The Cascode LNA with RF Amplifier at 5.8GHz Using T-Matching Network for WiMAX Applications.
The Cascode LNA with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
The CasCODe LNa wITh RF ampLIFIeR aT 5.8Ghz UsING
T-maTChING NeTwORk FOR wImaX appLICaTIONs
Abu Bakar Ibrahim, Abdul Rani Othman, Mohd Nor Husain, Mohammad
Syahrir Johal, J. Sam Hamidon
Faculty of Electronic and Computer Engineering,
Universiti Teknikal Malaysia Melaka, Malaysia
Email: abupsp@gmail.com
Abstract
This paper presents the Cascode LNA with RF
ampliier at 5.8GHz using T-matching network
applicable for WIMAX application. The Cascode
LNA uses FHX76LP Low Noise SuperHEMT
FET and RF ampliier use EPA018A. The LNA
designed used T-matching network consisting
of lump element reactive element at the input
and the output terminal. The Cascode LNA
with RF ampliier produced gain of 36.4 dB and
noise igure (NF) at 1.3dB. The input relection
(S11) and output return loss (S22) are -12.4dB
and -12.3 dB respectively. The bandwidth of
the ampliier is more than 1.2GHz. The input
sensitivity is compliant with the IEEE 802.16
standards.
Keywords: Cascode LNA, RFA, T -Matching
Network.
I.
INTRODUCTION
The increasing number of personal
wireless
communication
systems
demand for Radio Frequency (RF)
front-end capable to handle diference
standard speciication, i.e. WiMAX.[1].
WiMAX, which is short for Worldwide
Interoperability for Microwave Access,
is a novel wireless communication
technology. It is an atractive technology
due to the high transmiting speed (up to
70Mbps) and long transmiting distance
(up to 30 mile). The system bases on IEEE
802.16 standards and uses several bands
(2.3-2.7 GHz, 3.4-3.6 GHz and 5.1-5.8GHz)
to transmit data. The design of the frontend low noise ampliier (LNA) is one of
the challenges in radio frequency (RF)
receivers, which needs to provide good
input impedance match, enough power
ISSN: 2180 - 1843
Vol. 4
gain and low noise igure (NF) within
the required band [2].Many high gain
ampliier topologies have been proposed
as a way to satisfy the requirement for
low power dissipation as well as good
performances. The Cascode with RF
ampliier to produces results in a higher
bandwidth and gain, due to the increase
in the output impedance, as well as beter
isolation between the input and output
ports [3]. Most of the single stage LNA
device in the review could only around
20 dB gain. It was proposed that the low
noise ampliier should have a gain of at
least 30 dB [8]. By taking consideration
the extension of communication distance
of up to 50 km [8]. A budgeted high gain
of LNA will ensure a good signal to noise
separation for further ampliication. For
this gain of 30 dB, a Cascode LNA with
RF ampliier is introduced. It is shows in
Figure 1.
Figure
Cascode
LNA
and RFA
Figure 1:1:Cascode
LNA
and RFA
II. TheOReTICaL aspeCTs
Basically, designing an ampliier, the
input and output matching network are
consider to achieve the required stability,
small signal gain, and bandwidth. Super
high frequency ampliier is a typical active
circuit used to amplify the amplitude of RF
signal. Basic concept and consideration in
design of super high frequency ampliier
No. 1
January - June 2012
15
Journal of Telecommunication, Electronic and Computer Engineering
is presented in this paper. The LNA
designed, the formula and equation were
referred to [4]. Figure 2, shows a typical
single-stage ampliier including input/
output matching networks.
for
novel
attractive
bps)
m
.3. The
of
eds
GP =
=
The basic concept of high frequency
ampliier design is to match input/output
of a transistor at high frequencies using
S-parameters frequency characteristics
at a speciic DC-bias point with source
impedance and load impedance. Input/
output matching circuit is essential
to reduce the unwanted relection of
signal and to improve eiciency of the
transmission from source to load [4],[5].
a. power Gain
Several power gains were deined in
order to understand operation of super
high frequency ampliier, as shown in
Figure 3, power gains of 2-port circuit
network with power impedance or
load impedance at power ampliier
represented with scatering coeicient
are classiied into Operating Power Gain,
Transducer Power Gain and Available
Power Gain [4],[5].
