Rectifier Circuit Designs for RF Energy Harvesting

applications
Soumaya Almorabeti, Mounir Rifi, Hanae Terchoune

To cite this version:

Soumaya Almorabeti, Mounir Rifi, Hanae Terchoune. Rectifier Circuit Designs for RF Energy Har-
vesting applications. Colloque sur les Objets et systèmes Connectés, Ecole Supérieure de Technologie
de Casablanca (Maroc), Institut Universitaire de Technologie d’Aix-Marseille (France), Jun 2019,
CASABLANCA, Morocco. �hal-02296755�

HAL Id: hal-02296755

https://hal.archives-ouvertes.fr/hal-02296755
Submitted on 25 Sep 2019

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 Rectifier Circuit Designs for RF Energy Harvesting applications
Soumaya Al Morabeti 1, Mounir Rifi 2 , Hanae Terchoune 3
soumaya.almorabeti@gmail.com

ABSTRACT: RF energy scavenging, commonly referred to as RF energy harvesting, is the capability of collecting
ambient RF energy from antennas to supply power to electronic devices. The rectifier circuit is the key component of
wireless energy harvesting system. Therefore, the development of efficient and compact rectifier circuit has become
recently a vital research topic. This paper presents a state of the art and review of the recent designs of microstrip recti-
fier circuit used for RF energy harvesting applications at 2.45 GHz and 5.8GHz.
Keywords : RF energy harvesting system, rectenna, microstrip rectifier circuit, diode, low pass filter.

1 INTRODUCTION
Wireless power transfer and RF energy harvesting are As highlighted in fig.1, the rectifying circuit consists of
an alternative technology that can reduce the depend- a HF filter, rectifier (diode), DC filter and a load. The
ency of the most wireless devices on non-autonomous input HF filter preserve the antenna from the high order
power source. They have received great attention and harmonics generated by the diode due to its nonlinear
known a successful impact in many real life applica- characteristics, and ensures the adaptation between the
tions since the last several decades, due to their fulfill- receiving antenna and the rectifying circuit. The diode
ment of remote power to electronic and electrical de- rectifies the RF signal (AC current) and converts it into
vices involving low power consumption, located in a DC signal. The output DC filter blocks all the high
unreachable area or needing expensive maintenance order harmonic frequencies produced by the rectifier in
costs [1][2].Rectenna is the most main element in RF order to protect the load. These last one is a resistive
energy harvesting system to harvest the wireless energy element that presents the input impedance of the device
from the RF sources. The components of the rectenna to be powered.
system have traditionally been focused at 2.45 GHz. To In the recent years, the challenge in designing a rectifi-
decrease the aperture sizes without sacrificing compo- er circuit is to ensure a compromise between a high
nent efficiency, the frequency of ISM band centered at output voltage and good power conversion efficiency
5.8 GHz has been investigated [3].The general block for low input power applications .Thus, the main de-
diagram of a rectenna is depicted in fig 1.This passive sign methodology is: First, selection of an adequate
element contains a receiving antenna that collects and energy harvesting circuit topology. Next, choose of an
captures the radiated microwave energy from the appropriate diode. Then, conception of a matching
transmitting antenna, and the rectifying circuit that network (bandpass filter) and low pass filter. Finally,
converts these incoming energy into DC power. Usual- optimization and simulation of the overall circuit de-
ly, printed dipole and circular polarized microstrip sign using the EM simulation software.
patch antennas are the most used in rectenna system
[4]. This review paper is organized as follows. First, the
rectifier circuit theoretical background is introduced in
section 2. In section 3, the related works and compari-
son of reviewed designs are presented .Finally, some
propositions are suggested for our own design.

2 RECTIFIER CIRCUIT BACKGROUND

2.1 Topologies
The microwave rectifier can take several topologies
depending on the configuration of the diodes used for
fig 1 : The general block diagram of a rectenna rectification. The serial and shunt topologies are the
most used in the literature .Furthermore, in order to
improve the output DC voltage, the voltage doubler or
voltage multiplier topology can also be used[5].These
conventional rectifier circuit topologies are illustrated
in fig 2.
 istic determine the overall performance of the circuit
[1]. Zero bias Schottky diodes are usually used for high
frequency rectifiers because of their high switching
capacity , low barrier (high saturation current),low
junction capacitance and low voltage threshold than the
common PN diodes .In fact, the low threshold allows
for more efficient operation at low powers, and the low
junction capacitance increases the maximum frequency
at which the diode can operate[8]. Fig 3 shows the
equivalent electrical circuit of a Schottky diode.

