28 GHz balanced pHEMT VCO with low phase noise and high output power performance for 5G mm-wave systems

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 10, No. 5, October 2020, pp. 4623~4630
ISSN: 2088-8708, DOI: 10.11591/ijece.v10i5.pp4623-4630  4623
Journal homepage: http://ijece.iaescore.com/index.php/IJECE
28 GHz balanced pHEMT VCO with low phase noise and high
output power performance for 5G mm-wave systems
Abdelhafid Es-saqy1
, Maryam Abata2
, Mahmoud Mehdi3
, Said Mazer4
, Mohammed Fattah5
,
Moulhime El Bekkali6
, Catherine Algani7
1,2,4,6
Artificial Intelligence, Data Sciences and Emerging Systems Laboratory, Sidi Mohamed Ben Abdellah University, Morocco
3
Microwaves Laboratory, Lebanese University, Lebanon
5
EST, My Ismail University, Morocco
7
ESYCOM (EA2552), Conservatoire National Des Arts Et Métiers, France
Article Info ABSTRACT
Article history:
Received Dec 16, 2019
Revised Mar 12, 2020
Accepted Mar 30, 2020
This paper presents the study and design of a balanced voltage controlled
oscillator VCO for 5G wireless communication systems. This circuit is
designed in monolithic microwave integrated circuit (MMIC) technology
using PH15 process from UMS foundry. The VCO ensures an adequate
tuning range by a single-ended pHEMT varactors configuration. The simulation
results show that this circuit delivers a sinusoidal signal of output power
around 9 dBm with a second harmonic rejection between 25.87 and 33.83
dB, the oscillation frequency varies between 26.46 and 28.90 GHz, the phase
noise is -113.155 and -133.167 dBc/Hz respectively at 1 MHz and 10 MHz
offset and the Figure of Merit is -181.06 dBc/Hz. The power consumed by
the VCO is 122 mW. The oscillator layout with bias and RF output pads
occupies an area of 0.515 mm2
.
Keywords:
5G
Colpitts VCO
Low phase noise
mm-wave band
pHEMT transistor Copyright © 2020Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Abdelhafid Es-saqy,
Artificial Intelligence, Data Sciences and Emerging Systems Laboratory,
Sidi Mohamed Ben Abdellah University,
Dar Said, Tissa, Taounate, Morocco.
Email: abdelhafid.essaqy@usmba.ac.ma
1. INTRODUCTION
Reflected by the fast pace of technology innovation, wireless communication is the fastest growing
technology in the world. Currently, necessitates more than ten billion of machine-to-machine communications and
Internet of Things to fulfil the requirements for autonomous vehicles, intelligent home, smart grid, smart
city [1] and E-health services [2, 3]. Therefore, the enormous need for the new broadband frequencies [4].
Fortunately, large quantities of relatively inactive spectrum exist in the millimeter wave band [5]. The most
recent researches focused on the 28 GHz band, the 38 GHz band, the 60 GHz band and the E-band [6].
The object of a communication system is to establish seamless communications with reasonable cost
and reduced power consumption, the upcoming mobile communication system generation 5G is aiming to
fulfil these important requirements [4]. Any RF transmission / reception shown in Figure 1 system has one or
more local oscillators. An oscillator is an autonomous system generating a fixed or variable frequency signal [7].
In RF transceivers, oscillator signals are used as a frequency reference to convert the RF signal to an
intermediate frequency. In all RF applications, it is necessary to have sinusoidal references of a high spectral
purity, this is, moreover, one of the most important characteristics of an oscillator.
In the literature, many VCOs have a relatively good FoM, however, observing the covered
frequency range, we notice that it is very low: 5.45% and 6.91% of the central frequency for the two VCOs
proposed in [8], 5.44% and 3.3% respectively for the VCOs proposed in [9, 10]. On the other side, structures
with wide frequency ranges but low phase noise levels, less than -102 dBc/Hz, which do not fulfill the 5G