FigureFigure
3: I/O
circuit
of2-port
2-port
network
3: I/O
circuit of
network
Operating power Gain
Operating power gain is the ratio of
power (PL) delivered to the load (ZL) to
power (Pin) supplied to 2-port network.
Power delivered to the load is the
diference between the power relected
at the output port and the input power,
= power supplied to 2-port network is
and
=
16
=
− Γ
Γ
− Γ
−
Γ
ISSN: 2180 - 1843
Γ
=
Power delivered to the load
power supplied to the amplifier
1− | ΓL |2
PL
1
=
| S 21 |2
Pin 1− | Γin |2
| 1 − S 22 ΓL |2
=
=
(1)
Where, Γ indicates reflection coefficient of l
Γ coeicient
Where, Γin indicates relection
=
Figure 2: Typical ampliier design
B.
=
the diference between the input power
at the input port and the relected power.
Therefore, Operating Power Gain is
represented by
Vol. 4
of load at the input port of 2-port network
and Γs is relection coeicient
of power
− Γ
=
= to the input port.
supplied
− Γ
−
Γ
=
=
Γ
Transducer
power Gain
C.
− Γ
=
Γ
Transducer
Power Gain is the ratio of Pavs,
=
=
− Γpower available
−
Γ
maximum
Γ from source
Γ
to PL power
delivered to the load. As
Γ
maximum power is obtained
Γ when input
=
impedance of circuit network is equal
to conjugate complex
number
of power
− Γ
− Γ
=
=
impedance,
if Γin− = ΓΓs,− transducer
power
− Γ
ΓΓ
Γ
Γ
gain is Γ
represented by
Γ
Γ
Γ
represented by
GT =
Γ
Power delivered to the load
Power Available from the source
2
Γ 2
| S 21 |2 (1− | ΓΓ
P
S | )(1− | ΓL | )
= L =
Pavs | (1 − S11ΓS )(1 − S 22ΓL ) − (S12 S 21ΓS ΓL ) |2
=
= ΓL indicates load reflection
coefficie
Where,
Where,
ΓL
Γ
=
=
coeicient.
−
=
Γ
− Γ
indicates
−
Γ −
− Γ
load
ΓΓ
Γ
(2)
Γ
relection
− Γ
= GA is the ratio of
Available
=
= Power Gain,
− Γ
− Γ
Pavs , power available from
the source,
Γ
to Pavn , power available from 2-port
network, that is,. Power gain is Pavn when
=
Γin == Γs. Therefore Available
Power Gain
is given by:
=
GA =
=
− Γ
− Γ
− Γ
Power available from the amplifier
=
(3)
That is, the above formula indicates
power gain when input and output are
matched [5].
=
No. 1
Γ −Γ
− Γ
=
−
+Γ
January - June 2012
Γ
=
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ =
Γ =
Power available from the source
1− | ΓS |2
Pavn
1
| S21 |2
=
2
| 1 − S22ΓL |2
=Pavs+ | 1 −−S11ΓS |
Γ
=
Γ =
Γ
D. available
power Gain
Γ
=
ΓΓ
−− ΓΓ
− Γ
− Γ with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
The Cascode
LNA
Γ
Γ
− Γ −
ΓΓ
Γ
=Γ =
+
− Γ
=
= = =
=
=
−
Γ
−e. Γ
− Γ
Γ
Γ
Γ
Γ
− Γ
Noise
− ΓFigure
−
ΓΓ
Γ Signals and noises applied to the input
Γ
Γ=
=
ered=to
ower
ower
power
input
port of ampliier were ampliied by the
gain of the ampliier and noise of ampliier
Γ
itself is added
= to the output. Therefore,
SNR (Signal to Noise Ratio) of the output
port is smaller
than that of the input port.
