CONVERTING THREE-STAGE PSEUDO-CLASS AB AMPLIFIERS TO TRUE CLASS AB ...

101 Pages·2011·2.67 MB·English

CONVERTING THREE-STAGE PSEUDO-CLASS AB AMPLIFIERS TO
TRUE CLASS AB AMPLIFIERS
BY
PUNITH REDDY SURKANTI, B.Tech
A dissertation submitted to the Graduate School
in partial fulfillment of the requirements
for the degree
Master of Sciences, Engineering
Specialization in: Electrical Engineering
New Mexico State University
Las Cruces, New Mexico
March 2011
“CONVERTINGTHREE-STAGEPSEUDO-CLASSABAMPLIFIERSTOTRUE
CLASSABAMPLIFIERS,”adissertationpreparedbyPUNITHREDDYSURKANTIin
partial fulfillment of the requirements for the degree, Master of Sciences has been
approved and accepted by the following:
Linda Lacey
Dean of the Graduate School
Chair of the Examining Committee
Date
Committee in charge:
Dr. Paul M. Furth, Associate Professor, Chair.
Dr. Jaime Ramirez-Angulo, Professor.
Dr. Jeffery Beasley, Professor.
ii
DEDICATION
DedicatedtomymotherLalitha, fatherMadhava Reddy, sisterDr. Avanthi
Reddy, my advisor Dr. Paul Furth and all my friends and family members.
iii
ACKNOWLEDGMENTS
I would like to thank my parents Lalitha Surkanti and Madhava Reddy
Surkanti for their support and their confidence. And my sister Dr. Avanthi
Reddy Surkanti, who encouraged me to complete my Master’s in USA. She is a
role model for me, who inspired me for what I have done.
A teacher is treated as a god next to our patents. I thank Dr. Paul M.
Furth for advising me throughout my Master’s degree. I learned much from his
teaching through courses like digital VLSI and Image Sensors; learned how to
do research and research philosophy through his research. I assisted Dr. Furth
in preparing lectures for a course titled EE590: Integrated Power Management.
During that time, I learned the teaching skills, how to prepare lectures, how to
think and how to explain so that the students can understand. All of this has
helped me in explaining concepts to the students. I thank his family with whom
we spent time on Thanksgiving day every year. We play sports and fun games
and had some good food on that day. I will never forget those memories.
Great appreciation and thanks to Dr. Jaime Ramirez-Angulo for accepting
myrequesttobeamemberofmythesiscommittee. ItooktwomajorVLSIcourses
under him which helped me in learning good concepts in analog design. He is a
good and energetic professor and helped a lot during our labs. I wish that I can
work with him in collaborated research to know his research type and philosophy.
iv
Beyond his busy schedule as a head of the department for Engineering
Technology, I thank Dr. Jeffery Beasley for accepting my request to be a member
of my thesis committee.
Thanks to my cousins, Vineela, Nithin, Prathyusha, Panchi, Pranaya,
Pravalika, Sanvitha, Maninder and all my relatives.
I would like to thank my undergraduate friends, Nevil Kranthi, Dhanun-
jay Reddy, Ram Reddy, Bharath Reddy, Rajiv Reddy, Nikhil Reddy, Raj kumar,
Rajesh, Naresh Reddy, Manoj, Shashank, Kamesh, Shyam, Vinod.
I would like to thank my seniors in las cruces, Pulla Reddy, Koushik, An-
najirao, Wasequer, Praneeth. They helped me learning concepts in VLSI and
choosing my research.
Thanks to my friends in las cruces, Chaitanya Mohan, Harish Valapala,
Rajesh, Ramesh, Venkat Reddy, Nikhilesh, Suresh, Karunakar, Arun, Sandeep,
Santhosh SK, Varun, Sravan, Lalith, Venugopal, Madhusudhan Reddy, Srini-
vasu Pudi, Vamshidhar Reddy, Srikanth Reddy, Sriharsh, Harish Nammi, Nitya,
Chayya, Sailaja. I would like to thank all the members of Indian Student Associ-
ation (ISA) for supporting me.
Thanks to Adam Crittenden for correcting grammar, tense and spellings
in my thesis report.
v
VITA
April 16, 1987 Born in Nizamabad, India.
Education
2004 - 2008 B.Tech. Electronics and Computer Engineering,
JNTU, India
2008 - 2011 MSEE. in Electrical Engineering,
New Mexico State University, USA - GPA 3.6/4.0
Presentations
[1] Converting Three-Stage Pseudo-Class AB Amplifier to a True Class AB Am-
plifier, Graduate Research and Art Symposium (GRAS), New Mexico State Uni-
versity, March, 2011.