fig 2 : The conventional rectenna topologies: (a) series; (b)

shunt; (c) single stage voltage doubler
In the serial topology, the single diode is placed be- fig 3 : The equivalent electrical circuit of a Schottky diode
tween the RF filter and the DC filter. In the shunt to-
pology, the diode is connected in parallel between the
With the junction capacitance in Farad, the series
filters. The diode is self-biased by the DC voltage that
resistance in Ω (This resistance is due to the inability of
it generates. The single stage voltage multiplier circuit
charges to easily move through the crystal lattice struc-
or voltage doubler topology can be seen as the combi-
ture, It models the losses by joule effect of the di-
nation of the two preceding topologies. It consists of
ode,and the junction resistance in Ω. The variable
two diodes, one mounted in serial and the other in
junction resistor models the fact that the diode is either
parallel, to produce a larger output voltage.
conducting or blocked.
In effect, the mono diode topologies are mainly prefer-
The Schottky diodes have two main classes. The first
able because of their ease of implementation, their high
class is the n-type silicon with a high- barrier and low
efficiency, their small size and their low cost. They
offer the theoretical advantage of minimizing the losses values of . The second class is the p-type silicon
in the diodes [6]. However, the output voltage levels characterized by low barrier and high . For low input
for both topologies are low. The voltage doubler to- power levels applications, the p-type Schottky diode is
pology provides a high output voltage, but a low RF- recommended since it provides a higher output voltage
DC conversion efficiency compared to the mono diode compared to the n-type [10]. The most used commer-
topology. cial Schottky diodes are HSMS-285X (n-type ) and
The simulations performed in [7] prove that the voltage HSMS-286X (p-type )[9].The simulations performed in
doubler circuit is more suitable for high input power [6] shows that HSMS-285x has the largest efficiencies
levels applications (>20 dBm).The serial topology at the lowest powers. This characteristic is due to its
presents a good RF-DC conversion efficiency for low low turn-on voltage. However, it is unable to function
input power levels applications (around -10 dBm and well at larger powers because of its small reverse
20 dBm). breakdown voltage.

Each of these topologies has its advantages and limita-

tions. The choice of the suitable rectifier circuit topolo- 2.3 Energy conversion efficiency
gy is generally depends on the voltage required at the
output , the available input power and the size con- The main characteristics that should be optimized when
straint. designing rectifier circuit are the DC output voltage
and the RF-DC conversion efficiency. This last one
refers to the ratio of the PDC power recovered at the
2.2 Diode output of the rectifier and the P RF power injected at the
input of the rectifier using a microwave source. It is
determined using the formula (1) :
In designing a rectifier circuit with high RF-to-DC
conversion efficiency, the choice of a proper diode is  (%)=100. PDC (1)
one of the most important factors since the diode is the PRF
main source of loss and its performance and character- The PDC power is calculated as follows:
 2
PDC = VDC (2)
At low input power region, the efficiency is small be-
RL cause the voltage swing at the diode is below or com-
With RL is the load resistance, and VDC is the maxi-
parable with the diode turn-on threshold voltage (VT
mum DC voltage across the diode, limited by the re-
Effect). As the power continues to increase , the effi-
verse breakdown voltage Vbr by:
ciency increases and levels off with the generation of
VDC = Vbr (3) higher order harmonics. At high input power region,
2 the efficiency sharply decreases because the voltage
The PRF power is calculated using the FRIIS transmis- swing at the diode exceeds the breakdown voltage (Vbr
sion equation (4): Effect) of the diode [8]. The critical input power where
the breakdown effect becomes dominant is expressed
 
2

PRF  Pe.Ge.Gr . Vbr 2 .
 (4) as
 4.
  .r  4 RL
In addition, the RF-DC conversion efficiency strongly
It gives the received RF power as a function of the depends on the characteristics and internal parameters
transmitted power Pe, the maximum gains of the (Vbr,VT,Rs, Cj, Vj ) of the used diode, , as well as the
transmitting Ge and receiving antennas Gr and the value RL of the load. The simulations performed in
losses in the free space which depend on the frequency [6][8] prove that :
and the distance r between the two antennas .
 As the turn-on threshold voltage VT is decreased,
In fact, a variety of loss mechanisms make it difficult the energy conversion efficiency at a given power
to achieve high RF-DC conversion efficiency, especial- increases. So a low turn-on threshold is required
ly in nonlinear devices such as the diodes [8]. The for efficient and low input power applications.
maximum energy conversion efficiency of the rectifier  When the series resistance Rs increases, the energy
circuit is limited by impedance matching, device
conversion efficiency decreases. So a low value of
parasitics, and harmonic generation. It generally de-
pends on the microwave input power, the optimum Rs means that it is low losses in the diode and
connected load, the own junction voltage and break- therefore a high efficiency.
down voltage of the diode. The efficiency becomes  As the junction tension Vj is decreased, the RF-DC
quite low when the power is small or the load is not conversion efficiency increases.
matched. When the input voltage to the diode is lower  As the junction capacitance Cj, is decreased, the
than the junction voltage or is higher than the break-
RF-DC conversion efficiency increases. Cj limits
down voltage the diode does not show a rectifying
characteristic[6].Fig 4 illustrates the general relation- the maximum frequency for which a diode can op-
ship between the efficiency and losses in microwave erate.
energy conversion circuits as a function of input pow-  When the resistance of the load RL is low, the
er[1]. efficiency is high. Hence, an optimization must be
done to determine the optimum RL.

