Physical designing of low power operational amplifier
DEVENDRA SINGH KUSHWAHA
Department of Electronics and Communication
(Area of Specialization-VLSI Design)
Under the Guidance of
Topic- A Novel approach to Designing of
Low Power Operational Amplifier
Chapter 1 Introduction…………………………………………………………………………...3
Chapter 2 Literature survey and recent development……………………………………………
Chapter 3 Inferences drawn out of literature survey…………………………………………..15
Chapter 4 Problem formulation………………………………………………………………...17
Chapter 5 Scope of
Chapter 7 Expected Outcome…………………………………………………………………...24
Chapter 8 Tools and Software Requirement……………………………………………………
The operational amplifier is one of the most important and useful circuit in analog electronic
circuitry and Signal Processing. Designing and building an Operational Amplifier consist various
levels of complexities and hence make it a versatile device ranging from a dc bias generation to
high speed amplifications to filtering. One of the major applications of Operational Amplifiers
seems in Analog Signal Processing where wide varieties of circuits are made up, Operational
Amplifier as their integral part. Not only in Laboratories, Academia or institutions, it is very useful
components in industries as well. Operational Amplifier also plays a very important role in Digitals
Operational amplifiers had their origins in analog computers, where they were used to do
mathematical operations in many linear, non-linear and frequency-dependent circuits.
Characteristics of a circuit using an Operational Amplifier are set by external components with little
dependence on temperature changes or manufacturing variations in the Operational Amplifier itself,
which makes Operational Amplifiers popular building blocks for circuit design. The circuit symbol
for an Operational Amplifier is shown below,
Fig 1: Operational Amplifier structure
• V+: non-inverting input
• V−: inverting input
• Vout: output
• VS+: positive power supply
• VS−: negative power supply
The power supply pins (VS+ and VS−) can be labeled in different ways. Often these pins are left out
of the diagram for clarity, and the power configuration is described or assumed from the circuit.
The amplifier's differential inputs consist of a V+ input and a V− input, and ideally the Operational
Amplifier amplifies only the difference in voltage between the two, which is called the differential
input voltage. The output voltage of the Operational Amplifier is given by the equation:
Where V+ is the voltage at the non-inverting terminal, V− is the voltage at the inverting terminal and
AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback
loop from the output to the input).
Here in this project we are aiming to design and fabricate a novel low power Operational Amplifier.
To this approach we should first have known what the basic building blocks are for a better
Operational Amplifier. If we consider an ideal Operational Amplifier, an output can be received
using the characteristics like differential input, infinite voltage gain, infinite CMRR, infinite input
resistance and zero output resistance. Most of the ideal things are not ideally generated, but a proper
approach towards the idealness can make us achieve the properties that are close to them. In a real
Operational Amplifier however these characters cannot be generated but their performance has to
be sufficiently good for the circuit behavior to closely approximate the characters of an ideal
Operational Amplifier in most applications.
A basic Operational Amplifier consists of 4 main blocks namely
a. Current Mirror
b. Differential Amplifier
c. A Level shifter, differential to single ended gain stage
d. An Output buffer
Fig: 2 Circuit diagram of Operational Amplifier showing all stages
Fig: 3 An NMOS Current mirror
Fig:4 A Differential Amplifier
Fig: 5 Common Source stage with Current Source load
Fig 6: Block diagram of an Operational Amplifier
(a) Differential Voltage Gain: Infinite
(b) Common mode gain: Zero
(c) Input impedance (Zin): Infinite
(d) Output impedance, (Zout): Zero
(e) CMRR: Infinity
(f) Bandwidth, (BW): Infinite
(g) Offset Voltage, (Vo): Zero
LITERATURE SURVEY AND RECENT
W. T. Holman et al. (1) presented a low noise CMOS based Operational Amplifier in a 120nm
Digital Technology. The chip area is 3.0mm2
and a corner frequency less than 10Hz is found.
