Fatma Almajadub, Khaled Elleithy and Azza Shaer
Department of Computer Science and Engineering
University of Bridgeport
Bridgeport, CT, USA
firstname.lastname@example.org , email@example.com, firstname.lastname@example.org
In this Paper, we enhance the performance of
Wireless Sensor Networks (WSNs) by optimizing the
Wake-up capabilities within a passive radio-triggered wake-
up circuit and then used its applications to manage the
power consumption of the WSNs. The architecture of our
proposed circuit manages the radio power consumption of
WSN by harvesting energy from the radio signals and
making the radio-triggered hardware sends a wake-up signal
to the microcontroller (MCU) of the node. This harvest
process takes only 15μs or less to produce wake-up signals
within the wake-up circuit and prolongs the lifetime of the
WSN nodes. In addition, the proposed circuit receives the
RF signal of the network controller through the antenna
node and produces an output voltage (VOLDC) by its
rectifier module so that this voltage produces direct current
DC of 250 mV with the received power of 0.85uW (-
13.85dBm). Most importantly, the proposed circuit can
produce an output triggered voltage (VOLTG) by its module
of LTC1540 –Nano-power Comparator which works as an
amplifier (VOLDC) and only needs 0.3μA of energy for the
setting of the threshold detector value within the long
distance of 100m or more and radiation source of 2W in
free-space. The simulation results demonstrate that the
proposed circuit can produce VOLDC and VOLTG to trigger
the wake-up signal of MCU within the long distance and
low duty cycle as well as this circuit can identify the
synchronization on WSNs.
Keywords: (WSNs) Wireless Sensor Networks, Passive
Radio Trigger, Wake-up Circuit Capabilities, Low Power
Since the radio transmission consumes most of the power
in WSNs, good management of the radio triggered
capabilities in WSN is the best way to optimize its
performance. However, the main challenge is to optimize
passive radio triggered wake-ups capabilities; especially by
optimizing the wake-up mode or sleep mode in order to
reduce power consumption and cost of WSNs. Due to the
increasing need of radio trigger capabilities on WSNs and
its support by recent techniques, the sensor data can be
derived anywhere on WSNs through several simple and
cheap ways. These are provided by each node on WSN
during sensing, storage, processing and communication
Many studies and researches of WSNs have shown that it
is difficult to replace the batteries of sensor nodes. Thus,
effective management of power consumption in WSNs is
necessary for prolonging the lifetime of WSNs. Therefore,
good power consumption management schemes can be
implemented by exploiting wake-up and sleep schedule
techniques in order to reduce the power consumption of
nodes. Moreover, it is important to synchronize the received
messages of the sensor nodes so that they are received only
when the sensor nodes are in Wake-up mode.
There are many schemes to manage the power
consumption of WSNs over radio trigger capabilities.
Among those techniques that show good performance and
serve our proposed work are the following techniques:
1) Wake-up and sleep schedule scheme .
2) A Stand-Alone Radio Receiver Wake-up scheme
3) A Passive Radio-Triggered Wake-up Circuit Scheme.
2. The Concept of Passive Radio-
Triggered Wake-up Circuit
This circuit consists of a set of diodes, capacitors, and
inductors. The circuit is designed for the realization of the
functions of the wake-up/sleep schedules so that this circuit has the
ability to convert the input power of radio frequency signal (RF) to
the voltage of direct current (DC). In addition, this circuit is based
on the idea of the stand-alone radio receiver wake-up scheme so
that this circuit can activate and shut down the nodes depending on
a wake-up signal in the environment of WSNs. Therefore, this
circuit can eliminate some wake-up periods which waste energy
2.1. WSNs System within the Passive Radio-
Triggered Wake-Up Circuit:
The WSN within the passive radio-triggered wake-up circuit
must be prepared with nodes and controllers. Figure 1 shows the
structure of the node prepared with the passive radio-triggered
wake-up circuit within WSN.
