IEEE Solid-States Circuits Magazine - Summer 2021 - 36

The modulation scheme plays an important role
in the required specifications of a receiver and
hence its power consumption.
modulation [6]. Other solutions use
a passive mixer-first approach to
reduce the number of power-hungry
RF components while adding some
level of selectivity through downconversion
and high-Q baseband
filtering [7] and frequency hopping
[8]. Mixer-first solutions have demonstrated
exceptional SIRs, with
submilliwatt active power.
100,000
10,000
1,000
100
10
1
ULP Receiver Adoption
The modulation scheme plays an
important role in the required specifications
of a receiver and hence its
power consumption. Figure 7 shows
that coherent communication [e.g.,
binary phase-shift keying, orthogonal
frequency-division multiplexing
(OFDM), and quadrature amplitude
modulation] requires significantly
higher power to demodulate. All
modern wireless standards use some
form of coherent modulation for better
spectral efficiency. Noncoherent
modulation, such as OOK, frequencyshift
keying, and pulse position modulation,
is used exclusively for ULP
receivers. This creates a gap between
standard-compliant radios and stateof-the-art
ULP receivers.
Wireless standards are being mod0.1
0.01
0.001
0.0001
Slope
= 1
10× Rate = 10× Power
0.01 0.1 110 100 1,000 10,000 100,000
Data Rate (kb/s)
FIGURE 5: ULP receivers tend to be practically limited to peak data rates of 1 Mb/s, and the
data rate trades with the active power as expected.
ULP Radios Published 2005-Present
100 m
10 m
1 m
100 µ
10 µ
1 µ
100 n
10 n
1 n
0.1 n
-80
-60
-40
SIR (dB)
All Radios Standard Compatible Radios
FIGURE 6: Interference is a challenge for ULP receivers, with many not reporting a measured
SIR. RFIC: IEEE Radio Frequency IC Symposium; JSSC: IEEE Journal of Solid-State Circuits;
CW: continuous wave.
36 SUMMER 2021
IEEE SOLID-STATE CIRCUITS MAGAZINE
-20 020
2019 RFIC
JSSC, 2019
(Frequency
Hooping)
ified to incorporate ULP receivers as
wake-up radios to reduce the energy
spent on synchronization. The IEEE
working group for Wi-Fi created the
802.11ba task group to investigate
adding a wideband OOK message to
the 802.11 base standard. The OOK
message is embedded in a standard
Wi-Fi packet and can be generated
with existing transmitters only after
a firmware update. It can be demodulated
with a ULP companion receiver
that has an active power of <100 µW
[9], [10]-more than 100× less power
than a fully compliant Wi-Fi radio. A
Bluetooth special interest group is
also looking at adding a wake-up message
to the next version of the standard.
Hopefully, more details on this
will become publicly available soon.
The 3rd Generation Partnership
High Interference
Rejection is a Challenge
for ULP Design
2019 RFIC (CW)
JSSC, 2019 (CW)
Only 43 Out of 179 Low-Power
Receivers Report SIR
Project introduced a wake-up message
for the NB-IoT in release 15 of
the cellular standard. The NB-IoT
uses OFDM with 12 subcarriers and
quaternary phase-shift keying modulation,
which inherently is not low
power to demodulate. In release 15,
NB-IoT paging events are preceded
by a wake-up signal, which is a
unique correlation-based OFDM
Zadoff-Chu sequence that somewhat
simplifies receiver implementation,
resulting in lower power but not yet
ULP [11]. The significant advantage
Power (W)
Power (µW)

IEEE Solid-States Circuits Magazine - Summer 2021

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