Gain Bandwidth Product 3.1MHz
Output Slew Rate 2.0V/us
Quiescent Current 0.75mA
Input Supply ±2.5V
As a part of wideband random noise generation.
This Operational Amplifier uses a standard differential input stage and a diode based
bootstrapped biased network.
The 1/f equivalent input noise can be reduced without affecting white noise by uniformly
scaling the width and length of the device after setting the value of the Trans conductance
to obtain the desired white noise level.
Ming-Dou Ker et al.  presented a CMOS Operational Amplifier in a 130nm low-voltage
process. In this
The effect of MOSFET gate-oxide reliability on Operational Amplifier is investigated
with the two stage and folded-cascode structures in a 130nm low voltage CMOS process
The test operation conditions include unity-gain buffer (closed loop) and comparator
(open loop) configuration.
The gate-oxide reliability in the Operational Amplifier can be improved by the stacked
configuration under small input and output application.
The following problems were faced of thin gate-oxide of the MOS transistor:
Hot carrier effect
All these problems effect the degrade the lifetime of the MOS transistor
The author used H-Spice for the simulation of the circuit and obtained 64.7dB and 47.8˚open-
loop gain and phase margin respectively.
Loikkanen. M et al. presented a high current CMOS Operational Amplifier. They told:
Low voltage CMOS Operational Amplifier, which is capable of driving heavy resistance
and capacitive loads.
Robust and power efficient compensation is achieved by using Miller Compensation
together with a high bandwidth stage.
Unity gain bandwidth (UGB) 5.7MHz
Phase margin 61˚
Current 2.4mA@ 1.5V power supply
At 3V supply the amplifier is able to source or sink more than 100mA into 1nF||10Ω load
The author uses compensation method
The Simple Miller Compensation (SNC) is a usable technique for driving heavy resistive
loads, due to its simplicity and robustness to withstand small signal trans conductance
variations of the output stage.
In this paper, theory and measurement results of a class AB power amplifier, which has
rail-to-rail input and output and uses miller compensation with the high bandwidth stage
to stabilize the amplifier.
A two pole, high speed Operational Amplifier modeling methods and techniques are presented
by Makris C.A et al. . They told that:
Settling time is very important parameter since it determines the maximum speed of the
operation of the circuit.
In this paper miller approximation is used to show a quite significant error when applied
to high frequency Operational Amplifier designs.
High frequency Operational Amplifier architectures are generally of two types
(a) Single stage externally compensated
(b) Two stage internally compensated
Schlogl, F. et al. described a 120nm Operational Amplifier with high gain down to ±0.3V
3-stage Operational Amplifier
120nm digital CMOS technology
86dB supply voltage range @ ±0.3V to ±0.6V
Positive feedback is primarily implemented for a good common-mode rejection
Transit frequency 46MHz
Phase margin 66˚ @±0.6V power supply
Current consumption less than 1.8mA in the temperature range -30˚C to +150˚C
Two pseudo cascodes in the input differential stage for gain enhancement
The fully differential circuits have many advantages compared to single ended circuits
This is so because if the signal voltage is doubled, the suppression of ground disturbances
is very good the input voltage range for Operational Amplifiers is about in the middle of
the power supply (no need of rail-to-rail input). Because of the higher signal voltage the
SNR can be increased.
A wide input voltage is achieved due to the bulk regulation of the input transistor
The pseudo cascodes have the advantage that they do not need biasing circuits compared
to normal cascodes
The positive feedback loads in the first and the second result in a good common mode
Kaulberg et al.  designs a CMOS current mode Operational Amplifier. It is known as a fully
differential input differential output current Operational Amplifier. Also it has
generation current conveyors
It can be configured to provide either a constant Gain-Bandwidth Product (GBP) in a
fully balanced current mode feedback amplifier or a constant bandwidth (BW) in a trans
impedance feedback amplifier.
The GBP is obtained as 3MHz
Offset current 0.8µA
Due to flexible interconnections of three 2nd
generation current conveyor, a versatile
current mode building block has been achieved.
