LO Generation and Frequency Division at mm-Wave and Sub-Terahertz Frequencies

Abstract

This Thesis presents the design and investigation of high-frequency fundamental
VCO(Voltage controlled oscillator) and injection-locked frequency dividers (ILFDs)
for millimeter-wave (mmWave) and sub-terahertz (sub-THz) communication
systems. A magnetically tuned voltage-controlled oscillator (VCO) and magnetically
tuned ILFD pair are proposed for sub-THz applications. The 140 GHz
fundamental VCO achieves a phase noise of −100.6 dBc/Hz at 10 MHz offset
with a figure-of-merit (FOM)-178 dBc/Hz at 10 MHz with a tuning range of 6.43
%. while the ILFD covers 133–154.5 GHz with a locking range of 18.12 % and
total power consumption of the pair is 7.2 mW. Additionally, a 200 GHz divideby-
two ILFD is demonstrated, covering 186.5–224.5 GHz with a locking range of
19.34 % and consuming 4.2 mW. The circuits operate with a 1.2 V supply and
are implemented in a 65 nm CMOS process, with simulations conducted in Cadence
Virtuoso. The limitations of the current design and potential improvements
are discussed, highlighting its applicability for future 6G mmWave and sub-THz
transceivers.

Popular Abstract

At the heart of future wireless systems such as 6G lies the push toward extremely
high frequencies, extending into the sub-terahertz (sub-THz) and terahertz (THz)
range. These frequencies promise ultra-high data rates and the ability to support
emerging applications such as immersive communication and high-resolution sensing.
However, moving to such high frequencies is not just a simple extension of
today’s radio technology—it introduces a completely new set of challenges. At
lower frequencies, such as sub-6 GHz and even millimeter-wave bands, modern
transceivers rely on well-established architectures that combine amplifiers, mixers,
and local oscillators to transmit and receive signals efficiently. As frequencies approach
the THz range, these conventional approaches begin to break down. Semiconductor
devices struggle to provide sufficient gain, power efficiency drops, and
noise performance degrades significantly. As a result, signals attenuate quickly,
limiting communication distances unless advanced techniques are used. In particular,
ultramassive numbers of antenna elements must be combined coherently
with sharp beamforming, with thousands to tens of thousands of antenna elements
potentially required for THz base stations. One of the key challenges in these systems
is the generation of stable and low-noise signals at extremely high frequencies.
Instead of distributing a single high-frequency signal across a chip—which would
consume excessive power—engineers increasingly rely on distributed architectures,
where many local oscillators operate in parallel. This approach improves scalability
but also introduces new challenges, such as maintaining coherence and controlling
phase noise across the system.
This thesis focuses on addressing some of these challenges through the design of
a sub-THz voltage-controlled oscillator (VCO) and an injection-locked frequency
divider (ILFD). The VCO is responsible for generating high-frequency signals,
while the ILFD enables efficient frequency scaling and improved phase noise performance.
By carefully designing these building blocks, it becomes possible to
generate and manipulate high-frequency signals more efficiently, which is essential
for future large-scale systems. The work contributes to ongoing efforts to make
sub-THz and THz communication systems practical. While significant challenges
remain, advances in circuit design—such as the techniques explored in this thesis—
are key steps toward realizing the high-speed, high-capacity wireless networks
envisioned for the next generation of communication technologies.

• author: Krishnan, Avinash
• supervisor: Henrik Sjöland
• organization: Department of Electrical and Information Technology
• course: EITM02 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• report number: LU/LTH-EIT 2026-1128
• language: English
• id: 9231124
• date added to LUP: 2026-06-09 13:43:43
• date last changed: 2026-06-15 01:42:36