Advancing Wireless Sensor Networks Performance over Radio Trigger
Figure 1: The Structure of Node Prepared with the Passive Radio-
Triggered Wake-up Circuit within WSN
Figure 2 demonstrates that all nodes of WSN should be
equipped with the same antenna which is linked with the
transceiver device as well as with this circuit. In addition, RF-DC
wake-up circuit sends a DC voltage directly to the microcontroller
MCU of the node to stimulate and trigger the interrupted signal
and wake-up the MCU instantly.
Figure 2: WNSs System within Passive Radio-Triggered Wake-up
One of advantages of this circuit is that it only needs low cost
diodes, capacitors, and inductors. Another advantage, this circuit is
a passive circuit, thus it does not need more energy. Therefore, it is
the best choice for realizing power management in WSNs.
3. Proposed Model
In order to enhance the performance of WSNs over
passive radio-triggered wake-up capabilities, we propose
optimizing the circuit of passive radio-triggered wake-up.
This circuit generally contains a set of modules which are
the antenna, an impedance matching module, and a rectifier
module. However, we try to improve these modules in order
to achieve reasonable performance of the wake-up circuit.
Thus it can be used by the WSNs node to achieve good
power management in order to optimize radio trigger
capabilities. The purpose of the proposed circuit is to
receive RF signals in order to generate maximum input
power of these RF signals and convert them to DC voltage
(VOLDC) in order to produce the desired output voltage.
Thus, this circuit can amplify DC voltage to produce the
output TG voltage (VOLTG) in order to trigger the wake-up
signals of MCU within long distance.
Our proposed circuit is designed to improve its
components separately and to support the long distance
from the network controller to the node antenna. Therefore,
we propose to add another module to the general modules
of this circuit which is LTC1540 – Nano-power Comparator
in order to support the long distances between the network
controller and the node antenna, as well as produce prefect
output voltage at a maximum input power. This comparator
may need extra power supply but it will not affect the whole
circuit. However, without the LTC1540 – Nano-power
Comparator module; the proposed circuit does not need
power supply. To keep the node’s power within the
proposed circuit, we propose to provide external power
supply to only the comparator without adding it to the entire
circuit; thus, it will not share power with the circuit. Figure
3 shows the proposed circuit.
Output Of Trigger signal
to wake up MCU
Figure 3: The Mechanism of the Proposed Passive Radio-
Triggered Wake-up Circuit within its Modules
Each node of the proposed design of the wake up circuit’s
modules is equipped with:
1. Printed monopole antenna to function between circuit
modules and its gain factor which is 0.40-0.63 joule.
2. Two impedance matching circuits by using the zero
bias Schottky diode; which is called HSMS285C
(series pair configuration) and is with SOT-323
Furthermore, we propose the use of the multi-stages
rectifier circuit so that each circuit contains some
components like diodes, inductors, and capacitors which
were used in  and . However, in our design we add
resistances for capacitors in order to join the high voltages
within the proposed circuit and reduce the total impedance
and resistance of the moving current into capacitors.
Therefore, we used two diodes and four capacitors merged
together with two resistances in one circuit. However, the
multi-stage circuit module was proposed in many studies of
radio-triggered wake-up circuits, but each study used a
different design such as in , ,  and . These were
costly designs for the passive RFID tags by adding the
CMOS process. Although the design in  used a cheap
design for the improvement of discrete components, 
doesn’t support the long distances between controller
network and the node’s antenna. Therefore, we targeted to
design our proposed circuit module with the aim of
improving long distances, flexibility, low cost, and prefect
Furthermore, we propose to use the comparator module
type LTC1540 – Nano-power with Reference to LT5400
Comparator . The comparator module on our proposed
circuit achieves the following functions:
1. The comparator can compare the DC voltage of
10mV or more with the threshold voltage.
2. The comparator can produce a high voltage trigger
(VOLTG) to wake-up the MCU of the node.
3. The comparator consumes less energy about 0.3uA;
3.1 The Proposed Impedance Matching
Two impedance matching circuits are used so that each
circuit works as a linear equivalent circuit. We propose to
use the zero bias schottky diode which is called HSMS285C
(series pair configuration) and is with SOT-323 package
shown in Figure 4. This diode helps representing the signals at
small levels. Both circuits have the specifications given in Table 1.