Γ
=
The ratio of SNR of input port to that of
output port is referred to as noise igure
and is larger than 1 dB. Typically, noise
− Γ
= igure of 2-port transistor has a minimum
− Γat the speciied
− Γ admitance given by
value
formula:
− Γ
=
−
Γ
R
F=Fmin+ N |Ys −Yopt|2
GS
−
Γ
= low
+ noise
− transi
For
For low noise transistors, manufactures
Fmin , R N , Yopt
by
usually
provide
frequencies. N deined by formula for
Γ −Γ
−
desired
noise= igure:
+Γ
=
− Γ
(1)
F.
++
coeicient should match with Γopt and
load relection coeicient should match
*
with Γout
Γ
Γs = Γopt
Γ =ΓΓ
*
ΓL = Γout
Γ
Γ
⎛
S S Γ
= ⎜⎜ S +
− Γ
⎝
⎛
S12 S 21Γs
= ⎜⎜ S 22 +
1 − S11Γs
⎝
⎞
⎟⎟
⎠
⎞
⎟⎟
⎠
(8)
(9)
(3)
(4)
=| Γs +
− Γopt |2− F − Fmin
N=
=
| 1 + Γopt | 2
2
= 1−+| ΓS | − 4RN / Z0
= =ΓΓ ==
III. CasCODe LNa aND RFa
DesIGN
Cascode LNA is designed based on
the S-parameters were obtained from
calculation and simulation using ADS
2008. The S-parameter for Cascode LNA
is shows in Table 1.
Table 1 : S-Parameters of Cascode LNA
(5)
Frequency/dB
5.8GHz
Angle
S11
0.712
-86.54
S12
0.065
33.878
S21
8.994
178.66
S22
0.237
-10.456
Γ
Condition for matching
The overall performance of the low noise amplifier is
The scatering coeicients of transistor
−Γ
were Γdetermined.
− The only lexibility
=
+Γ
=
permited
to
the
designer is the input/
−
Γ
Γ −Γ
−
=
+
Γ
=
output matching circuit. The
input circuit
− Γ
should match to the source
and the output
Γ
Γcircuit
= Γ should
=
+match to the load in order
−
Γ
to deliver maximum power to the load.
ΓΓ device is demand,
Ater stability of active
ΓΓ ==ΓΓ == ++ −
input/output matching
− Γ
Γ circuits should
be designed so that relection
coeicient
Γ
Γ
= Γ port
= is +correlated with conjugate
of each
− Γ
complex number as given below [6]:
The overall performance of the low noise
ampliier is determined
byΓ calculating the
Γ
Γ
transducer gain GT,Γnoise igure F and the input
and output standing wave ratios, VSWRIN and
VSWROUT. The optimum, Γopt and ΓL were
obtained as Γopt = 17.949 + j48.881 and ΓL =
Γ LNA. Γ
79.913-j7.304 for single
Γ
correlated with conjugate complex
ber of
gain is
ΓIN = ΓS * = S11 +
Γ
Γ
(2)
Γ
Γ
=
+
S12 S 21 ΓL
1 − S 22 Γ
ΓL
Γ = Γ * = S + S−12 S 21ΓΓS
Γ
S − S ΓΓ
ΓOUT = ΓL * = S 22 + 12 21 S
Γ ΓΓ
1 − S11 ΓS
Γ
Γ
=Γ
Γ
(6)
(7)
⎛
Γ ⎞ stage of the
The=ΓΓ
noise= ⎜igure
⎟
ΓΓ
+ of the irst
⎜
− noise
Γ ⎟⎠ igure of the
receiver overrules
⎝
⎛
⎞
whole system.