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 10, No. 5, October 2020 : 4623 - 4630
4624
requirements [11-13]. In addition to all these considerations, there is also the problem of the large space
occupied by these circuits, of which it is in the order of 1.5 mm2
[9] or much more [12-14].
In this paper, a large tuning range MMIC VCO with good phase noise level is proved. The circuit is
designed based on a balanced Colpitts architecture. It has a tuning range that exceeds 8.8 % of central
frequency and a phase noise around -113 dBc/Hz at 1 MHz offset. This circuit is designed based on
the pseudo-morphic High Electron Mobility Transistor pHEMT of PH15 process from UMS foundry,
dedicated to RF applications, with a cut off frequency of fT = 110GHz and a 0.15 µm gate length [15].
The remainder of this paper is structured as follows: Section 2 presents the 5G mm-Wave VCO circuit
design, Section 3 reports VCO layout and discusses the simulation results. A conclusion is given in section 4.
Figure 1. Simplified diagram of transmission/reception system
2. 5G MM-WAVE VCO DESIGN
After choosing the semiconductor technology and transistor type, it is time to choose the most
suitable VCO topology for the 5G mm-wave band application. The simplified schematic (i.e., without
transmission lines) of the studied VCO is shown in Figure 2, it is a modified version of the Colpitts structure,
which combines a good phase-noise level with improved starting conditions. The active part of the VCO is
composed of the two GaAs pHEMT transistors, T1 and T2, of gate length of 4*0.15 µm and width of 20 µm,
and their bias elements, we have chosen transistors with a high number of fingers to increase the output
power [9]. The performance of the active device, at the millimeter frequency, depends strongly on biasing
conditions [16], the biasing of these transistors is provided by the two voltage sources Vds and Vgs of 2 V
and 0.2 V respectively. While the inductance Lr as well as the two varactors T3 and T4 constitute
the resonator. These varactors are based on the pHEMT transistor whose source is connected to the drain,
the capacitance value of these varactors is controlled by the voltage applied to the gate Vtune. Finally,
a capacitor C has been added at the output of the oscillator whose role is to filter the DC component which
comes from the bias sources. We announce that this circuit is based on the PH15 process elements of
the UMS foundry, whose behavior is very close to reality, thus they present parasites and imperfections.
Figure 2. pHEMT balanced VCO circuit

Int J Elec & Comp Eng ISSN: 2088-8708 
28 GHz balanced pHEMT VCO with low phase noise and… (Abdelhafid Es-saqy)
4625
3. SIMULATIONS AND DISCUSSIONS
At millimeter frequencies, parasitic capacitances, transmission line inductances and other
connections can catastrophically change reactances and can have a significant impact on the performance of
the final circuit, which is why several optimization and retro-simulation steps are performed before the final
layout as shown in Figure 3. Particular attention is paid to the Layout symmetry, to avoid the introduction of
asymmetry in the oscillation waveforms and thus introduce additional phase noise [17]. According to
the circuit layout as shown in Figure 3, we observe three bias pads, one pad for the tuning voltage Vtune and
one RF pad for the output signal. The circuit is implanted on the GaAs substrate, it is a multilayer
technology. The total number of layers used in the PH15 process is 16 layers [18]. The length of this Layout
is 0.761 mm while the width is 0.677 mm, thus a total surface area of 0.515 mm2
, since this surface includes
the VCO with RF pad, the tuning voltage pad and the three bias pads as well as the capacity that acts as a low
pass filter. We can note that it is a very compact Layout and takes up a small area compared with
the architecture published in the literature.
Figure 3. Layout of 5G mm-wave voltage controlled oscillator
After checking the start-up conditions of our oscillator using the "OscTest" tool provided by
Agilent's ADS software. A transient simulation is executed to verify the stability of the output signal.
Figure 4 shows that the start-up conditions of the oscillations are very good, the oscillations start effectively,
and they are perfectly stable.
Figure 4. Temporal variation of the output signal Vout for Vtune= 2 V

