IEEE Solid-States Circuits Magazine - Spring 2022 - 77

T
SSCS Circuit Analysis and Design Contest:
The objective of the IEEE Solid-State
Circuits Society (SSCS) International
Student Circuit Contest is to engage
students in thought-provoking circuit
analysis and design problems.
Submissions are solicited from both
undergraduate and graduate students
currently enrolled in a college
or university.
Some News
From this year, the circuit contest
will change to a more flexible and
engaging format. Starting from a list
of components, students will need
to design and simulate a circuit by
using the greatest number of components
with the goal of finding an
elegant circuit
topology. Some additional
rules and conditions apply.
Getting curious? Scan the QR code on
this page and try yourself!
Please also spend some time promoting
the contest among students
you know. A fantastic award is waiting
for the contest champion.
Question for the SSCS Contest 2020
Provide an example of an amplifier
where, despite the presence of a positive
feedback, the system cannot latch
since the topology guarantees an always-positive
gain margin (regardless
of the component values or mismatches).
In your answer, please clarify the
The Winners of the 2020-2021 Edition and Some News
expression of the loop gain and show
that there is actually a positive feedback
but that the magnitude can never
exceed one.
The Two Winners and Their Solutions
Mahdi Yektaei
School: Shahed University,
Tehran, Iran.
Mahdi Yektaei received
his B.Sc. degree
from Shamsipour
Digital Object Identifier 10.1109/MSSC.2022.3162133
Date of current version: 25 June 2022
Technical College, Tehran, Iran, in
2015 and, as an M.Sc. student, joined
the Integrated Circuits and Systems
Laboratory, Shahed University, Tehran,
in 2016. He has been a teaching
assistant with the Digital Electronics
Laboratory at Shahed University
since 2017. From 2013-2015, he was
with the start-up company RayeneAndis-Arsin,
and, in 2015, he was an
electronics designer for the start-up
company Rabo, both in Tehran. From
2018 to 2019, he was with Pars-Hesgar-Damun,
Tehran, developing a circuit
of measurement for farming.
His research interests include MOS
current mode logic, energy-efficient ICs,
serial links (SerDes), and low-voltage
and ultralow-power circuits in the wireline
and wireless applications. In 2012,
he scored in the top 1% (417/46,095)
for the entrance exam for the undergraduate
degree and received the Best
Inventor Award from the National Sahand
Research and Technology Festival;
he also received the Best Idea
Award from Shahed University in
2019. He has two patents and published
one paper in IEEE Transactions
on Very Large-Scale Integration Systems.
He was a reviewer for 23 manuscripts
for IEEE Transactions of Circuits and
Systems I, IEEE Transactions of Circuits
and Systems II, the IEEE 2021 International
Symposium on Circuits and
Systems, the 2021 IEEE International
Midwest Symposium on Circuits and
Systems, and IEEE Access.
Student Circuit Contest Solution
According to the three points in this
regard, the following are true:
■ There is a positive feedback.
■ The system cannot latch.
■ The topology always guarantees a
positive gain margin.
Indeed, latching contains the amplification
and positive feedback;
then, if we do not need a latch, but
the feedback is positive, we could
reduce the amplifier gain.
Introduction
A simple latch circuit is illustrated
in Figure 1(a) [1]. Also, the feedback
is positive, and the closed-loop gain
is
AV /AA1 b=-^h, as presented in
Figure 1(b) [2]. The feedback factor
is FA1 b=- whenever F 11 . In
addition, the stability is important
for the positive gain margin, and
we would like to not have the poles
and zeros at the right of the imaginary
axis for the closed loop. Consequently,
if
01F ,11 the function
will be stable, and, as a matter of
fact, in Figure 1(c), the transfer functions
of the open loop could be (1):
-
A==b
Z o =
Z S =
SS^
2
^
1 mS
mo
+
LL
gZ
gZ
)
)
RC S
R
L
)) + 1
rC S
r
s
SS
)) + 1
+++
-=
Rr CC RC rC
gR rC gR rC
gr gR
10
LS LS LL Ss
h++
mL SL mL Ss
ms mL
.
h
(4)
Subsequently, for the stability of
the function, we have 10A b-= ,
which is calculated in (4) with the
Routh-Hurwitz stability criterion.
Approximately, in Laplace's (4),
SL
&
,
Therefore, all of the poles are on
the right side of the imaginary axis.
IEEE SOLID-STATE CIRCUITS MAGAZINE
SPRING 2022
77
(2)
(3)
(1)
if rR the function is stable.
IEEE Solid-States Circuits Magazine - Spring 2022

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