The impedance matching circuit is as shown below in Figure 5.
The capacitors in the multistage rectifier are set to 0.30pF  .
Figure 4: HSMS-285C SCHOTTKY DIODE
Table 1: Specifications of The Linear Equivalent Circuit of the
Schottky Diode” HSMS285C”.
The junction resistance of the diode
The junction capacitance of the first diode
The junction capacitance of the second diode
The parasitic resistance is at the base of the
chip and rep resents the losses in the bond wire
and the bulk silicon of the diode
The parasitic inductance a nd capacitance
caused by the package
The parasitic inductance a nd capacitance
caused by the package
The parasitic inductance a nd capacitance
caused by the package
Figure 5: The Linear Equivalent Circuits Models of the
HSMS285C Schottky Diode
3.2 The Proposed Multi-Stages Rectifier
Each one-Stage rectifier module of our proposed circuit
works to double the output voltage. The proposed one-Stage
circuit contains the following components:
1) Two diodes DD1 and DD2 which are connected in series
so that forward current can only travel from the ground
potential to the positive terminal of the output voltage
VOLout. These diodes allow the forward current to move
in one direction so that they work with other elements of
the rectifier circuit to serve as a passage to the forward
current when voltage is increased by a specific value. In
addition, it helps to fix an alternating current (AC).
2) Four capacitors which work as follows:
i. The first one which called CP1 prevents the DC
current from flowing and streaming into the circuit
and helps the current to flow into CP2.
ii. The second one which called CP2 helps to keep the
charge of the high frequency currents and allows the
high frequency currents to flow into the circuit from
iii. The Third, known as the CP3, receives and keeps the
resulting charge in the circuit.
iv. The fourth one which is called CP4 is for refining,
revising and smoothening the output voltage VOLout.
Therefore, this circuit works as a pump so that CP1,
CP2 and DD1 make up a DC-level like converter or
shifter while CP3, CP4 and DD2 make up a peak-like
detector device as is shown in Figure 4.
3) Two resistors (R1 and R2) are added to be used by the
capacitors for uniting the voltage during the proposed
circuit and for reducing the total impedance by merging
resistances and capacitors together to reduce the voltage
on capacitors to zero.
VOLcp1 = VOLcp2 = VOLcp3 = VOLcp4 =0 …..(1)
Thus, the current (Au) equals the voltage of circuit (VOLDC)
divided by the total resistance (R1+R2).
Au= VOLDC / (R1+R2) …..(2)
And capacitance (Cap) equals 1 divided by the total
Cap=1 / (R1+R2) …..(3)
Figure 6: Show The One-Stage Rectifier circuit.
These kinds of rectifiers are necessary to design the
proposed circuit. There is a certain amount of voltage that is
necessary to trigger the microcontroller (MCU) of the node
and the voltage of one stage circuit is not enough for it.
Thus, when we change the voltage of the one-stage circuit
from ground level to a DC voltage VOLDC, the output
voltage will be as follows:
VOLout=4*(VOLMax – VOLDio) + VOLDC. ….. (4)
Where VOLMax is the maximum or peak voltage, VOLDio
is voltage on diodes. Therefore, we can form and prepare
the rectifier circuit with multistage by collecting and
combining several One-Stage circuits so that the VOLDC of
each stage will work as the DC reference to next stage.
Hence, VOLout of M stages circuit is as follows:
VOLout = 4*M*(VOLMax – VOLDio) …..(5)
3.3 The Proposed Comparator Module:
The comparator is an important module in our proposed
circuit to support long distance, even though it needs extra
energy (0.3uA) to set the threshold value which is not
severe compared with other devices, such as the amplifier
which needs 10A. Figure 7 shows the 2.9v Vcc threshold
detector circuit of LTC1540 comparator with Nano-power.
The parameters of the LTC1540 comparator with Nano-
power 2.9v Vcc threshold detector are shown on Table 2.