To get Γminimum
noise
⎟⎟
Γ = Γ = Γ⎜⎜
+
igure using
transistor,
power
relection
−
Γ
⎝
⎠
Γ
Γ
Γ
Γ
Γ
Γ
Γ
ISSN: 2180 - 1843
Vol. 4
Figure 4: The Schematic Circuit for Cascode LNA
Figure 4:
The Schematic Circuit for Cascode
LNA
Figure 4 shows, the complete schematic
circuit of 5.8 GHz a cascode Low noise
ampliier. It is called inductive source
degeneration. The passive elements in
the input matching network are L1, L2
No. 1
January - June 2012
17
Γ
Γ
Γ
Γ
Journal of Telecommunication, Electronic and Computer Engineering
Γ
Γ
Π
Γ
Γ
Γ
and CΓ1.While; the passive elements in
the output matching network are L3, L4
and C2. The load transistor consist of an
inductor LD, it call peaking structure to
enhance gain and bandwidth [9]. This
transistor also improves the reverse
isolation and lowers miller efect [10],[13].
Γ
Γ
Γ
Γ
GHz
loss of overall systems. The Cascode LNA
and RF ampliier Matching component
are shown in Table 3.
Γ
Γ
Γ
Γ 3: Cascode LNA and RFA Matching
Table
parameters
Π
Components LNA(Values) RFA(Values)
L1
6.14 nH
7.21nH
L2
2.4 nH
2.65nH
L3
1.55 nH
0.67nH
L4
1.62 nH
0.75nH
C1
0.315 pF
0.3pF
C2
429.9fF
Figure 5: The Schematic Circuit for RFA
Figure 5:
The Schematic Circuit for RFA
Figure 5 shows the completed schematic
circuit of a RF ampliier with associated
component and the 3 dB atenuator
resistors. The RF ampliier was design
based on [6] and [7]. Using theoretical
design equation for the RFA, the equations
are computed using Mathcad. The FET
chosen for the design is EPA018A.The
S-parameter given for the FET is shown in
Table 2. These parameter were measured
at VDD =2V and IDS= 10mA which sets the
biasing for FET. This transistor biasing
circuit is similar with the LNA ampliier
Table 2 : S-Parameters of RF Ampliier
Frequency/dB
5.8 GHz
Angle
re
8.
S11
0.728
-103.02
S12
0.049
25.88
S21
6.327
89.98
IV. sImULaTION ResULT
Table 4 is shows the S-parameters output
for Cascode LNA, RF ampliier and
Cascode LNA with RFM. It is simulated
using Advanced Design System (ADS).
The simulation recorded that the ampliier
gain S21 is 36.1 dB. The input insertion
loss S11 is -12.14dB, overall noise igure
(NF) is 1.2dB and the output insertion loss
S22 is -10.87 dB. The relection loss S12 is
-45.47dB. These values were within the
design speciication and were accepted.
The outputs S-parameter are shown in
igure 6a, 6b and 6c.
S22
0.237
10.456
Gain, noise figure, input and output matching component
Γ
Gain, noise igure, input and output
matching component were calculated and
simulated using MathCAD and ADS 2008.
Γ
Γ
Γ
Both Γcalculated and simulated results
were almost similar shows in Table 4.
The calculated transducerΠ power gain Ώfor
matched condition was 17.3 dB. The input
matching for optimum Γopt and ΓL were
obtained as Γopt= 12.662 +j 38.168 and ΓL=
79.97- j7.286. The noise igure calculated
is 2.475 dB. The RF ampliier can also
act as an isolator for the overall frontend system and a suitable Π-network
with 50 Ώ load impedance was inserted
at the input and output of the ampliier
to provide 3 dB atenuation each for the
network. The purpose of 3 dB atenuation
is to isolate the system from the relected
load power and to improve the return
18
ISSN: 2180 - 1843
Vol. 4
Ώ
6a: S-parameters for Cascode
FigureFigure
6a: S-parameters
for Cascode
Figure
S-parameters for for
RFARFA
Figure
6b:6b:S-parameters
No. 1
January - June 2012
Ώ
The Cascode LNA with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
and the frequency response of LNA is
shown in Figure 7. The 3dB bandwidth
obtained was 1.4 GHz compliant with
targeted result of more than 1 GHz.