Schlogl et al.  demonstrated a low voltage Operational Amplifier in 120nm digital CMOS
The power supply and the Early voltages are lowered as per the need (below about 10V
for gate lengths below 400nm) as well as the gain of the transistor stage is low.
In shrinking the threshold voltage of the transistors decreases less than supply voltage
The replica gain enhancement technique is affected due to mismatching of components
Another problem is that the multiple signal path causes a slow settling component in the
The fully differential circuits have many advantages compared to single-ended circuits.
The signal voltage is doubled, the ground disturbance suppression is very good and the
input voltage for Operational Amplifier is near the middle of the power supply(no need of
The gain was improved by about 20dB compared to simulations of a standard non-
cascoded two stage Operational Amplifier
A wide input range is achieved due to the bulk control of the input transistors
Schlogl et al.  designed a high-gain, high speed Operational Amplifier in digital 120nm
CMOS in fully differential 6-stage 3-signal path Operational Amplifier.
A differential gain of 120dB @1.2V power supply is obtained
The use of six common mode controller(CMC) leads to a good common mode behavior
and an AB output stage.
Unity gain frequency 866MHz
Phase margin 36˚
Slew rate 890V/µs
Stage 1: This input stage is a differential amplifier with P-channel transistor P1 and P2
and N-Channel load
Stage 2: This stage is realized with cascaded P-Channel input transistors and self-
cascaded N-Channel loads
Stage 3: In this third stage two signals paths are added
Stage 4: The amplifier stage 4 controls the N-channel output transistors
Stage 5: It controls the P-Channel output transistors
Stage 6: This last stage is used to correct the phase at high frequency and is
compensated by the load capacitances
Sarbishaei et al.  described a high gain, high speed low-power class AB Operational
A positive scheme is used to increase the voltage gain
Good utilization of current driven bulk technique the output voltage swing is improved
Two cross coupled flipped voltage follower blocks, class AB behavior is achieved to
make the Operational Amplifier compatible for high speed low power applications
Class AB technique was employed to get a higher slew rate with low power
To overcome the swing limitations, CDB technique was applied to load transistors to
decrease threshold voltage
This Operational Amplifier can be used as the first stage Operational Amplifier with rail-
Hiyuan Li ey al.  says that Low noise Operational Amplifier can be designed with current
driven bulk in 250nm CMOS technology. Also
Effect of substrate biasing on equivalent input referred voltage noise En, and presents a
low noise Operational Amplifier design with current driving bulk technology
250nm CMOS technology is used
It improves noise performance
@1MHz, GBP 280.5MHz, DC gain 76dB,
total Harmonic Distortion(THD) 76dB @50KHz
Power consumption 2.35mW @2.5V power supply
Current driven bulk is used as a technology for minimum noise
This Operational Amplifier has better noise performance, better linearity and Bandwidth
by smaller area and similar power dissipation
GBP is adequate for high frequency analog applications
Vincence et al. , in the study of Low Voltage Class AB Operational Amplifier tells that
Minimum selector circuit is used to control the Class AB operation of the output stage
The Operational Amplifier basic characteristics are analyzed and simulated using
SMASH 4.0 simulator with ACM model of the MOSFET
1.5V input, quiescent current 4.5µA for a unity gain frequency of 1MHz
Design integrated an AMS 0.8µm technology
Raikos et al.  says in the paper that
A low voltage Differential Amplifier is conducted by bulk-driven PMOS transistor
A local positive feedback is utilized that boosts the input trans conductance and improve
the noise performance
order Chebyshevs active RC filter with 500KHz cutoff frequency and 1dB ripple is
built based on the proposed amplifier
1V power supply voltage
350nm CMOS technology
Pletersek et al.  discusses Low supply voltage, Low noise fully differential programmable
gain amplifiers. He tells that
Low voltage, fully differential, low noise, programmable gain microphone amplifier is
Differential band gap reference and low voltage programmable gain power amplifier is
The measured equivalent input referred RMS noise voltage of 5.1nV/Hz1/2
