IEEE Solid-States Circuits Magazine - Fall 2020 - 118

equated to 23 dBm within a 180-kHz
bandwidth. A typical output spectrum can be observed in [7], where
the main nonideal components are
the image, third-order counter intermodulation (CIM3), and local oscillator leakage.
A corner case of LTE band 13
shows that the CIM3 falls in a public
safety band that serves the missioncritical communication needs of
first responders charged with the
protection of life and property, such
as police, firefighters, and emergency medical services. Therefore,
stringent conditions are imposed on
the CIM3, particularly for a SAW-less
design. A Fourier series of a square
wave illustrates the presence of a
strong third harmonic, which can be

4G Rx Single-RB Transmission
and Its Impact

the so-called carrier aggregation
technique can be applied. During
the lecture, an appropriate Rx architecture was presented (see Figure 6). Yet some coexistence issues
arise in band 7. The secondary
component of the voltage-controlled oscillator (VCO), interacting
with the Tx primary component
leakage, degrades the overall signal-to-noise ratio, requiring the
multimodulus frequency planning
of the VCO.

Transmit Linearity

5G Motivation for the Phase Array

Physically speaking, the LTE band
is, at its maximum, 20 MHz; the
applied modulation determines
the downlink capability. In view of
increasing the Rx downlink speed,

A 5G New Radio (NR) mm-wave prototype [9] was presented during the
2017 International Solid-State Circuits Conference (ISSCC). The key
takeaway was that mm-wave antennas are small, as demonstrated in
Figure 7. The prototype, which was
the size of a smartphone, hosted
three antenna modules with 12 antennas, in total. Multiple-antenna
modules help enhance the spatial
coverage, although several phasedarray modules are needed within
a single phone. A key metric is to
minimize the insertion loss after
the power amplifier to improve efficiency and thermal performance.
From the system perspective, this
opens a plethora of new and yet to
be explored architecture opportunities, from the monolithic chip to
multiple dies.

canceled using a harmonic-rejection
waveform on the mixing process, a
well-known technique presented in
[8]. Additionally, the drive amplifier
is known to be an important contributor to the CIM3, as is the power
mixer proposed in [7] and presented
in Figure 5. Both enable a stringent
reduction of the CIM3 presence in
the output spectrum.

RFOUT

Matching_Network
Gain_Control
QUAD
GM_I

LOI

LOI
-

Summary and Discussion

FIGURE 5: The power mixer architecture for eliminating CIM3.

SP3T

PLL1

Rx
SAW

LNA1

Rx
SAW

LNA2

Rx
SAW

LNA3

PLL2

Contiguous Intraband

LNA1

PLL1

Noncontiguous Intraband

LNA1

PLL1, PLL2

Noncontiguous Interband

LNA1, LNA2

PLL1, PLL2

Active Blocks

FIGURE 6: The carrier aggregation Rx architecture. PLL: phase-locked loop.

118

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IEEE SOLID-STATE CIRCUITS MAGAZINE

The WebEx presentation was the
Chapter's second since the beginning of the pandemic. The smartphones in our pockets carry ~30
years' worth of RF/analog circuit innovation. Each standard generation
brings a new set of challenges. The
architecture has to be backward
compatible. A multimode/multiband cellular-equipped transceiver
targeting 5G NR still has to support
all 2G circuit specifications.
There is no globally " optimal "
Tx/Rx architecture. High-level constraints, such as transceivers targeting
handsets for global roaming versus country-specific service and the
smartphone-versus-feature-phone

IEEE Solid-States Circuits Magazine - Fall 2020

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