2.4 Impedance matching network

When the rectifier circuit is not properly matched to the

receiving antenna, a part of the incident power from the
antenna will be reflected back to the environment and
not absorbed. Then the available power for rectification
is automatically reduced. Thus, it is necessary to design
an impedance matching network in order to match
correctly the input impedance between the circuit and
the receiving antenna [11]. The most frequently used
matching networks are the L network, π network, and
fig 4 : General Relationship between the efficiency and losses T network .The choice of the suitable adaptation net-
in microwave energy conversion circuits as a function of work depends on the objective sought.If it is to simply
input power make a single-band adaptation, the L-network is suffi-
cient. If other functions are added to the adaptation
such as the harmonic rejection (Band-pass HF filter). T 3.1 Circuits at 2.45GHz
or π networks will be favored in this case.π type match-
The paper [19] reported a RF-DC rectifier circuit based
ing circuit attains wider bandwidth than L type match-
on modified bridge rectifier with four Schottky diodes.
ing network[7].
A maximum efficiency of 52 % and an output DC
An adaptation circuit can be composed of lumped ele-
voltage of 3.64 V have been reached over an optimal
ments such as capacitors and inductors or distributed
resistive load of 1050Ω at the input power of 10 dBm.
elements such as stubs and microstrip lines[11]. How-
The presented circuit device doesn't need neither input
ever, at high frequencies, the distributed technology is
HF filter nor bypass capacitor.
the most applied [12].In fact, at microwave frequen-
In [20], a RF-to-DC rectifier circuit has been optimized
cies, the lumped components perform poorly due to
at 2.45 GHz for an input power of 100 mW.the pro-
parasitic reactance. In order to pass from the lumped
posed circuit is based on a commercial zero bias
elements to the distributed elements, we can use the
Schottky diode HSMS-2850 ,and it is designed at the
microstrip lines and stubs in open circuit or in short
back side of the antenna in order to reduce the size of
circuit. An open circuit stub in microstrip technology is
the rectenna .The output DC voltage and overall effi-
equivalent to a parallel-mounted capacitor, and a short-
ciency are respectively higher than 1.1 V and 56% over
circuit stub is equivalent to a parallel inductor [13].
a resistive load of 2500Ω .
In [21] ,the authors have developed a microwave recti-
2.5 DC filter fier circuit ,which consisted of a short-ended T-
microstip line matching network, a Schottky diode
HSMS-2820, and an output low pass filter.The circuit
The DC filter is a low-pass filter that is the most often
provided a high conversion efficiency of 65.8% and a
composed of capacitors placed in parallel with the load
DC output voltage of 7.02V at 20dBm input power for
resistance. The filtering capacitor is the part of the
an optimum load resistor of 750 Ω.
rectifier that will block the fundamental signal and the
The paper [22] proposed a microwave double voltage
harmonics downstream of the diode. The cutoff fre-
rectifier with two Schottky diodes HSMS2820.A max-
quency must be lower than that of the fundamental
imum efficiency of 71.5% and a DC voltage output of
signal. The value of the filtering capacitor is deter-
10.75 V are reached at 22dBm of input power. The
mined from the following equation:
optimal load resistance was around 810.
A RF-DC rectifying circuit based on a Schottky diode
1 HSMS2820, with a series topology,have been devel-
C= (5)
2. . fc oped in [23].It provided an important value of output
voltage of 11.23V at 20 dBm of input power .The op-
In general, the design of microstrip low pass filters timal load resistance was around 2 k.
involves two main steps. The first one is to select an
appropriate low pass prototype (lumped-element filter Table 1 shows the results comparison of the presented
design). The choice of the type of response, including rectifier circuits at 2.45 GHz. It can be noticed that the
passband ripple and the number of reactive elements rectifier circuit proposed in [23], has presented the best
(filter order), will depend on the required specifications performances with a high output voltage of 11.23V,
[24]. Chebyshev and Butterworth are the most popular with just one rectification diode. This circuit is judged
low pass prototypes in microstrip filters design. to be compact, low cost and efficient.
Chebychev filter tolerates a slight ripple in the band-
width, but has a better rejection than the Butterworth
filter. The next step is to find an appropriate microstrip
realization that approximates the lumped element filter. Table 1: Comparison between the rectifier circuit designs at
2.45GHz
The low pass filter is widely implemented with stubs
(shunt, radial) or stepped impedance lines [13]. 
Ref Topol- Schottky Input (%) Vo RL
ogy Diode power (V) (Ω)
3 RELATED WORKS
modi-
[19] fied _ 10 52 3.6 105
In the literature, many kinds of Microstrip rectifier bridge dBm 0
circuit designs at 5.8 GHz and 2.45 GHz for RF energy rectifier
harvesting system have been proposed. This section [20] _ HSMS- 100 56 1.1 250
presents a brief review of the recent designs. 2850 mW % 0
[21] _ HSMS- 20 65. 7.0 750
2820 dBm 8 2
[22] double HSMS- 22 71. 10.
 voltage 2820 dBm 5 75 810
rectifier
[23] series HSMS- 20 _ 11. 200
2820 dBm 23 0
3.2 Circuits at 5.8 GHz Table 2: Comparison between the rectifier circuit designs at
5.8GHz