in the voice
frequency band was achieved
The output buffer is capable of delivering 30mW power into 50Ω load at 3V power
J.Mahattanakul et al.  in their paper designed a two stage CMOS Operational Amplifier with
flexible noise power balancing scheme
2-stage CMOS Operational Amplifier design procedure
Balance between noise performance and power consumption
INFERENCES DRAWN OUT OF
The literature survey tells that
Most of the work has been done on 120nm CMOS technology
Noise can be reduced by adjusting the trans conductance of the CMOS device
Low noise Operational Amplifier can be designed with current driven bulk CMOS
The three main stages of Operational Amplifier are differential, level shifter and
Cascoded structures are better that cascades for enhanced gain. Hence designing
becomes better using Cascode connection
Miller Compensation Method
Class AB amplifier is used for better slew rate
Rail to rail Operation
Positive feedback is primarily implemented for a good common-mode rejection
The fully differential circuits have many advantages over single ended circuits
A wide input voltage range is achieved due to the bulk regulation of the input transistor
1. Finite Gain: Operational amplifiers are mainly used to amplify the input signal and the
higher its open loop gain the better as in many applications they are used with a feedback
loop, so ideal Operational Amplifiers are characterized by a gain of infinity. For practical
Operational Amplifiers, the voltage gain is finite. Typical values for low frequencies and
small signals are A = 102 – 105, corresponding to 40-100 dB gain.
2. Input impedance, (Zin): The Input impedance of an Operational Amplifier for an ideal
device has to be infinite to prevent any current flowing from the source supply into the
amplifiers input circuitry.
3. Bandwidth, (BW): An ideal operational amplifier has an infinite Frequency Response and
can thus be used to amplify signals of any frequency. However as evident from the
frequency response curve below the gain of the amplifier is not constant irrespective of
frequency and after the first pole it begins to drop with a slope of 20dB/decade thus the
higher the frequency of the first pole the higher the range of frequencies over which it
4. Finite Linear Range: The linear relation V0 = A (Va-Vb) between the input and output
voltages are valid only for a limited range of V0. Normally the maximum value of V0 for
linear operation is somewhat smaller than the positive dc supply voltage, the minimum
value of V0 is somewhat positive with respect to the negative voltage.
5. Offset Voltage: The amplifiers output is supposed to be completely independent of
common potentials applied to both inputs and is supposed to be zero when the voltage
difference between the inverting and non-inverting inputs is zero. For an ideal
Operational Amplifier, if Va = Vb (which is easily obtained by short circuiting the input
terminals) then V0 = 0. In real devices, this is not exactly true, and a voltage V0, off ≠ 0
will occur at the output for shorted inputs. Since v0,off is usually directly proportional to
the gain, the effect can be more conveniently described in terms of the input offset
voltage Vin, off, defined as the differential input voltage needed to restore v0=0 in the
real devices. For MOS Operational Amplifiers Vin, off is about 5-15mV.
6. Common Mode Rejection Ratio (CMRR): The common-mode input voltage is defined
by Vin,c = (Va + Vb)/2 as contrasted with the differential-mode input voltage Vin,d = Va
- Vb. The differential gain AD and also the common-mode gain AC which can be
measured as shown in figure, where Ac = V0/ Vin,c.
The CMRR is now defined as AD/Ac or in logarithmic value CMRR = 20 log10(AD /
Ac) in dB. Typical CMRR values for MOS amplifiers are in the 60-80 dB range. The
CMRR measures how much the Operational Amplifier can suppress common-mode
signals at its inputs. These normally represent undesirable noise, and hence a large
CMRR is an important requirement.
7. Frequency Response: Because of stray capacitances, finite carrier motilities and so-on,
the gain A decreases at high frequencies. It is usual to describe this effect in terms of the
unity gain bandwidth, that is the frequency f0 at which |A (f0)| = 1. For MOS Operational
Amplifiers, f0 is usually in the range of 1-10MHz. It can be measured with the
Operational Amplifier connected in a voltage-follower configuration.