Figure 7: The 2.9v Vcc Threshold Detector.Circuit of LTC1540
Comparator with Nano-Power
Table (2): The Parameter of LTC1540 – Nano-power
Continuous Source Current
Wide Supply Range
2V to 11V
Input Voltage Range
Reference Output Sources
Up to 1mA
3mm x 3mm x 0.8mm
4. Implementation of the Proposed
In this section, we discuss the implementation of the
proposed rectifier circuit.
4.1 Counting the RF Input Power of the
The RF power (PWRF) of RF signal received by the
proposed wake-up circuit within passive radio-triggering by
an impedance matching circuit is either from the one-stage
circuit module or multi-stages circuit module. Thus, the
parameters in Table 3 are used in equation (6).
Table (3): RF Signal Parameters
Sending Power or RF Signal Power
Output1 of power at network controller’s antenna
Output2 of power at node’s antenna
Wavelength of the electromagnetic wave
Distance between the network controller and the node.
Therefore, the PWRF is given by the equation (1)
PWRF =[( PO_cn * PO_an * PW_s *(λ^2)) / (4π* D_rs)] …..(6)
We found that we can increase the input power PWRF by
increasing the distances D_rs. In the simulation, we used
PW_s of 2W. The receiver power starts at 0.85uW (-
13.85dBm) for 915MHz. Therefore, when PO_cn=2dB,
λ=0.6.56,D_rs=100 or more, then PWRF or PW_s=3.4W (-
As result, the input power or RF signal power (PWRF) is at
the maximum level when VOLMax is very low. In addition,
if the PWRF is constant and not changed during the circuit, it
will increase the VOLDC, thus, VOLDio will be too low.
Therefore, using the zero bias Schottky diode
“HSMS285C” is the best choice for multi-Stage rectifier
4.2 Implementing the One-Stage Rectifier
The implementation of the proposed circuit is done by
executing the mechanism of the circuit in Figure 3 and
Figure 6. This circuit includes the RF signal that has two
parts; the negative part and the positive part of the
capacitors. As well as the voltages on these parts, which
will be different; the voltage of positive part is double the
voltage of negative part.
1) If the RF signal is negative and larger than the
voltage into the DD1, the current will pass through
DD1 and leads to move the charge from CP1 to CP2
while the DD2 is turned off. The voltage of the
negative part on DD1 passes CP1and CP2 then to DD1
and moves from CP3 to CP4. The latter is VOLDio1
which is the difference between the maximum negative
part voltage VOLNMax and the voltage on the DD1.
VOLNout = 2*(VOLNMax –VOLDio1) …..(7)
2) If the RF signal is positive and larger than the voltage
into the DD2, the current will pass through DD2 and
will transfer the charge from CP3 to CP4 while DD1 is
turned off. Thus the voltage of positive part on DD2,
which passes CP1and CP2 then to DD2 and to CP3 and
CP4 ; is the difference between the maximum positive
part voltage VOLPMax and the voltage on the DD2
which called VOLDio2.
VOLPout = 4*(VOLPMax –VOLDio2) …..(8)(a)
Figure 8: The One-Stage circuit within the negative part and the
Positive Part of the capacitors
Therefore, the output voltage of one stage circuit (VOLDC)
is equal to the voltage passed in CP1 and CP2 (VOLin).
Adding to the 4 maximum positive input voltage (VOLMax),
and subtracting 4, the turn-on voltage on diode VOLDio is
VOLout= VOLin+ 4*[VOLMax- VOLDio] …..(8)(b)
Where VOLin is the voltage passed on CP1 and CP2 which
according to (1) equal zero, thus;
VOLin= VOLcp1 = VOLcp2 =0.
Therefore, the output voltage of one-stage circuit is as
VOLDC = 4*(VOLMax - VOLDio) …..(9)
4.3 Implementing the Multi-Stage Rectifier
According to equation (9), when we have M stage
circuit, the voltage would be given by (5).
VOLDC = 4*M *(VOLMax- VOLDio) …..(10)
We can analyze and infer the following when we
implement the Multi-Stage circuit:
1. We can add stages to our proposed circuit as it is
required to convert RF signal to DC voltage until the
last RF input voltage is transformed into the right value
2. We can add stages to our proposed circuit only until a
certain level as we mention in the previous point.
