View
5
Download
0
Category
Preview:
Citation preview
E E 435 Assignment 2
Amplifiers
Jasmin Ivankovic
1. 28. 20
]\
ProblemsI have included the problems here for quick reference, making this report a self-
contained piece for my research notes.
1
]\
2
]\
3
]\
About / GoalsFor this assignment, I will be researching and drawing conclusions about
operational amplifiers. The following are the tasks and what they aim to teach
me:
● Reading research articles which will give me insights as to how Op Amps
are developing
● Analytically expressing/manipulating Op Amp equations to gain insights
into their underlying characteristics
● Identifying key features between voltage and current Op Amps
● Working out the details of many textbook representations of Op Amps
● Drawing conclusions about why positive feedback is less common in
textbooks when looking at Op Amps
Research Questions The questions here guide my research and help with completing the assignment
in such a way which maximizes learning. These sets of questions are represented
with different headers. The solutions can be found in the following section,
“Research Notes,” and mostly consist of pictures or notes taken from online
sources, including a link as citation. In response, I shall try to examine the cited
material under scrutiny in the same section.
● Initial Questions
○ How do I set up small signal equations for the amplifier in problem 1?
4
]\
○ What is a transresistance amplifier?
■ What are the equations for it?
○ What is a common mode feedback circuit?
● Questions After Problem Set
○ What exactly is compensation, and how does it apply to Op Amps?
Solutions / NotesThe answers to the above questions are here.
➢ Research Questions
➢ Setting up small signal equations
○ the following was taken from Dr. Geigers’s lecture 7 slides from the
previous semester
■ this sets an example for making node voltage equations for a
cascode amplifier
5
]\
➢ Definition of transresistance amplifier
6
]\
7
]\
After reading the above paragraph on allaboutcircuits.com, I understand the
result found in problem 3. You want a high output resistance because the output
is voltage, and you do not want a huge drop on the device you are connecting
the output to. Similarly, you want the input resistance to be small so that the
current flows without degradation.
➢ Understanding CMFB
○ The following was taken from Dr. Geiger’s Lecture 20 Spring of 2012
8
]\
9
]\
10
]\
11
]\
12
]\
13
]\
14
]\
15
]\
16
]\
17
]\
18
]\
➢ Problem 1 & 2
➢ The following is my attempt at deriving the ss equations for the above
listed amplifier.
○ first I transformed the schematic to a small signal model
○ I derived equations using node voltage
19
]\
V x : gm1 ¿
V y :gm3 (V y )+gm1 ¿
V out : gm4 (V y )+gm2¿
gm1 ¿
I worked on this on a white board for a while, here’s a summary of how far I
got. It would take significantly more effort to solve this. This reminds of
solving Laplace’s equations in E & M.
➢ Problem 3
➢ Part A I’m deriving the voltage gain equation in terms of trans-resistance
V out=−RT [V outR2
+V ¿
R1]
20
]\
−V ¿
RTR1
=−V out [1+RTR2
]
A=V out
V ¿=
−RTR1
1+RTR2
⮚ Part B What happens if the trans-resistance approaches infinity?
A=−R2R1
➢ Problem 4
➢ Part A I’m deriving an analytical equation for W/L to have the desired
output
IDQ=W2 LμCox¿
WL
= 4mA12μC ox¿¿
21
]\
➢ Problem 5 & 6
➢ Design a 5T op amp without the need for a CMFB circuit
➢ http://tnt.etf.bg.ac.rs/~ms1aik/AIC-15_OTA_FD
➢
Conclusions
What was learned
Ultimately, by trying for analytical solutions I found that these calculations
have a high level of complexity and am grateful for the ways that have been
22
]\
developed to simplify our lives. There’s much more research for me to be done.
And I am excited by the prospects that this course offers longform.
23
Recommended