Table 6: S-Parameters for RF Ampliier
Figure Figure
6c: S-parameters
Cascode
6c: S-parameters for
for Cascode
withwith
RFA RFA
4: Comparison of
LNALNA
TableTable
4: Comparison
ofoutput
output
S-Parameters
(dB)
Cascode LNA
RF Amplifier
Cascode and
RFA
S11
S12
S21
S22
NF
-18.9
-22.1
19.5
-20.0
1.2
-12.5
-21.5
17.3
-12.6
2.47
-24.3
-62.6
36.1
-23.86
1.20
S Parameters
Input Reflection S11 dB
Return Loss S12 dB
Forward transfer S21 dB
Output ReflectionS22 dB
NF dB *
BW MHz
Targeted
The CasCODe LNa wITh RF ampLIFIeR aT 5.8Ghz UsING
T-maTChING NeTwORk FOR wImaX appLICaTIONs
Abu Bakar Ibrahim, Abdul Rani Othman, Mohd Nor Husain, Mohammad
Syahrir Johal, J. Sam Hamidon
Faculty of Electronic and Computer Engineering,
Universiti Teknikal Malaysia Melaka, Malaysia
Email: abupsp@gmail.com
Abstract
This paper presents the Cascode LNA with RF
ampliier at 5.8GHz using T-matching network
applicable for WIMAX application. The Cascode
LNA uses FHX76LP Low Noise SuperHEMT
FET and RF ampliier use EPA018A. The LNA
designed used T-matching network consisting
of lump element reactive element at the input
and the output terminal. The Cascode LNA
with RF ampliier produced gain of 36.4 dB and
noise igure (NF) at 1.3dB. The input relection
(S11) and output return loss (S22) are -12.4dB
and -12.3 dB respectively. The bandwidth of
the ampliier is more than 1.2GHz. The input
sensitivity is compliant with the IEEE 802.16
standards.
Keywords: Cascode LNA, RFA, T -Matching
Network.
I.
INTRODUCTION
The increasing number of personal
wireless
communication
systems
demand for Radio Frequency (RF)
front-end capable to handle diference
standard speciication, i.e. WiMAX.[1].
WiMAX, which is short for Worldwide
Interoperability for Microwave Access,
is a novel wireless communication
technology. It is an atractive technology
due to the high transmiting speed (up to
70Mbps) and long transmiting distance
(up to 30 mile). The system bases on IEEE
802.16 standards and uses several bands
(2.3-2.7 GHz, 3.4-3.6 GHz and 5.1-5.8GHz)
to transmit data. The design of the frontend low noise ampliier (LNA) is one of
the challenges in radio frequency (RF)
receivers, which needs to provide good
input impedance match, enough power
ISSN: 2180 - 1843
Vol. 4
gain and low noise igure (NF) within
the required band [2].Many high gain
ampliier topologies have been proposed
as a way to satisfy the requirement for
low power dissipation as well as good
performances. The Cascode with RF
ampliier to produces results in a higher
bandwidth and gain, due to the increase
in the output impedance, as well as beter
isolation between the input and output
ports [3]. Most of the single stage LNA
device in the review could only around
20 dB gain. It was proposed that the low
noise ampliier should have a gain of at
least 30 dB [8]. By taking consideration
the extension of communication distance
of up to 50 km [8]. A budgeted high gain
of LNA will ensure a good signal to noise
separation for further ampliication. For
this gain of 30 dB, a Cascode LNA with
RF ampliier is introduced. It is shows in
Figure 1.