Adding more and more stages would lead to wasting
the power and charge in the diodes and capacitors, thus
the circuit with multi-stages will be less efficient.
Therefore, we must determine the number of the stages
that would give us the maximum DC voltage VOLout.
This number should be as far as the function of radio-
triggered wake-up is needed.
4.4 Implementation of the Comparator Module
The implementation of the comparator circuit is done by
executing the mechanism described in Figure 3 and Figure
7. This circuit includes focusing on the DC voltage
(VOLDC) which is produced from the rectifier module. The
comparator module can amplify VOLDC to TG voltage
(VOLTG) to be suitable with the long distance between the
network controller and node’s antenna. However, the
VOLTG is different based on these distances so that the
VOLTG is produced by following:
VOLTG = VOLDC +VOLHYST+VOLREF. ….. (11)
However, we can choose the comparator to operate from
a single supply (2V to 11V) or a dual supply (±1V to
±5.5V) so that it’s hysteresis can be programmed by using
two resistors R1 and R2 as well as the HYST pin. In
addition, each input operates from the negative supply
within 1.3V of the positive supply so that the output stage
of comparator can reach to 40mA continuously.
As result, we infer that eliminating the power supply
glitches is done by eliminating of the cross-conducting
current that occurs normally when the comparator changes
logic states. For long distances application, the LTC1540 is
available in the 8-pin package, but for distance limited
applications, the LTC1540 is available in a 3mm x 3mm x
0.8mm DFN Package
4.5 Implementing the Proposed Wake-up
We determine the following steps to implement the
proposed wake-up circuit within passive radio triggering to
achieve good management of the radio power consumption
on WSN and harvest energy from the radio signals.
1. It provides a wake-up signal to the microcontroller
(MCU) without using power supply from the harvest of
2. This harvest should only take 15μs in order to produce
the wake-up signal within the circuit.
3. Receive the RF signal of network controller by antenna
4. The Wake-up circuit of a passive radio-triggering
should produce an output voltage (VOLDC) by its
rectifier module so that this voltage is produced by a
direct current DC of 250 mV with a received power as
low as 0.85uW (-13.85dBm).
5. The Wake-up circuit of a passive radio-triggering must
produce an output voltage (VOLTG) by its module of
LTC1540 –Nano-power Comparator which works as an
amplifier to amplify (VOLDC). It needs energy only of
0.3uA for the setting of the threshold detector value
within the long distance of 100m or more and radiation
source of 2W in free-space.
5. Simulation Results
In this section, we present the simulation results of the
proposed wake-up circuit. These results include the
optimization of its capabilities and modules. We choose
Matlab software from Mathworks to simulate and
implement the proposed impedance matching module, the
multistage rectifier module and comparator module. The
settings the simulation parameters are given in Table 4.
Table (4): Simulation Parameters
Distance between the network controller and
the node (D_rs)
100 to 180 meters
Maximum simulation time
RF Signal Power
Output power at network controller’s
Wavelength of the electromagnetic wave
Output power at node’s antenna
Time for wake-up circuit
Power of Radio Frequency
PW of 2W
wake-up circuit at Input power PWRF
7.85dBm, 9.85dBm, 11.85dBm and -13.85
Antenna gain factors
Energy of sensor
Stages of circuit
The voltage of diode as SE diode VOLDio
We used the input power of the RF signal of 0.85uW (-
13.85dBm) which is the result of equation (6). From Table (3),
there are some elements that can produce a voltage higher than
other elements of multistage circuit module because these
elements have a higher quality factor. Therefore, we can produce
high output voltage VOLDC by using the multistage circuit with the
elements which are higher VOLMax and quality. We can also
produce a higher voltage with a distance as long as 100m and
transmitted power (PW_s) of 2W or more for 915MHz.
