology for low voltage and low power applications. This
OTA can be used in low power, low voltage and high time
constant applications such process controller, physical
transducers and small battery operated devices. This work can
be in biquad filter design, ADC design and instrumentation
amplifiers because of its high gain, high CMRR and low
power consuption.
REFERENCES
[1]
J. H. Botma, R.F. Wassenaar, R. J. Wiegerink, “A low voltage CMOS
Op Amp with a rail-to-rail constant-gm input stage and a class AB
rail-to-rail output stage”, IEEE 1993 ISCAS, Chicago, pp.1314-1317..
[2]
Paul R. Gray, Paul L.Hurst, Stephan H.Lewis and Robort G.Mayer
“Analysis and design of analog integrated circuits”,Forth Edition, John
Wiley & sons, inc.2001, pp.425-439.
[3]
Adel S. Sedra, Kenneth C.Smith “Microelectronic Circuits”, Oxford
university press, Fourth edition ,2002,pp.89-91.
[4]
Jin Tao Li, Sio Hang Pun, Peng Un Mak and Mang I Vai “Analysis of
Op-Amp
Power-Supply
Current
Sensing
Current-Mode
Instrumentation Amplifier for Biosignal Acquisition System”,IEEE
conference,August-2008,pp.2295-2298.
He has received the B.E. degree in Electronics and Communication
Engineering from D.A.V.V University, India in 1993 and M.E. Degree in
Digital Techniques & Instrumentation Engineering from Rajiv Gandhi
Technical University Bhopal, India in 2000. He has been teaching and in
research profession since 1995. He is now working as Associate Professor in
Department of, Electronics & Instrumentation Engineering S.G.S.I.T.S,
Indore, India. His interest of research is in Designing of analog filter and
Current-Conveyor.
P.K. Jain
He has received the B.E. degree in Electronics and communication
Engineering from D.A.V.V. University, India in 1987 and M.E. Degree in
Digital Techniques & Instrumentation Engineering from Rajiv Gandhi
Technical University Bhopal, India in 1993. He has been teaching and in
research profession since 1988. He is now working as Associate Professor in
Department of Electronics & Instrumentation Engineering, S.G.S.I.T.S.
Indore, India. His interested field of research is analog circuit design.
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