Experience
Teaching Assistant, Electrical Engineering, NMSU, Fall-2009, Spring 2010, Fall
2010, Spring 2011
1. Assist students in the labs and in the projects for EE161: Problem Solving in
C.
2. Prepared lecture material with the advise of Dr.Paul Furth for EE590: Inte-
grated Power Management which deals with LDO’s, band-gap reference, DC/DC
converters, regulator design, charge pump and battery charging circuits
3. Taught some lectures and assist students in the lab for EE590: Integrated
Power Management.
vi
ABSTRACT
CONVERTING THREE-STAGE PSEUDO-CLASS AB AMPLIFIERS TO
TRUE CLASS AB AMPLIFIERS
BY
PUNITH REDDY SURKANTI, B.Tech
Master of Sciences, Engineering
Specialization in Electrical Engineering
New Mexico State University
Las Cruces, New Mexico, 2011
Dr. Paul M. Furth, Chair
A widely-adopted low voltage, low transistor count, high gain and wide
swing three-stage pseudo-class AB amplifier is converted to a true class AB ampli-
fier. The conversion is made possible by using gate-drain feedback to combine two
inverting common-source amplifiers to form a single non-inverting amplifier. The
circuit is stable for a wide range of capacitive and resistive loads. The class AB
amplifier has a dc gain of 81.7dB and unity gain frequency of 6.58MHz when
driving a load of 100pF||10kΩ. Maximum output currents are 1.12mA of sourcing
and 1.14mA sinking current from the positive and negative power rail respectively
with a quiescent current of 95µA, when operating from ±1.25V power supply and
drivinga1kΩload. ThisdemonstratestheclassABcharacteristicoftheamplifier.
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Both pseudo-class AB and true class AB amplifiers were fabricated in a 0.5µm
CMOS 2P3M technology and measured to characterize their differences.
A novel inverting current buffer compensation technique for multi-stage
amplifiers is proposed. The compensation capacitor from the output is connected
to the bias node that helps in increasing the bandwidth and improving the power
supply rejection ratio. This also helps in increasing the driving capability for a
wide range of load capacitor values.
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TABLE OF CONTENTS
LIST OF TABLES xii
LIST OF FIGURES xiii
1 INTRODUCTION 1
2 LITERATURE REVIEW 4
2.1 Multi-Stage Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Compensation Techniques . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Miller Compensation . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Ahuja Compensation . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 Nested Miller Compensation . . . . . . . . . . . . . . . . . 8
2.2.4 Reverse-Nested Miller Compensation . . . . . . . . . . . . 9
2.2.5 Miller Compensation with Inverted Current-Buffer . . . . . 10
2.3 Class AB Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 I-I-N Pseudo Class-AB Amplifier [1] . . . . . . . . . . . . . 11
2.3.2 Pseudo-Class AB to True Class AB Amplifier using Adap-
tive Biasing proposed in [2] . . . . . . . . . . . . . . . . . 13
3 DESIGN AND SIMULATIONS 15
3.1 I-I-N Three-stage Pseudo-Class AB Amplifier . . . . . . . . . . . 15
3.1.1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
ix
3.1.2 Small-Signal Analysis . . . . . . . . . . . . . . . . . . . . . 17
3.2 I-N-I Three-stage Pseudo-Class AB Amplifier . . . . . . . . . . . 20
3.2.1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.2 Small-Signal Analysis . . . . . . . . . . . . . . . . . . . . . 23
3.3 Inverted Current-Buffer Compensation . . . . . . . . . . . . . . . 25
3.3.1 Inverted Current Buffer . . . . . . . . . . . . . . . . . . . 25
3.3.2 Small-Signal Model . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Simulation Results Compared with Inverted Current-Buffer Com-
pensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.4.1 AC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.4.2 Transient Analysis . . . . . . . . . . . . . . . . . . . . . . 32
3.4.3 Power-Supply Rejection Ratio . . . . . . . . . . . . . . . . 34
3.5 I-N-I Three-stage Class AB Amplifier . . . . . . . . . . . . . . . . 37
3.5.1 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.5.2 Nested Inverted Current-Buffer Compensation . . . . . . . 39
3.5.3 Small-Signal Analysis . . . . . . . . . . . . . . . . . . . . . 40
3.6 Proposed Three-stage True Class AB Amplifier . . . . . . . . . . 43
3.6.1 Gate-Drain Feedback . . . . . . . . . . . . . . . . . . . . . 44
3.6.2 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.6.3 Nullified Effect of Inverted Current-Buffer Compensation . 46
3.6.4 Small-Signal Analysis . . . . . . . . . . . . . . . . . . . . . 47
3.7 Simulation Results Compared with the Proposed Class AB Amplifier 48
3.7.1 DC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.7.2 AC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.7.3 Transient Analysis . . . . . . . . . . . . . . . . . . . . . . 54
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