IEEE Solid-States Circuits Magazine - Fall 2020 - 69

Frequency

1

0

1 MHz

fc4

1

0

fc3

1

0

fc2

1

fc1

1
Data

1
1 µs

2 µs

3 µs

4 µs 5 µs
Time

6 µs

7 µs

8 µs

FIGURE 4: The frequency agility-based countermeasure: an ultrafast bit-level FH scheme
with 1ns-hop periods leveraging the frequency agility of BAW resonators [6].

104

[12]

[11]

103
102
101
100

[13]
0.1

nJ

101

[10]

[16]

[15]
[14]
[17]

1n

J

100
10

Crystal
PLL

nJ

nJ

102
103
Start-Up Time (µs)

104

FIGURE 5: The start-up time and power performance of state-of-the-art crystal oscillators
and PLLs [7].

(1)

To satisfy the condition of fBB, step
1 TfBAW,
fBAW TfBAW
2
	
(2.440 GHz) (4.6 MHz)
= 75 MHz
2
(2)

fBB, N 1

=

Preamble

for the multichannel coverage. One
way to improve the range is to per-
form quadrature mixing with upper
sideband (USB) and lower sideband
(LSB) selection. The quadrature mix-
ing decreases the single-sideband
coverage of fBB, N to 53 MHz, but the
double-sided available bandwidth
coverage becomes 106 MHz, result-
ing in a greater coverage than the re-
quired ISM band coverage.
The tunable RF (fRF ) synthesized
by the multichannel BAW Tx architec-
ture is given by fRF = fBAW ! fBAW /4N,
where the ± is determined by the

USB or LSB selection and the integer
divide ratio of N. This integer divide
ratio is programmed into the divider
in real time. A linear baseband filter
is required to limit the in-band spurs
in the final output spectrum to below
the BLE requirement of -30 dBm.
Time interleaving for avoiding dead
zones. Time interleaving is utilized
in this work to avoid the dead zone
associated with the settling time of
the baseband circuits, e.g., the set-
tling time of the low-frequency filters
required for the in-band spur sup-
pression. Each Tx path delineated in
Figure 8 achieves multichannel cover-
age in the ISM band using the frequen-
cy synthesis technique from a single
BAW resonator. They are combined
through a time-interleaved mixer cir-
cuit that alternates the active Tx path
for data transmission. Time interleav-
ing, presented in Figure 9, allows the
baseband frequency settling of the in-

2.4-GHz ISM Band
Impedance (arb.)

	

fBB, step = fBB, N - 1 - fBB, N =

fBAW
fBAW
.
2N
2 (N - 1)

fc5

Start-Up Power (µW)

2.421, 2.480, and 2.491 GHz. To cover
the entire Industry, Science, Medicine
(ISM) bandwidth of 80 MHz, ranging
from 2.4 to 2.48 GHz, a multichan-
nel coverage BAW-based Tx [7] is ar-
chitected, achieving bit-level FH at a
1-ns hop period while overcoming
the limited tuning range of a single
BAW resonator.
Frequency synthesis from a single-BAW resonator for multichannel coverage . A fast-start-up and
low-power Tx architecture features
a single in-band BAW resonator in
both time-interleaved Tx paths and
achieves wide-frequency coverage,
as displayed in Figure 7. For full ISM
band coverage, larger step offsets are
generated by mixing the output of a
programmable integer-N divider with
the original BAW frequency, fBAW, at
2.44 GHz, located in the middle of the
ISM band [6], [7]. Frequency channels
between the divider steps should be
covered by the tuning range of the
BAW, TfBAW = 4.6 MHz.
The frequency separation (fBB, step)
between the divider steps of N (fBB, N )
and N - 1 (fBB, N - 1) is given by

1,000
100

Loading +
Tuning

Unloaded

10
1

< 4.6 MHz

2,400
2,450
2,500
Frequency (MHz)
FIGURE 6: BAW resonators have a limited continuous tuning range of roughly 4-5 MHz [7].

active Tx path with 1-ns hop periods
while the concurrent transmission
takes place on the active path.

Cryptographically Secure, DataDriven Dynamic Channel Selection
The modulation-based attack is
mitigated by developing a crypto-
graphically secure (CS), data-driven
dynamic channel selection scheme

	 IEEE SOLID-STATE CIRCUITS MAGAZINE	

FA L L 2 0 2 0	

69
IEEE Solid-States Circuits Magazine - Fall 2020

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