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中国科技论文在线
Development of a GHz Microwave Signal Source for
Electro-Optical Switch#
Song Qiang, Huang Xiaoliang, Li Yanting, Zheng Chuantao, Wang Yiding**
(State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and 5
Engineering, Jilin University, Changchun 130012, China)
Foundations: the Ministry of Education of China (Nos. 20110061120052 and 20120061130008)
Brief author introduction:SONG Qiang (1988-), male, master candidate, mainly focuses on RF circuit design and
development
Correspondance author: ZHENG Chuan-tao (1982-), male, Associate Professor, . degree, mainly focuses on
optoelectronic device and systems.
Abstract: In this paper, a portable GHz signal source is designed and developed based on advanced
RSIC machine (ARM7) processor and lock-in amplifying technique, which includes a signal generator
and a signal amplifier. Simulation on microstrip line electrode is performed using high frequency
structure simulator (HFSS) software, and both PCB thickness and electrode width are optimized to get 10
an characteristic impedance of 50 Ω. After the integration of the overall system, measurements are
carried out to derive the performances of the signal source. Experimental results indicate that, as the
frequency increases from to GHz, the peak-to-peak amplitude range of the unamplified signal is
~333 mV, that of the amplified signal is ~ V, and the gain of the developed amplifier is
~ dB; the output power decreases from to dBm, and the cutoff frequency is 15
estimated to be about GHz under the noise level of -55 dBm. The signal source can be utilized to
supply GHz driving signals for electro-optic switches instead of the commercially avilable expensive
ones due to its compact size and acceptable performances.
Key words: Optoelectronic systems; Phase-locked loop; Frequency synthesizer; Amplifier
0 Introduction 20
With the development of electronic technologies, the speed of electric systems becomes
faster and faster, and radio-frequency (RF) signals are thus widely used in many fields [1, 2]. For
example, RF signals can be adopted as driving signals for electro-optic switches in optical
communication systems, and a standard RF signal is usually used to test the characteristic or
function of a device or a circuit, etc. Besides, it can also be used to measure the electric field 25
intensity [3, 4]. However, commercial available RF signal source is usually expensive and large in
size. Therefore, in this paper, a portable GHz signal source is designed and developed, which is
relatively small in size and easy to carry [5]. Modeling on traveling-wave electrode is established,
and simulations are done to optimize the structural parameters. ADF4350 is used as the main unit
to generate GHz sine-wave signal, and LPC2138 is utilized as the main control processor [6, 7]. 30
Since the signal generated by ADF4350 is relatively small, an RF amplifier module is also
designed and developed.
1 Theory and optimization
Characteristic impedance
The characteristic impedance Z0 of a micro-strip transmission line [8-10] is defined as the ratio of 35
input voltage ( )iU Z and input current ( )iI Z , or the negative value of the ratio of the reflected voltage
and reflected current, and it can be expressed as
0 0
0
0 0
( ) j( )
( ) ( )
i r
i r
U Z R wLU ZZ
I Z I Z G jwC
+= = − = + (1)
where R0, L0, G0 and C0 are the distributed resistance, distributed inductance, distributed conductance,
and distributed capacitance, respectively. For the lossless transmission line (R0=0, G0=0), we have 40
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中国科技论文在线
0 0 0Z L C= (2)
And also, for the microwave transmission line ( 0 0R wL<< , 0 0G wC<< ), there is
1 1
2 2
0 0 0 0 0
0
0 0 0 0 0
j 1 1R wL L R GZ
G jwC C jwL jwC
−⎡ ⎤ ⎡ ⎤+= = + +⎢ ⎥ ⎢ ⎥+ ⎣ ⎦ ⎣ ⎦
0 0 0 0
0 0 0 0
1- ( )
2
L R G Lj
C wL wC C
⎡ ⎤≈ − ≈⎢ ⎥⎣ ⎦
(3)
So under the cases of lossless transmission line or the microwave line, the characteristic
impedance of the transmission line has nothing to do with the frequency, . it is a constant. 45
S-parameters
For the general model of a two-port network, define the incident voltages as Ui1, Ui2 and reflected
voltages as Ur1, Ur2. The reflected wave can be expressed with the incident wave as [11]
1 11 1 12 2r i iU S U S U= + (4)
2 21 1 22 2r i iU S U S U= + (5) 50
Eqs. (4) and (5) can also be written as a matrix form as
11 11 12
21 222 2
ir
r i
UU S S
S SU U
⎛ ⎞⎛ ⎞ ⎛ ⎞= ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠ ⎝ ⎠
(6)
where 11 12
21 22
S S
S
S S
⎛ ⎞= ⎜ ⎟⎝ ⎠ is defined as the scattering matrix of the network, and S11, S12, S21 and S22
are named as scattering parameters. The detailed definitions of the four S-parameters are as below.