Furthermore, the one stage circuit with good impedance matching
circuit will produce a DC voltage of about 250mV by equation (9),
but for multi-stages circuit module the voltage produced is given
by equation (10). This harvest takes only 15μs for the wake-up
circuit to produce the wake-up signal and prolong the lifetime of
the WSNs nodes. For VOLTG produced by equation (11) we can
infer the following:
1. The resistances match the rectifier circuit module. Four
capacitors should be used to uniform the capacitors’ voltage
and should be able to transform the flowing power and
voltage of the antenna during impedance circuit module to the
rectifier circuit module in order to achieve good impedance
between the antenna and the rectifier circuit module. This
impedance can increase the output voltage as well as reduce
the loss of transmission.
2. The impedance matching circuit module can increase and
amplify the output voltage. Although this increasing is
passive, we can say that the theoretical efficiency of this
increasing with maximum output voltage and power is
achieved with the maximum quality factor.
3. Theoretically, we can argue that when the VOLDio is
neglected, the VOLDC could be double the whole voltage of
the RF signal. On the simulation, we can’t neglect the
resistance of the capacitors CP1, CP2, CP3, and CP4 which
makes the voltage of each capacitor equal to zero, thus; the
value of the real output voltage VOLDC should be less than its
theoretical value. The proposed circuit should be able to
exploit all the current as well as charge all the capacitors CP1,
CP2, CP3, and CP4.
As a result, we improved the efficient modules of our proposed
circuit to convert the input energy of RF signals to DC voltages
and amplify it to TG voltage to be suitable for long distances.
However, we used this circuit with multi-stage circuit module
when the output voltage of the RF signals is very low in order to
double the output voltage.
The Figure 9, Figure 10 and Figure 11 show the simulation
results of the VOLDC of multi-stages at different input power
Figure 9: The Output Voltage VOLDC of passive radio-triggered wake-up
circuit at Input power PWRF of -13.85 dBm
Figure 10: The Output Voltage VOLDC of passive radio-triggered wake-up
circuit at Input power PWRF of -11.85 dBm
Figure 11: The Output Voltage VOLDC of passive radio-triggered wake-up
circuit at Input power PWRF of -9.85dBm
The Figure 12, Figure 13 and Figure 14 show the
simulation results of the VOLTG of passive radio-triggered
wake-up circuit at different distances D-rs.
Figure 12: The Output Voltage VOLTG of passive radio-triggered wake-up
circuit at 130 M
Figure 13: The Output Voltage VOLTG of passive radio-triggered wake-up
circuit at 124 M
Figure 14: The Output Voltage VOLTG of passive radio-triggered wake-up
circuit at 120 M.
In this Paper, we have presented several techniques
for enhancing the performance in WSNs over radio-
triggered wake-up capabilities by optimizing the modules of
the passive radio-triggered wake-up circuit as well as
exploring its application in the power consumption
management of WSNs. The simulation results demonstrate
that we were able to manage the radio power consumption
of WSN by harvesting energy from the RF signal and
sending a wake-up signal to the node’s MCU. We found
that this harvest takes only 15μs or less to produce wake-up
signals within the wake-up circuit and prolongs the lifetime
of the WSN nodes.
The proposed circuit receives the RF signal of the
network controller through the node antenna and produces
VOLDC by its rectifier module so that this voltage is 250
mV. This circuit can produce the VOLTG by its comparator
module which can compare the VOLDC of 10mV or more
with a threshold voltage and produce a high VOLTG which
is able to wake-up the MCU of the node. We found that the
comparator can consume less energy; only 0.3uA which is
enough to amplify VOLDC for a long distance of 100m or
more and radiation source of 2W in free-space.
Furthermore, the proposed circuit achieves synchronization
of WSNs within long distances as well as it consumes low
power consumption within these long distances.
Furthermore, the simulation results show that the proposed
circuit can produce and amplify a higher voltage with a long
distance so that it is enough to reduce the energy consumption
from 13.85% to 21.85 %.
Finally, we can say that the vast majority of the system
energy in a wireless sensor node is consumed by the radio.
Accordingly, we reduced this consumption either by
decreasing the transmission output power or by decreasing
the radio duty cycle. For future work, we plan to improve
the proposed circuit by using mechanisms that make the
nodes addressable so that only the node which is addressed
with the RF signal goes into the wake-up mode while all
other nodes stay in sleep mode.
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