IEEE Solid-States Circuits Magazine - Fall 2020 - 117

The 3G standard released a new
operating condition, the frequencydivision duplexed system, where
both the Tx and the Rx paths operate at the same time but at different
frequencies. This implies the use of
a duplexer ahead of the paths. Given that, at a finite isolation level, it
is possible for the duplexer in the
Tx path to leak into the Rx path,
most circuit techniques had to add
a dedicated filter in the path despite
the mask imposed by the 3rd Generation Partnership Project.

4G Tx Single-Resource-Block
Transmission and Its Impact on
Transmit Linearity
When smartphones came into the
short but intense history of mobile
telephony, they shifted traditional
voice calls and text messaging toward compact applications requiring high data rates and low latency,
challenging the network infrastructure. The concept of resource blocks
(RBs), each 180 kHz wide, was introduced. The Tx could, then, fully
use an RB of a given band in cases
where the power was distributed
at 6 dBm or concentrated, which

3G Rx Multimode Oscillators
In comparison to the 2G system, the
phase noise specification was sig-

5
Average (NMOS and PMOS) Voltage (V)

Supply Voltage
Threshold Voltage

From the Rx perspective, the reference sensitivity level is defined at
-102 dB referenced to 1 mW (dBm)
by the standard [5]. A 2G-compliant Rx must be able to withstand
blockers defined by a band-specific
blocking profile while receiving a
desired Gaussian minimum shiftkeying modulated signal at 3 dBm
a b ove t he r efer ence sen sit ivity (-99 dBm). It can be distinguished between in-band and
out-of-band blocking profiles, as
shown in Figure 4.
The in-band blocker is located at
an offset of 3 MHz from the carrier
and defined at -23 dBm. That is 76 dBm
above the signal, and the out-of-band
blocker is at 0 dBm, which is 99 dBm
above the signal. In these conditions, the Rx chain gets constrained
to w it hst a nd r ough ly 10 0 dBm
without a compression point above
0 dBm. Originally, a surface acoustic wave (SAW) filter was placed
ahead of the reception to suppress
the 0-dBm blocker by 20 dB to prevent the low-noise amplifier (LNA)
from saturating, at the penalty of
adding noise. A second approach,
called the SAW-less Rx, slightly relaxes the noise figure requirement
but imposes a highly linear LNA.
Bhagavatula then presented a few

3G Tx Coexistence

1,
0

2G Rx Without a Surface
Acoustic Wave Filter

nificantly relaxed for the local oscillator. Since backward compatibility
is required within the standard, solutions, such as the multimode oscillator [6], were meaningful.

architectures published within the
scope of the SSCS.

FIGURE 3: Core supply voltage and threshold voltage scaling with the node geometrical
scaling.

0
Power (dBm)

processes and the clock swing reduces. Thus, it becomes increasingly challenging to achieve a low
phase noise.
The core voltage and threshold
voltage scaling are illustrated in Figure 3. The data set is based on IEEE
Electron Devices Society publication
data, which are available in [4] and
can be updated with the collection of
new data points. The plot shows that,
mostly below 90-nm technology,
the core voltage is lower than 1.2 V,
which was shown in [3] to be a critical
voltage supply boundary for achieving the phase noise specification.
During the lecture, several circuit
techniques were considered to meet
the phase noise requirement despite
the challenging voltage scaling.

20 M

-23
3M
-99
100,000

905

RF
980
Frequency

12.75 G

FIGURE 4: The 2G standard blocking profile.

IEEE SOLID-STATE CIRCUITS MAGAZINE

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IEEE Solid-States Circuits Magazine - Fall 2020

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