Chapter 13
CMOS THz Wireles s
Communicat i on
13.1 Introduction
Due to the significant increase of mobile data in recent years, there is an
emerging demand for capacity and speed for the next generation of wireless
network to provide wir eless data rate of several tens of gigabit/s [270]. It
requires developing more spectrum-efficient wir eless transmission with large
bandwidth. A depiction of the evolution of data rate achieved by wireless
system, known as Edholm’s law of data rates [271], is shown in Figure 13.1. It
can be observed that around the year of 2020 the wireless data rate will reach
around 10 0 gps .
A wireless communication system with gigabyte data rate can only be
achieved with an advanced transmission scheme and a modulation metho d
having a s pectrum efficiency of at least 14 bit/s/Hz, which is extremely chal-
lenging for the existing RF or microwave technologies [15]. One approach to
reach that hig h data rate with a spectrum efficiency of few bit/s/Hz is to em-
ploy ultra-high carrier frequency far beyond 10 GHz. Wirele ss links with data
rates of 2Gbps have been recently explored at 60 GHz [272, 39] for wireless
HD but still cannot reach the scalability for the future demand of ultra-high-
definition (UHD) video. Co nsequently, an alternative unregulated spectrum to
achieve ultra-high bandwidth can be found in the sub-THz fr equency range
(up to 300GHz). The short-range (or near-field) sub-THz wireless communi-
cation is currently studied by various research groups such as UC-Berkeley,
Caltech and Qualcomm [273, 274]. The Terahertz Interest Group (IGthz) un-
der IEEE 8 02.15 WPAN was founded in 2008 to develop standards for THz
289
290 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
Figure 13. 1: Development of data rates in wireline, n omadic and wire-
less system s [15].
communications. The main task of the group is working on the spectrum
evaluation and standard draw-up for potential application, such as ultra-high
sp eed and capa city backhaul for cellular communication, THz Nano Cells,
Board-to-Board Communication, etc.
Recently, much attention has come to foc us on point-to-point local-area
wireless technologies within the office or home as well as human-area wireless
communication technologies within human reach. The most successful and
popular near-field (close proximity) wireless technology is IC-card and B lue -
tooth which operate at microwave frequenc y ra nge with limited data rate.
As shown in Figure 13.2(a), many advanced applicatio ns, such as UHD video
downloading and sharing, ultra-high speed wireles s USB, etc., push the data
volume of tr ansmission toward gigabytes and even terabytes. Meanwhile, the
transmitting time is required within seconds for better user experience. This
can be only achieved by operating in s ub-THz regime which offers ultra-wide
bandwidth and a high-speed data rate. The potential applications by such a
near-field THz wirele ss link are illustrated in Figure 1 3.2 (b).
For the current experimental THz communication system, the conventional
approaches to generate a nd detect THz-band radiation include the utilization
of a photonic device. For example, from a THz signal generation perspe ctive,
photodiodes and Quantum Cascade Lasers (QCLs, e.g., GaN, GaAs) [2 75]
have been proposed as high-power THz local oscillators (LO) in a heterodyne
transceiver architecture. Note that QCLs operate at very low (almost cryo-
genic) tempe ratures, and is als o limited by the need for an external laser for
optical electron pumping with lo ts of mirrors and lenses fo r optical path ad-
justment. The whole system is us ually bulky, expensive (SGD 400K ∼ 600K)
and hence difficult for extensive deployment. From the signal detection point
of view, among others, Schottky diodes and bolometric detectors have been
investigated for dir ect detection of terahertz radiation. These devices ar e able
CMOS THz Wireless Communication 291
(a)
(b)
Figure 13.2: (a) Need of near-field wireless communication classified
by data column; (b) potential appellations of a near-field THz big
data rate wireless link.
to detect very low power signals with a modulation bandwidth up to GHz.
Unfortunately, their performa nc e is always degraded when operating at room
temperature. The other approach to g enerate and detect THz-band radiation
includes the utilization of no nlinear optics such as optical rectification and the
linear electro-optic effect, mainly utilized for spectroscopy application [276].
With the rapid development of semiconductor technology, III-V pro-
cess (such as GaAs, InP)-based electronic THz system has the advantage
of compact size compared to photonic solutions. A typical program funded
by DARPA-USA is aimed to achieve terahertz monolithic integrated circuit
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