(1)
2 011 1 1
/
ir i U
S U U == , which represents the voltage reflection coefficient of port 1; 55
(2)
1 012 1 2
/
ir i U
S U U == , which represents the transmission coefficient from port 2 to port 1;
(3)
2 021 2 1
/
ir i U
S U U == , which represents the transmission coefficient from port 1 to port 2;
(4)
1 022 2 2
/
ir i U
S U U == , which represents the voltage reflection coefficient of port 2.
Thus, it is convenient to analyze the reflection and transmission characteristics of a network with
S-parameters. 60
Parameter optimization
In this section, high frequency structure simulator (HFSS) software is used to optimize the
mircostrip line electrode for realizing impedance match and avoiding signal reflection, since
mircostrip line electrode is widely used in the design of a PCB of the RF signal source.
(a)
L
G
GND
GND
SignalW
GRFin RFout
(b)
h
GG
delectric
W
GND GND
GND
signal
65
. Structure of the microstrip line electrode, (a) top view, and (b) cross-section view
Fig. 1 shows the structure of the designed microstrip line electrode, and the electrode material
is copper. The width of the signal electrode is W, and the gap between the signal electrode and
ground electrode is G. In Fig. 1(b), the dielectric layer height is h; FR-4 (epoxy glass fiber) or
rogers 4350 may be used as the dielectric materials, and the dielectric constant of FR-4 is and 70
that of rogers 4350 is . In the design, the gap G is set to be mm. Then the characteristic
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中国科技论文在线
impedance can be treated as the function of W and h.
Using HFSS platform, the effects of dielectric thickness h on characteristic impedance Z0 is
analyzed under different signal electrode width, as shown in Fig. 2(a) and Fig. 2(b), respectively,
where (a) the dielectric material is FR4, and (b) the dielectric material is rogers 4350. The effects 75
of signal electrode width W on Z0 is also analyzed under different signal dielectric height, as
shown in Fig. 3(a) and Fig. 3(b), respectively, where (a) the dielectric material is FR4, and (b) the
dielectric material is rogers 4350. It can be found that, when we take the dielectric material as FR4,
height as mm and width as mm, the characteristic impedance will be 50 Ω; when we
take the dielectric material as rogers4350, height as mm and width as mm, the 80
characteristic impedance will also be 50 Ω.
Based on the above, in the design of our PCB, the relative material and parameters are
selected as: dielectric material is FR4; G = mm; h = mm; W = mm.
20
40
60
80
Z 0
/
Ω
h /mm
W=
W=
W=
W=
W=
W=
W=(a)
20
40
60
80
Z 0
/
Ω
h /mm
W =
W =
W =
W =
W =
W =
W =(b)
85
Fig. 2. The effects of dielectric thickness h on characteristic impedance Z0 under different signal electrode width,
where (a) the dielectric material is FR4, and (b) the dielectric material is rogers 4350.
20
40
60
80
Z 0
/
Ω
W /mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
(a)
20
40
60
80
Z 0
/
Ω
W /mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
h = mm
(b)
Fig. 3. The effects of signal electrode width W on characteristic impedance Z0 under different dielectric layer 90
height, where (a) the dielectric material is FR4, and (b) the dielectric material is rogers 4350.
2 Design of hardware and software
GHz signal generator
Fig. 4(a) shows the overall block diagram of the designed RF signal source, which contains a
signal generator and a signal amplifier. For the signal generator, ADF4350 is selected as the GHz 95
signal generator, and for the signal amplifier, AD8351 is selected to amplify the generated signals.