8. Slew Rate: For a large input step voltage, some transistors in the Operational Amplifier
may be driven out of their saturation regions or completely cut-off. As a result the output
will follow the input at a slower finite rate. The maximum rate of change dV0/dt is called
slew rate. It is not directly related to the frequency response. For typical MOS
Operational Amplifiers slew-rates of 1~20 V/μs can be obtained.
9. Nonzero Output Resistance: For a real MOS Operational Amplifier, the open loop
output impedance is nonzero. It is usually resistive, and is of the order of 0.1-5KΩ for
Operational Amplifiers with an output buffer, it can be much higher (~1MΩ) for
Operational Amplifiers with un-buffered output. This affects the speed with which the
Operational Amplifier can charge a capacitor connected to its output and hence the
highest signal frequency.
10. Noise: The MOS transistor generates noise, which can be described in terms of an
equivalent current source in parallel with the channel of the device. The noisy transistors in
an Operational Amplifier give rise to a noise voltage von at the output of the Operational
Amplifier, this can be again modeled by an equivalent voltage source Vn = Von/A at the
Operational Amplifier input. Unfortunately, the magnitude of this noise is relatively high,
especially in the low frequency band where the flicker noise of the input devices is high; it
is about 10 times the noise occurring in an Operational Amplifier fabricated in bipolar
technology. In a wideband (say in the 10Hz to 1MHz range), the equivalent input noise
source is usually of the order of 10~50μV RMS, in contrast to the 3~5μv achievable for low-
noise bipolar Operational Amplifiers.
Fig:7 Despcription of 3rd
stage i.e. Level Shifter
SCOPE OF WORK
PARAMETERS SPECIFICATION OBJECTIVE(EXPECTED
SIMULATION AND LAYOUT)
Gain 10 V/V || 20 dB 10.3 V/V || 20.0 dB
3-dB bandwidth 20 kHz. 220KHz
Unity Gain Bandwidth(UGB) NA 3Mhz
CMRR >50 dB >80dB
PSRR NA 90dB/60dB
Slew Rate 10 v/μs 12 v/μs
Power Dissipation 1mW 0.45mW
Input Common Mode
Output Offset Voltage NA -500mV
The proposed work will be carried out following the sequential steps mentioned below:
Literature Survey and
Judge and justify the
Fig 8: Flowchart Showing the Methodology to Carry Out the Proposed Work
Scope of Work
Introduction to Software
Generating Netlist and placing components
Simulation and Waveform Analysis
Performance comparison between the results of modified swarm
-optimization and available methods
The following outcomes are expected by the investigator from the proposed work:
1. This new modified algorithm shall be able to find the best load management in different
2. The proposed system shall provide very effective and efficient residential load
3. The proposed algorithm shall make it possible to automatically adjust the consumption
of residential load in order to satisfy power constraints
4. Introduction of additional objective functions shall minimize the cost, since the rates of
electricity are different for peak hours and off peak hours.
Fig:9 BODE diagram of an Operational Amplifier showing pole, margin,gain @relevent
Fig:10 Frequency response of an ideal Operational Amplifier
TOOL AND SOFTWARE REQUIREMENT
The software tool needed for this proposed low-power Operational Amplifier is TANNER EDA
Tool version 13.0 or TANNER EDA Tool 15.1
Tanner IC Work Flow
Tanner Tools are fully-integrated solutions consisting of tools for schematic entry, circuit
simulation, waveform probing, full-custom layout editing, placement and routing, netlist
extraction, LVS and design rule checking (DRC) verification.
This document gives a rough overview of how to design & simulate things with Tanner Tools.
There are four basic steps:
1. Design the schematic in S-EDIT.
2. Simulate the schematic to make sure it behaves as you expect using T-SPICE.
3. Layout the schematic in L-EDIT.
4. Perform an LVS (Layout VS Schematic) to make sure your layout is functionally the
same as the schematic you designed in S-EDIT.
