INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
RF CIRCUIT DESIGN
LAB 1
MATCHING &
IMPEDANCE TRANSFORMATION
NETWORK
Full name:………………………………..
Student’s ID:……………………….........
Class:……………………………………..
Date:……………………………………...
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
I. OBJECTIVES


To learn the basic of 2-elements lumped impedance matching/transformation method.
To learn the interactive feature and the “tuning” capability of the Advance Design System
(ADS) software.
II. INTRODUCTION



Matching network serves many purposes in high frequency circuits, among them are to: (1)
Enable maximum power transfer between a source and load network. Such network is
usually called impedance matching network. (2) To tune the performance of the circuit by
controlling the impedance of the source or load, for instance in low noise amplifier design the
source impedance determines the noise contribution of the amplifier. In oscillator design the
load impedance will affect the oscillation frequency.
In this experiment, impedance transformation principle will be demonstrated using the ADS
software. The convention for terms used in impedance transformation is shown in Figure1.
The impedance transformation network used is the L impedance transformation network. The
L impedance transformation approach uses two reactive components, and has two
configurations, depending upon the values of source resistance RS and load resistance RL.
The schematics and analytical expressions for the reactance and susceptance of the L network
are shown in Figure 2.
For greater flexibility, we can use graphical method employing the Smith chart, which can
cater to transformation networks with more than two elements. The complexity of the
analytical expression grows exponentially with additional component, and is not suitable
when the impedance transformation network contains more than 3 elements.
Zs
Impedance
Transformation
Network
Vs
ZL
Image impedance
ZI
Load
impedance
Figure 1 –Impedance transformation.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
jX
jB
ZI = Rin + jXin
RL
+
jXL
(a) For RL>Rin
RL
+
jXL
(b) For RL<Rin
jX
jB
ZI = Rin + jXin
Figure 2 – The two configurations for L impedance transformation network.
For RL>Rin:
X  X in  Rin ( R L  Rin ) 
B
Rin
2
XL
RL
(1)
( R L  Rin )
 Rin X L  X in R L  XR L
(2)
For RL<Rin:
X   X L  RL ( Rin  RL ) 
B
RL
2
X in
Rin
Rin  RL
Rin X L  X in RL  XRin
(3)
(4)
III. EQUIPMENT AND PARTS LIST

ADS Software
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
IV. PROCEDURES
PROCEDURE A – PRE-LAB
Q.1. If the ZI is matched to ZS at 450MHz, compute the input impedance ZI if ZS=50 at 450MHz.
Q.2. What is the input impedance ZI if ZS=(50 - j40)  at 450MHz and the ZI is matched to ZS at
450MHz,
Q.3. Design an impedance transformation network
-
What is the input impedance ZI if ZS=(35 – j20)  at 450MHz, the ZI is matched to ZS
-
The load is modeled by a 300 resistor in parallel with a 0.82 pF capacitor. At 450MHz,
the load impedance ZL can be calculated as:
R
Z L  R // j1C 
1  jRC