ADF4350 (Analog Devices) contains a phase locked loop (PLL), has a supply voltage of 3~6 V,
and it can output a signal with a frequency of ~ GHz. Define a factor pdfF as
pdf ref [(1 ) / ( (1 ))]F F D R T= × + × + , where Fref is the input reference frequency, D is multiplier factor
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中国科技论文在线
of Fref, T is reference (0 or 1), and R is RF reference divider factor. Then the frequency of the 100
output signal can be decided by ( )out pdfRF F N K M= × + , where N is integer frequency factor, K
is fractional frequency factor, and M is mold. The output frequency can be determined through
setting ADF4350’s 6 registers, which is performed by the core processor LPC2138.
105
(a)
P1
SMA
P2
SMA
R1
R2
R3
R4
R10
R11
R14
R13
R15
C1
C2 C6
C5
PWUP1
RGP12
INHI3
INLO4
RGP25 COMM 6
OPLO 7
OPHI 8
VPOS 9
VOCM 10
U1
AD8351
R6
P3
SMA
P4
SMA
C3
C4
VCC
VCC
VCC
R12
(b) (c)
Fig. 4. (a) Overall block diagram of the GHz signal source, (b) amplifying circuit, and (c) photo of
the developed GHz signal source 110
GHz signal Amplifier
Since the signal generated by ADF4350 is small, we amplify it by an ultra-wideband RF/IF
amplifier AD8351. The amplifier circuit is shown in Fig. 4(b). The magnification factor of this
circuit is within the range of 0~26 dB, and the voltage gain can be approximately calculated by the
following equation 115
L 6 f L
6 L L f 6
R R R R
Gain=
R R (R R ) 39 R
× × + × ×
× × + + × + (7)
where Rf is 350 Ω (internal resistor), RL is the load impedance, and R6 is the gain setting resistor,
as shown in Fig. 4(b).
Software
First, we initialize all the related IO ports and display module, and then initialize ADF4350 to 120
set the initial frequency. Then we wait for the key being pressed. If a key is pressed, the frequency
will be modified according to the step, the registers of ADF4350 will be updated and the LCD will
be refreshed to display the new frequency.
After the integration on the hardware and software, the photo of the final developed GHz
signal source is shown in Fig. 4(c). 125
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中国科技论文在线
3 Experiment and result
Impedance measurement
The characteristic impedance of the microstrip line electrode (especially made on the PCB for
the measurement of the impedance of the electrode) is measured by using a vector network
analyzer (37269C, Anritsu Company). The measurement results are shown in Fig. 5, where the 130
impedance consists of two parts, . resistance and reactance. We can observe that the resistance
fluctuates around 50 Ω, and the reactance fluctuates around 0 Ω. So it can be concluded that the
characteristic impedance of the microstrip line reaches 50 Ω, which matches the simulation result
given in Fig. 3. .