5. Simulate the layout using T-SPICE with a high-level spice model, making sure L-EDIT
generates the parasitic capacitances so they are included in the simulation.
 W. T. Holman, J. A. Connelly, J. O. Perez, “A Low Noise Operational Amplifier in a 1.2μM
Digital Technology”, IEEE Journal 2007
 Maryam Borhani, Farhad Razaghian, “Low Power Operational Amplifier Based on Weak
Inversion with Miller-Cascoded Frequency Compensation”, IEEE Journal 2009.
 Ming-Dou Ker; Jung-Sheng Chen, “Impact of MOSFET Gate-Oxide Reliability on CMOS
Operational Amplifier in a 130-nm Low-Voltage Process”, IEEE Journal 2008.
 Loikkanen. M, Kostamovaara. J, “High current CMOS operational amplifier”, IEEE
 Makris C.A, Toumazou. C, “Two pole, high speed operational amplifier modelling, mehods
and techniques”, IEEE Conference 1989.
 Schlogl, F.; Dietrich, H.; Zimmermann, H. “120nm CMOS operational amplifier with high
gain down to ±0.3V supply”, IEEE Conference 2003, Pages: 121 – 124.
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 Schlogl, F.; Zimmermann, H. “Low-voltage operational amplifier in 0.12 μm digital CMOS
technology” IET Journal 2004, Pages: 395 – 398.
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digital 120nm CMOS”, IEEE Conference 2004, Pages: 316 – 319.
 Sarbishaei, H.; Kahookar Toosi, T.; Zhian Tabasy, E.; Lotfi, R. “A high-gain high- speed
low-power class AB operational amplifier”, IEEE Conference 2005, Pages: 271- 274 Vol. 1
 hiyuan Li; Jianguo Ma; Mingyan Yu; Yizheng Ye “Low noise operational amplifier design
with current driving bulk in 0.25μm CMOS technology”, IEEE Conference 2005 , Pages: 630 -
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amplifier”, IEEE Conference 2001, Page(s): 207 – 211.
 Rajput, S.S.; Jamuar, S.S., “Low voltage, low power, high performance current mirror for
portable analogue and mixed mode applications”, IET Journal 2001, Page(s): 273 – 278.
 Rajput, S.S.; Jamuar, S.S., “Ultra low voltage current mirror op amp and its applications”,
IEEE Conference 2002, Page(s): 145 - 148 vol.1.
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Page(s): 136 – 139.
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programmable gain amplifiers”, IEEE Conference 1995 , Page(s): 105 – 112.
 J.Mahattanakul and J.Chutichatuporn, “Design Procedure for Two-Stage Cmos Operational
Amplifier Flexible noise power balancing scheme” IEEE trans.Circuits syst.I fundam.Theory
App vol 52 no.8 pp 1508-1514 Aug 2005.
 J.Mahattanakul ,“Design Procedure for Two-Stage Cmos Opamp employing current buffer”
IEEE trans. Circuits syst.II Fundam. Theory App vol. 52 no.8 pp 1508-1514 Nov 2005.
 Behzad Razavi, Design of CMOS Analog Integrated Ckts, Mc-Graw Hill College, 2001.
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portable analogue and mixed mode applications." In Proc. IEE Circuits Devices and Systems,
2001, vol. 148, no. 5 pp. 273-278.
 C. Zhang, A. Srivastava, P. K. Ajmera, "A 0.8 V CMOS amplifier design", Analog
Integrated Circuits and Signal Processing, 47, pp 315-321, 2006, Springer Science.
 Analog MOS Integrated Circuits for Signal Processing by Roubik Greogorian Gabor C.
 P.E. Allen and D.R. Holberg, CMOS Analog Circuit Design, Oxford University Press: New
 http://webpages.ursinus.edu/lriley/ref/circuits/node5.html for opamp amplifier circuits
 http://talkingelectronics.com/projects/OPERATIONAL AMPLIFIER/OPERATIONAL
AMPLIFIER-1.html for calculating gain
 http://wn.com/differential_amplifier Video Lecture