Personal Statement
Hongjiang Li
In 2008, atop nearly 300 000 other students in the National College Entrance Examination, I was
admitted to the electronic engineering department of Tsinghua University. Here I got the chance
to absorb the classic as well as the fresh ideas with so many genius peers. In sophomore year, I
design a smart shopping cart by using an MCU to control a RFID chip, aiming to reduce the
unbearable waiting time at the cashier in the supermarket. Though I was extremely excited when
I saw the cart functioned properly at first, I was not satisfied with writing C programs to control
the chip, rather I am thirsty to know what magic on earth are there in this tiny 1 cm2 black chip.
How does it operate? What is behind the invisible radio frequency wave? This aspiration led me
to choose microelectronics as my major in junior year.
Driven by this strong enthusiasm, I was the only one in junior year who chose all circuits-related
courses our department offered, even including the Principle of Microprocessor designed for
senior students. Though met with heavy workload, the finishing of the Marathon Competition
lent me confidence to tackle all the obstacles I met. I finished every course project with 100
percent effort and patience, all of which won A or A+. Especially in the project of the course
Digital Integrated Circuit Design and Analysis, the critical path latency of my 32-bit adder was
only 355 ps, ranking the fastest. This true love to the field also enhanced my third year’s GPA to
90. Meanwhile, I participated a Student Research Training program to design and simulate a
spread spectrum clock generator using hybrid controlled oscillator. The training process opened
the first door of analog/mixed signal circuit design to me, encouraging me to explore more
beauty of this area.
Last summer, I dive into the research of NoC, a trend of future integrated systems -- parallel
computing with multi-cores. When dealing with the key issues of application modeling, mapping
and scheduling, most previous simulator use simplified IPcores running ideal applications which
are far away beyond the actual traffic. I designed and developed a simulator whose IPcores at
each tile can be practical ARM,DSP,DMA models etc. An arbitrary traffic pattern can be
implemented by loading programs to those cores. Thus it can verify different mapping models
and algorithms even including run-time mapping and management, providing reasonable and
accurate solution evaluations.
While doing the project of the simulator, I was inspired by the idea of SoC(System on Chip).
Especially, the wireless communication SoC caught my eye. I switched to Professor Yu’s group
and started the design of transceivers for next-generation 802.11ac WLAN standard. As
integrating VCOs into RF transceivers with standard CMOS technologies is usually one of the
most challenging design tasks due to the fact that critical parameters like large frequency tuning
range, low power consumption and low phase noise must be considered carefully and the fact
that all these parameters are primarily determined by the passives used in VCO circuits, I finally
chose Transformer-based Quadrature Voltage Controlled Oscillator modeling and design as my
degree thesis. Though as an emerging solution to wide tuning range VCOs, little research work
focused on the thorough RF transformer modeling and analysis. Firstly, based on the previous
work using magnetic LC tank, I have proposed a novel QVCO architecture using PMOS
cross-coupled transistors to perform Q signal and NMOS to perform I signal, thus reducing the
current source effective noise contribution as well as power consumption. Furthermore, by
deriving a complete RF transformer model concerning its inductance, mutual inductance, quality
factor, noise figure and other related parameters, I will analysis the how figure of merit(FOM)
would be changed when adding the transformers in the circuits. Most importantly, I expect to
find a complete and easy procedure of the transformer design, simulation and implementation.
UCSD ECE professors attract me by their distinguished achievements in electronic circuits and
systems. Among them, I am particularly interested in Dr. Lawrence E.Larson’s Radio Frequency
Integrated Circuits Group because with my relevant experience in oscillator, clock generator
design as well as ongoing passive inductors modeling thesis, I hope I can contribute to the new
transceivers design by using power-combining techniques and exploiting the digital device
properties. Also, I am equally interested in professor Bang- Sup Song’s research on high speed
ADC/DACs because my related experience of designing an ADC in course IC Design Project.
During my graduate study, I would like to focus the following topics:
1. The need for high performance on-chip passives including inductors and varactors in RF
technologies has become increasingly important due to the technology and integration
requirements of high functionality and low cost RF circuit applications. I would like to have a
further and deeper understanding on the integrated inductors based on my current degree
thesis work. I aim to establish a complete model of describing the impact of passive
components to the transceivers under PVT variations.
2. As the need for lower power consumption, lower noise and lower cost are still the priority
concern in today’s RF transceivers, I expect to research on the issue of protection against
electrostatic discharge and optimization of physical design to minimize parasitic impedances.
Just like reconfigurable processors, reconfigurable RF transceivers in a software-defined ratio
may be a promising solution to meet the higher requirement of those aforementioned
concerns and I would love to explore more in that field.
3. As A.Abidi pointed out in ISSCC 1998, “Analog design is now little of the rarefied art of
manipulating transistors into interesting and sometimes useful configurations”, the focus of
microelectronics research is becoming more application-driven. Wireless Body Sensor
Network(WBSN) is becoming a hot issue these days due to the concern to our health. This is
an intriguing area that may greatly change our lives. If I could have the chance, I intended to
make more innovations on the sensor transceivers design.
Undergraduate as I am, I never stopped exploring my dream field as well as myself. I choose RF
circuits design as my major research direction. I believe my relative experience will accelerate my
research in this appealing field and finally fulfill my goals in UC SD