 ISSN: 2088-8708
4626
The harmonic simulation shows that the minimum value of the output power is 5.02 dBm, while
the maximum value is 9.75 dBm. The second harmonic rejection varies between 25.87 and 33.83 dB for
the oscillation frequencies 28.12 and 26.48 GHz respectively, while the third harmonic rejection varies
between 44.75 and 55.93 dB for the oscillation frequencies 28.41 and 26.48 GHz respectively shown in
Figure 5. Therefore, we notice that our circuit has a good level of rejection of unwanted harmonics.
In Figure 6 we have plotted the variation of the oscillation frequency as a function of the tuning
voltage Vtune. For a variation of the tuning voltage Vtune from -2 to 2.5 V, the oscillation frequency varies
from 28.90 to 26.46 GHz. Therefore, a tuning range of 2.44 GHz and a gain of KVCO=542 MHz/V are
achieved. Figure 7 shows the temporel variation of the output signal Vout for Vtune=2.5 V, therefore it is
a perfectly sinusoidal signal.
Figure 5. Output power of the first harmonic (-□-),
second harmonic (-Δ-) and third harmonic (-x-)
versus tuning voltage Vtune
Figure 6. Variation of the oscillation frequency versus
tuning voltage Vtune
Figure 7. Temporal variation of the output signal for Vtune=2.5 V
The VCO performance determines the characteristics of the entire transmission system, therefore, to
have a signal of high spectral purity, the VCO phase noise must be as minimal as possible [19, 20]. Figure 8
shows the single sideband phase poise and the absolute noise voltage spectrum for Vtune=1.5 V,
thus the phase noise is -93.04 and -113.155 dBc/Hz at the offset frequency of 100 KHz and 1 MHz
respectively. On the other hand, the simulation shows that the power consumed by this VCO topology is122 mW.

4627
(a) (b)
Figure 8. Single sideband phase noise, (a) absolute noise voltage spectrum, (b) for tuning voltage Vtune= 1.5 V
Depending on the desired application, a voltage-controlled oscillator could even have completely
different specifications, making it difficult to compare VCOs with each other. A FoM merit factor is then
defined to represent the overall performance of an oscillator [14, 21-23]:
FoM = 𝐿(𝑓0, 𝛥𝑓) + 10 log(𝑃𝐷𝐶) − 20 log(
𝑓0
𝛥𝑓
) (1)
where 𝐿(𝑓0, 𝛥𝑓) is the phase noise at 𝛥𝑓 frequency offset, 𝑓0 is the oscillation frequency and 𝑃𝐷𝐶 is the power
consumption of VCO in mW.
To compare the performance of our voltage controlled oscillator circuit with other structures
published in the literature; Table 1 summarizes the performance of different oscillators, designed with
different technologies, operating in the same frequency band and dedicated for the same applications.
From Table 1 we can see that the architecture proposed in this paper has very good performance; the best level of
phase noise, an excellent output power, a low power consumption and therefore a good figure of merit.
Table 1. Performance comparison of different VCOs
Ref.
Central
frequency
(GHz)
Tuning
range
(GHz)
Output
power
(dBm)
Phase noise
(dBc/Hz) at
1MHz
FoM
(dBc/Hz)
Chip
area
(mm2
)
Structure Technologie
[8] 25.6 1.77 3 -101.9 -176.7 0.034
On-chip
inductor
0.13 µm CMOS
[8] 40.7 2.22 -6.6 -94.8 -172.1 0.018
On-chip
inductor
0.13 µm CMOS
[12] 29.4 14.8 4.5 -100.7 -169.11 3.75
4 Colpitts
VCO
0.13 Um
SiGeBiCMOS
[13] 28.3 3.8 11.8 -102 - 0.5
Negativeres
istance
0.15 µm pHEMT
This
work
27.7 2.44 9.75 -113.155 -181.06 0.515 Colpitts
0.15 µm GaAs
pHEMT
Finally, in order to characterize the performance of a millimeter frequency circuit, the effect of
technological dispersion must be evaluated. The Monte Carlo analysis proposed by the ADS software,
allows to cause small random variations in the values of the different circuit parameters, and to predict
the impact of these variations on the performance of our circuit [24, 25]. We performed a Monte Carlo
analysis at 50 iterations. Figure 9 shows the results of technological dispersion. We can deduce that for all
iterations, the fundamental harmonic power and the second harmonic power are subject to limited and
acceptable variations over the entire tuning range.