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
C
ha
ra
ct
er
is
tic
im
pe
da
nc
e
Frequency /GHz
resistance
reactance
135
Fig. 5. Measurement results on the characteristic impedance of the mixrostrip line electrode
Signal measurement
Under the frequency of GHz, Fig. 6(a) shows the original signal without being amplified,
whose peak-to-peak value is 92 mV. And after being amplified, the amplitude reaches 1 V, as
shown in Fig. 6(b). The gain of the amplifier is about 21 dB at this frequency. 140
(a) (b)
Fig. 6. (a) signal of before being amplified, and (b) signal of after being amplified
As the frequency increases from GHz to GHz, the output amplitude of the 145
unamplified signal and that of the amplified signal are compared and shown in Fig 7(a). We can
find that the peak-to-peak amplitude of the signal decreases as the frequency increases, and the
ranges under the two cases are ~333 mV and ~ V, respectively. Under different
frequencies, the gain of the amplifier is shown in Fig. 7(b), which is determined to be within the
range of ~ dB. 150
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中国科技论文在线
(a)
100 200 300 400 500 600 700 800 900 1000
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Pe
ak
-to
-P
ea
k
V
al
ue
/m
V
Frequency /MHz
before being amplified
after being amplified
V
V
(b)
100 200 300 400 500 600 700 800 900 1000
10
15
20
25
30
G
ai
n
of
th
e
Am
pl
ifi
er
/d
B
Frequency /MHz
dB
dB
Fig. 7. (a) The output amplitude of the unamplified signal and that of the amplified signal, and (b) the gain of the
amplifier under different frequencies
Spectrum measurement 155
In order to obtain the range of the output frequency and the range of the output signal power,
a spectrum analyzer (Agilent E4401B) is used to test the spectrum of the GHz signal source under
different frequencies. Note that, since the maximum frequency of Agilent E4401B is only GHz,
the measurements are conducted below this frequency. Fig. 8(a) shows the measured spectrum
under the frequency of GHz. We can find that the output power is − dBm at this 160
frequency, and the noise level is about −55 dBm. Tuning the frequency gradually from to
GHz, the output powers under all frequencies are measured and shown in Fig. 8(b). We can find
that with the increase of frequency, the output power decreases from − to − dBm. The
linear fitting on the experimental results can also be found in Fig. 8(b), and under the noise level
of −55 dBm, the cutoff frequency is estimated to be about GHz. 165
(a) (b)
0 2 4 6
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
O
ut
pu
t P
ow
er
/d
B
m
Frequency/GHz
Experiment Dot
Fit Curve
GHz
noise level -55 dBm
Fig. 8. (a) The measured spectrum under the frequency of , and (b) experimental dots and linear fitting
cure of output powers of the developed GHz signal source
4 Conclusion 170
Based on ARM7 processor and lock-in amplifying technique, a portable GHz signal source is
designed and developed by integrating a GHz signal generator and a signal amplifier together.
Measurements are carried out to derive the performances of the GHz signal source. Experimental
results of the signal source indicate that, as the frequency increases from to GHz, the
amplitude range of the unamplified signal is ~333 mV, that of the amplified signal is 175
~ V, and the gain of the developed amplifier is ~ dB; the output power
decreases from − to − dBm, and the cutoff frequency of the signal is estimated to be
about GHz under the noise level of −55 dBm.
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中国科技论文在线
References 180
[1] WANG WQ. Design of the GHz signal source generator based on PE3336 [J]. Electronic Technology, 2004,
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[2] ZHAO design of loop filter of the frequency synthesizer [J]. Radio Engineering, 2006, 36(4):39-41.
[3] ZHANG H. Signal integrity research of high-speed interconnected system [D]. Thesis of PHD in southeast
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application [J]. Electronic Component & Device Applications, 2006, 8(3):103-104.
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[11] Zhang W,Duan X, Kou H, et al. High-speed configurable signal generator for access network system test [C].
2012 IEEE International Conference onSystems and Informatics (ICSAI), 2012, 2079-2083.
200
电光开关驱动用吉赫兹微波信号源的
研制
宋强，黄小亮，李艳婷，郑传涛，王一丁
（集成光电子学国家重点联合实验室吉林大学实验区，吉林大学电子科学与工程学院，长春
130012） 205
摘要：利用 ARM 处理器和锁相环技术，本文设计并制作了一种便携式 GHz 信号源，它包
括一个信号发生器和一个信号放大器。利用 HFSS软件对微带线电极做了仿真，对印刷电路
板（PCB）的厚度以及微带线的宽度做了优化以使微带电极的特征阻抗为 50 Ω。对整个系
统进行集成后，对其开展了详细的测试实验以得到 GHz 信号源的性能。实验结果显示，当
信号源频率从 GHz增加到 GHz时，未放大信号的峰峰值幅度范围为 ~333 mV，210
放大后的信号峰峰值幅度为 ~ V；制作的信号放大器的增益范围约为 ~ dB；
GHz信号的输出功率将从降至 dBm。在系统噪声水平为-55 dBm时，可以估计
出该系统最大的输出信号频率可达 GHz。由于具有较小的尺寸和可接受的性能，该信号
源可用来取代商业昂贵的信号源而为电光开关提供驱动信号。
215
关键词：光电子系统；锁相环；频率合成器；放大器
中图分类号：TN742;