  2 450  10 6

Z L  202 .1852  j140 .6297
-
Since ReZ L   R L  202 .1852  ReZ s   R s  35 , configuration (a) of Figure 2.2 is
used.
Determine the value of components of L transformation network
PROCEDURE B – VERIFY THE IMPEDANCE TRANFORMATION NETWORK BY ADS
SOFTWARE
1. Log into workstation.
2. Run the ADS version 2009 software (you might use a newer version of the software).
3. From the main window of ADS, create a new project folder named “Impedance_Transform” as
shown in Figure 3.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
Figure 3 – Opening a new project in ADS.
4. The new schematic window will automatically appear once the project is properly created.
Otherwise you can manually create a new schematic window by double clicking the Create New
schematic button on the menu bar.
5. Form value of components obtained in Q.3, draw the schematic as shown in Figure 4. Save the
schematic as “schematic1.dsn”. The various components used in Figure 4 can be obtained from
the palette list of the draw schematic window as shown in Figure 4. We see from Figure 4 that
this is an S-parameter simulation, requesting the software to calculate the S-parameters as seen
from component Term1 at frequency 450 MHz.
6.
We wish to
find s11 as
seen from
Term1
Figure 4 – The schematic.
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SCHOOL OF ELECTRICAL ENGINEERING (EE)
Figure 5 – The pallete for lumped components.
7. Now run the simulation by clicking the button
.
8. The ADS software will automatically invoke a data display window. The data display window
is used to show the result of the simulation. You can also invoke the data display window
manually by clicking the button
.
9. Insert a Smith Chart in the data display window as shown in Figure 6.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
Click this button to
insert an X-Y plot
Click this button to
insert a Smith chart
Display
area
Select S(1,1) to show
the s11 as measured
from Term1 in the
Smith chart
Figure 6 – Inserting a Smith chart in the display area. Also shown are typically used buttons.
9. Your Smith Chart should look similar to the one shown in Figure 6. Use a Marker to display the
complex value of the S11. Note that both impedance and admittance coordinates are shown in the
Smith Chart.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
Marker
The value of S11
and impedance
as indicated by
the Marker
Figure 7 – The Smith chart for S11 at 450 MHz as seen from component Term1.
10. Now we also want to show the S11 of the required image impedance ZI on the Smith chart. Verify
that the S11 of ZI = 35+j20. Note that S11 = I , the reflection coefficient of the impedance. The
equations are shown as below
PROCEDURE C – USING SMITH CHART UTILITY TO BUILD A MATCHING NETWORK
Example: Design the impedance translation circuit if ZI=50, ZL=554-j*220
1. In the current schematic, click on the commands: Tools > Smith Chart (this is the same as
DesignGuide > Filter and then selecting the Smith Chart Control window).
2. Click the Palette icon shown here - this adds the Smith Chart palette with the Smith Chart icon to
your schematic.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
3. In the schematic, insert the Smith Chart Matching Network component (also known as a Smart
Component) near the input of the amplifier – no need to connect it – but it is required. Also, click
OK when a message dialog appears.
4. Go back to the Smith Chart control window and type in the Freq (GHz) to 1.9 as shown here.
5. In the lower right corner of the Smith Chart utility window, select the ZL component and type in
the impedance looking into the amplifier from the last simulation: 554- j*220 as shown here and
click Enter.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
6. Notice that the load symbol on the Smith chart has relocated as shown here. Next, select the
shunt capacitor from the palette and move the cursor on the Smith chart: when you get to the 50
Ohm circle of constant resistance, click to stop, as shown here (it does not have to be exact for
this exercise).
7. Next, select the series inductor and move the cursor along the circle until you reach the center of
the Smith chart and then click. Now you have a 50 Ohms match between the load and source.
8. To have the DesignGuide build the circuit, click the button on the bottom of the window: Build
ADS Circuit. Click OK to any messages that appear.
9. On the schematic, push into the Smith Chart component and you should see the network similar to
the one as shown here. You values may be slightly different which is OK. Pop out when finished.
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
L=14.34nH2
C=400fF
Q.4. Design transformation network if ZI=35+j20, ZL=202.185 –j*140.62 at 450MHz. Compare the
impedance translation network in Q.4 with it in Q.3.
Q.5. Design an L transformation network for the circuit Zin=50, ZL= 100-j*30. The operating
frequency is 2GHz
Fig.2.a
L=4.37nH (nt)
C=575.7fF (//)
Q.6. Design an L transformation network for the circuit Zin=50, ZL= 100-j*30. The operating
frequency is 2GHz
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
Fig.2.b
L=4.37nH (nt)
C=575.7fF (//)
Q.7. Design an L transformation network for the circuit Zin=50+j*50, ZL= 100-j*20. The operating
frequency is 2GHz
Fig.2.c
L=8.13nH (nt)
C=646fF (//)
Q.8. Design an L transformation network for the circuit Zin=50+j*50, ZL= 100-j*20. The operating
frequency is 2GHz
Fig.2.d
Q.9. Design an T transformation network for the circuit Zin=50, ZL= 20. The operating frequency is
2GHz
Q.10. Given the Fig.3, the Vs=2cos(2106t), ZS =50Ω, ZL=20Ω
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INTERNATIONAL UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING (EE)
a. Using ADS to determine the power absorbed by the load in case that matching circuit is not
added.
b. Using ADS to design a L matching circuit, and determine the power absorbed by the load in
case that the matching circuitis used.
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