IEEE Solid-States Circuits Magazine - Fall 2022 - 30

VDD
Output
Network
Matching
Network
VDD
Output
Network
RFF1 RFFn
Vin
Enabled
Drivers
EN[0:N-1]
Output With
Configured
Fingerprint
Time-Stamped
Fingerprint
(a)
13 57 911
02 46 810
t1
FIGURE 2: (a) The high-level structure of the reconfigurable PA and (b) the sliced transistor elements that are used to imprint configurable RF
fingerprints on BLE packets.
baseband models can be evaluated.
The work was validated using a lightweight
CNN classifier, which demonstrates
the preservation of relevant
RF fingerprint features within it.
The following section describes
the structure of the reconfigurable
PA and the measurement setup used
for collecting the dataset. The section
" Recorded Data Analysis " analyzes
the recorded signals, and the
section " CNNs for PA Configuration
Classification " presents the implementation
of the CNN classifier. The
section " Environmental Changes "
discusses the impacts of the environmental
changes, and the final section
concludes the article.
Reconfigurable PA
and Dataset Collection
Reconfigurable PA
The high-level structure of the reconfigurable
PA used for this study is
illustrated in Figure 2(a). The primary
PA transistor is sliced into several
parallel devices that may be enabled
independently of one another through
their driver circuitry, as shown in Figure
2(b). Each transistor is operated as
a switch and is connected to a single
Class E PA-style output network that
blocks higher order harmonic components
from reaching the output while
shaping the transistor current and
voltage waveforms to lower power
Selectable
Elements
Output
Network
Technology
Chip Area
Core Area
Set Number of
Choosing 9
From 12
1 mm
FIGURE 3: A die photo of the reconfigurable PA used to collect the data.
30
FALL 2022
IEEE SOLID-STATE CIRCUITS MAGAZINE
65-nm CMOS
1 mm2
0.267 mm2
220
dissipation. The total off-capacitance
present at the output network as
a result of the transistor parasitics
remains constant irrespective of PA
configuration, permitting configuration-independent
operation.
At the time of fabrication, each
selectable slice's transistor parameters
(, )VTH b are affected by random
process variations in accordance with
Pelgrom's law [11]. Because these
transistor parameters ultimately give
rise to the PA's RF fingerprint, selecting
different combinations of PA
device slices results in distinct RF
fingerprints. A design with 12 total
selectable slices was designed for a
frequency of 2.4 GHz and taped out. A
die photo of a fabricated chip sample
is shown in Figure 3. To maintain a
balance of output power and configurability,
it was decided to enable nine
slices at a time to allow a combinatorial
search space of C (12,9) = 220 possible
PA configurations.
Bluetooth Low-Energy
Packet Parameters
A physical-layer waveform corresponding
to a nonconnectable
advertising packet, such as those
used for transporting BLE Mesh protocol
data units, was generated using
tn
EN[0:N-1]
(b)
Selectable PA
Elements
Vin
1 mm

IEEE Solid-States Circuits Magazine - Fall 2022

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