The authors in [2], have developed a microstrip rectifi- Ref Topol- Schottky Input (%) Vo RL
er that combined series and shunt configurations. It ogy Diode power (V) (Ω)
constituted of an input matching circuit (low pass filter, [2] series- HSMS-
two Schottky diodes HSMS2852 and HSMS2850,and shunt 2852,HS 0 dBm 70 2.2 600
an output filter ( three fan shaped stubs).An output DC MS-2850 0
voltage of 2.2 V and a RF-to-DC conversion efficiency [5] modfied HSMS- 0 750
of more than 70% were achieved with an optimum load doubler 2862 dBm _ 2.5 0
resistance of 6 kΩ for 0 dBm microwave incident pow- voltage
er level. [1] voltage Five of 30
In [5], a RF-to-DC rectifier circuit with a modified multi- HSMS- dBm 47 12 160
doubler voltage topology was developed for low inci- plier 2820
dent power .The rectifier circuit consisted of an imped-
[15] Greinac
ance matching network (a T-junction with short end),
her HSMS- 10 74 3.3 150
two Schottky diode HSMS-2862, and three parallel
Voltage 285C dBm 4 0
capacitors of 200 pF of each one ,have used as a DC
Doubler
low pass filter and placed in parallel with the resistance
[16] _ HSMS- 18 66. 6.3 900
R. The rectifier exhibited an output DC voltage of
286C dBm 2 3
more than 2.53V, 2.1 V and 0.61 V when the input
power was around 0 dBm,-2dBm and -10 dBm with the
We can deduce that the rectifier circuit proposed in [2]
optimum load of 7.5 KΩ.
has achieved a good efficiency of 70%, but a very low
In [1], a RF-DC rectifier circuit has been proposed
output DC voltage of 2.2 V at 0 dBm .It is need to be
using microstrip lines technology, with a voltage mul-
further improved.
tiplier topology including four schottky diodes
HSMS2820 and another diode in series with the load
resistance (160Ω )in order to improve the sensitivity. 3.3 Synthesis
This diode was acted as a variable resistor due to its
current dependence in the junction resistance. The
conversion efficiency and the output voltage reached Based on the review gained in the previous sections ,it
respectively the values of 47% and 12V for an input has been found that the main challenge in designing a
power of 30 dBm. rectifier circuit is to insure a compromise between a
In [15], the authors have implemented a rectifier circuit high output voltage ,good power conversion efficiency,
with a Greinacher Voltage Doubler topology, using small size and low cost ,especially for low input power
Schottky diode HSMS- 285C.The matching circuit applications. To achieve this purpose, some sugges-
consisted of inductors and capacitors lumped together. tions may be useful:
A load of 1500 ohm was used. The proposed rectifier  If the RF energy harvesting application required a
circuit yielded a maximum output voltage of 3.34 V larger voltage, the use of voltage doubler and volt-
and a conversion efficiency of 74.38% when the input age multiplier configurations can increase enor-
power was around 10 dBm. mously the DC output voltage.
The rectifier circuit proposed in[16] ,was integrated on
 If the size constraint is paramount, the use of series
the back side of the antenna substrate in order to mini-
mize the profile of the rectenna.The Schottky diode topology is preferred.
HSMS-286c double tube was used in series to increase  Integration of rectifier circuit on the back side of
the output DC voltage. The DC pass filter consists of a the antenna substrate can minimize the profile and
100 pF choke and a section of microstrip line. A max- the size.
imum efficiency of 66.2 % and an output DC voltage  It is recommended to use schotkky diode HSMS-
of 6.33 V have been measured with a 900 Ω load at the
285x at 2.45GHz and HSMS-286x at 5.8GHz.
input power of 18 dBm.
 Optimization of the rectifier circuit using harmonic
Table 2 summarizes the performances of these present- balance analysis and ADS simulator.
ed rectifier circuit designs.
 fils",HAL Id: tel-01705139 https://hal.laas.fr/tel-01705139
Submitted on 9 Feb 2018 .
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