 ISSN: 2088-8708
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Figure 9. Monte Carlo analysis for the output power of the first harmonic (solid line)
and the second harmonic (dash-dotted line)
4. CONCLUSION
In this paper we have presented and designed a pHEMT balanced VCO in MMIC technology for 5G
mm-wave band systems. The simulations results showed a tuning range of 2.44 GHz (which represents
8.82% of the central frequency), an output power of 9 dBm, a phase noise of -113.155 dBc/Hz at 1 MHz
offset frequency and a figure of merit of -181.06 dBc/Hz. The Layout area is 0.515 mm2
.
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BIOGRAPHIES OF AUTHORS
Abdelhafid Es-saqy, was born in TISSA, Morocco, in January 1992. Received his Master
degree in Microelectronics from faculty of sciences Dhar EL Mahraz Fez Morocco, in 2018.
He is now Ph.D. student in Artificial Intelligence, Data Sciences and Emerging Systems
Laboratory at the University of Sidi Mohamed Ben Abdellah Fez. His main research interest
includes Mixers and Local Oscillators.
Maryam Abata, born in 1989 in Nador, Morocco, obtained Master’s degree in 2012 at
the National School of Applied Sciences. She received the Ph.D. in Telecommunications and
Micro-waves devices from Sidi Mohamed Ben Abdellah University of Fez
Mahmoud Mehdi was born in Beirut, Lebanon, in 1974. He received his Ph.D. in high
frequency communication systems from the university of Paris Marne la Vallée, France 2005. He
is an associate professor in the Physics Department of the Faculty of sciences at the Lebanese
University, Beirut, Lebanon. His research interests include Monolithic Microwave Integrated
Circuits (MMIC), Micro-Electro-Mechanical Systems (MEMS), Radiofrequency, Double
Balanced and Distributed Mixers, Local Oscillator, TW Amplifiers, Optoelectronic Mixer for
LIDAR system, Optical systems and design, and Photo-detectors. He is course leader in
microwave devices for the Masters program in Electronics
Said Mazer, born in 1978. PhD in electronics and signal processing at the University of Marne-
La-Vallée. Currently professor at the National School of Applied Sciences of Fez, Morocco and
he is a member of Artificial Intelligence, Data Sciences and Emerging Systems Laboratory at
the University of Sidi Mohamed Ben Abdellah Fez.

 ISSN: 2088-8708
4630
Mohammed Fattah, received his Ph.D. in Telecommunications and CEM at the University of
Sidi Mohamed Ben Abdellah (USMBA) Fez, Morocco, 2011. He is a professor in the Electrical
Engineering Department of the High school of technology at the Moulay Ismail University
(UMI), Meknes, Morocco and he is member of the team research ‘Information Processing and
Transmission’, LIA laboratory, UMI.
Moulhime El Bekkali, received the PhD. degree in 1991 from the USTL University Lille 1,
France, he worked on X-band printed antennas and their applications to microwave radar. He is
a professor in the Electrical Engineering Department of Superior School of Technology, Fez
(ESTF). He is member of Artificial Intelligence, Data Sciences and Emerging Systems
Laboratory. Since 2009, Pr. El Bekkali served as vice President at University of Sidi Mohamed
Ben Abdellah (USMBA) Fez, Morocco.
Catherine Algani, born in 1963. PhD in electronics at the University Pierre and Marie Curie
(Paris VI). University professor at the National Conservatory of Arts and Crafts, CNAM-Paris.
She is the responsible of the research team “communication systems” at ESYCOM laboratory.

28 GHz balanced pHEMT VCO with low phase noise and high output power performance for 5G mm-wave systems

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