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HIGH-PERFORMANCE MILLIMETER-WAVE AND TERAHERTZ DESIGN, A NEW APPROACH TO DESIGN ABOVE FMAX/2

Author
Khatibi, Hamid
Abstract
All promising applications of terahertz (THz) and millimeter-wave (mm-wave) systems,
from imaging and spectroscopy to high data-rate communication, necessitate the design
of high efficiency signal sources and amplifiers. In addition to the high propagation loss
of the signals in these frequency ranges, the poor activity of the existing CMOS/SiGe
devices working above fmax/2 emphasizes on the importance of developing new design
methods in order to have high output power and efficiency signal sources and high power
gain amplifiers.
Despite of these challenges in circuit design at this frequency range, the myriad applications
of the systems working in this frequency range has attracted many researchers
to work on these systems. In the past ten years, the reported output power of signal
sources in this frequency range has increased by more than 40 dB which is a huge
progress. High frequency amplifiers have also passed through a tremendous progress
during the past decade. However, generating sufficient power is still one of the critical
issue in these systems. Indeed, the so-called “terahertz gap” is a quite well-known fact,
which means both silicon based electronics and photonics based devices are incapable
of generating adequate power in the mm-wave and terahertz frequency range. Thus, the
researchers have to come up with new methodologies to increase the output power. This
main challenge presents itself in designing two fundamental circuit blocks that appear
in most electronic systems and circuits, i.e. the signal sources and the amplifiers. Compared
to low frequency, the former lacks high DC-to-RF efficiency and the latter suffers
from a low power gain.
Chapter 1 provides a complete overview of progress and challenges in mm-wave and
THz signal source design. In Chapter 2 a novel approach to design efficient high-outputpower
fundamental oscillators beyond fmax/2 of the employed process is presented. The
idea is to shape and maximize the unilateral power gain of the network at the desired
frequency using optimum passive internal and external feedback networks. The proposed
technique significantly improves the output power and DC-to-RF efficiency of
the oscillator. To show the feasibility of this novel approach, a 175 GHz fundamental
oscillator is designed in a 130 nm SiGe BiCMOS process (fmax ' 280 GHz), which
achieves a measured DC-to-RF efficiency of 11.7% that is one of the highest ones among
all previously reported oscillators above fmax/3 of their active devices. Measurements
show that the designed oscillator generates a peak power of 3 mW (4.8 dBm) with a
phase noise FoM of -195.4 dBc/Hz at 1 MHz offset frequency, which is the highest
phase noise FoM among all reported CMOS/BiCMOS mm-wave and terahertz oscillators.
The proposed method takes into account the possible PVT variations as well as
modeling errors of the passive components in the design stage. A similar approach to
design efficient high-output-power fundamental oscillators close to the fmax of the employed
process is presented in Chapter 3. The idea is based on shaping and optimizing
the maximally efficient power gain (GME) of the circuit using a pair of internal/external
feedback mechanisms. Solving a constrained optimization problem, an optimum pair of
passive feedback network is designed to achieve the highest maximally efficient power
gain in order to increase the output power and thence the DC-to-RF efficiency. A 195
GHz fundamental oscillator is designed in a 55 nm SiGe process (fmax ' 340 GHz),
which achieves a significantly higher DC-to-RF efficiency (15.3%) among all reported
oscillators working above fmax/3 of their active devices. The oscillator generates a peak
power of 4.5 mW (6.5 dBm) with the best phase noise of -82.3 dBc/Hz and the best FoM
of -197 dBc/Hz measured at 100 KHz offset frequency, which is the best phase noise and
FoM among all CMOS/SiGe mm-Wave oscillators. The proposed optimization-based
method takes into account PVT variations as well as modeling errors of all components
in the design process to guarantee the functionality of the fabricated circuit.
The last two chapters address the challenging problem of designing high power gain
amplifiers at mm-wave and THz frequency ranges. A novel theory of stability for twoport
networks is developed in Chapter 4. Using this theory, a new method of designing
amplifiers with high power gain working close to the maximum frequency of oscillation
(fmax) is proposed. Contrary to the existing amplifier design methodologies, in
this method the transistor capability of power amplification is fully utilized. This becomes
more important at frequencies close to the fmax where having high power gain
is challenging due to degraded activity of the employed device. The proposed method
considers the modeling errors and process-voltage-temperature (PVT) variations of the
employed components in the design stage to ensure that the fabricated amplifier will be
stable with a decent power gain even if the worst case variations and modeling errors
happen. To show the feasibility of the proposed approach, a three-stage amplifier at 173
GHz, using BJT’s from a 130 nm SiGe process is designed. The fabricated amplifier
has a maximum measured power gain of 18.5 dB at 173 GHz which achieves highest
defined power gain FoM among all reported state of the arts.
Chapter 5 proposes a new approach to design a mm-wave high power gain cascode
amplifier. The gain is enhanced by adjusting the size of the cascode transistor together
with a desensitized inductive impedance at its base. The impedance at this node has a
critical role in determining both gain and stability. The employed desensitization technique
decreases the effect of process variations and modeling errors on this impedance
which results in a reliable design. Providing enough degrees of freedom, this method
results in a conjugate matched input and output impedances. Therefore, two or more
of this stage can be simply cascaded to get higher gain with no need for an inter-stage
matching network and hence no additional loss and gain degradation. Based on this
approach, a single stage amplifier at 183 GHz is implemented in a 130 nm SiGe process
which has a power gain of 9.5 dB, 3 dB bandwidth of 8.5 GHz and saturation power of
-2.8 dBm.
Date Issued
2017-08-30Subject
Electrical engineering; mm-wave; fmax; Phase noise; THz; oscillator; amplifier
Committee Chair
Afshari, Ehsan
Committee Member
Apsel, Alyssa B.; Molnar, Alyosha Christopher; Pollock, Clifford Raymond
Degree Discipline
Electrical and Computer Engineering
Degree Name
Ph. D., Electrical and Computer Engineering
Degree Level
Doctor of Philosophy
Rights
Attribution 4.0 International
Rights URI
Type
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution 4.0 International