Figure
Cascode
LNA
and RFA
Figure 1:1:Cascode
LNA
and RFA
II. TheOReTICaL aspeCTs
Basically, designing an ampliier, the
input and output matching network are
consider to achieve the required stability,
small signal gain, and bandwidth. Super
high frequency ampliier is a typical active
circuit used to amplify the amplitude of RF
signal. Basic concept and consideration in
design of super high frequency ampliier
No. 1
January - June 2012
15
Journal of Telecommunication, Electronic and Computer Engineering
is presented in this paper. The LNA
designed, the formula and equation were
referred to [4]. Figure 2, shows a typical
single-stage ampliier including input/
output matching networks.
for
novel
attractive
bps)
m
.3. The
of
eds
GP =
=
The basic concept of high frequency
ampliier design is to match input/output
of a transistor at high frequencies using
S-parameters frequency characteristics
at a speciic DC-bias point with source
impedance and load impedance. Input/
output matching circuit is essential
to reduce the unwanted relection of
signal and to improve eiciency of the
transmission from source to load [4],[5].
a. power Gain
Several power gains were deined in
order to understand operation of super
high frequency ampliier, as shown in
Figure 3, power gains of 2-port circuit
network with power impedance or
load impedance at power ampliier
represented with scatering coeicient
are classiied into Operating Power Gain,
Transducer Power Gain and Available
Power Gain [4],[5].
FigureFigure
3: I/O
circuit
of2-port
2-port
network
3: I/O
circuit of
network
Operating power Gain
Operating power gain is the ratio of
power (PL) delivered to the load (ZL) to
power (Pin) supplied to 2-port network.
Power delivered to the load is the
diference between the power relected
at the output port and the input power,
= power supplied to 2-port network is
and
=
16
=
− Γ
Γ
− Γ
−
Γ
ISSN: 2180 - 1843
Γ
=
Power delivered to the load
power supplied to the amplifier
1− | ΓL |2
PL
1
=
| S 21 |2
Pin 1− | Γin |2
| 1 − S 22 ΓL |2
=
=
(1)
Where, Γ indicates reflection coefficient of l
Γ coeicient
Where, Γin indicates relection
=
Figure 2: Typical ampliier design
B.
=
the diference between the input power
at the input port and the relected power.
Therefore, Operating Power Gain is
represented by
Vol. 4
of load at the input port of 2-port network
and Γs is relection coeicient
of power
− Γ
=
= to the input port.
supplied
− Γ
−
Γ
=
=
Γ
Transducer
power Gain
C.
− Γ
=
Γ
Transducer
Power Gain is the ratio of Pavs,
=
=
− Γpower available
−
Γ
maximum
Γ from source
Γ
to PL power
delivered to the load. As
Γ
maximum power is obtained
Γ when input
=
impedance of circuit network is equal
to conjugate complex
number
of power
− Γ
− Γ
=
=
impedance,
if Γin− = ΓΓs,− transducer
power
− Γ
ΓΓ
Γ
Γ
gain is Γ
represented by
Γ
Γ
Γ
represented by
GT =
Γ
Power delivered to the load
Power Available from the source
2
Γ 2
| S 21 |2 (1− | ΓΓ
P
S | )(1− | ΓL | )
= L =
Pavs | (1 − S11ΓS )(1 − S 22ΓL ) − (S12 S 21ΓS ΓL ) |2
=
= ΓL indicates load reflection
coefficie
Where,
Where,
ΓL
Γ
=
=
coeicient.
−
=
Γ
− Γ
indicates
−
Γ −
− Γ
load
ΓΓ
Γ
(2)
Γ
relection
− Γ
= GA is the ratio of
Available
=
= Power Gain,
− Γ
− Γ
Pavs , power available from
the source,
Γ
to Pavn , power available from 2-port
network, that is,. Power gain is Pavn when
=
Γin == Γs. Therefore Available
Power Gain
is given by:
=
GA =
=
− Γ
− Γ
− Γ
Power available from the amplifier
=
(3)
That is, the above formula indicates
power gain when input and output are
matched [5].
=
No. 1
Γ −Γ
− Γ
=
−
+Γ
January - June 2012
Γ
=
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ
Γ =
Γ =
Power available from the source
1− | ΓS |2
Pavn
1
| S21 |2
=
2
| 1 − S22ΓL |2
=Pavs+ | 1 −−S11ΓS |
Γ
=
Γ =
Γ
D. available
power Gain
Γ
=
ΓΓ
−− ΓΓ
− Γ
− Γ with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
The Cascode
LNA
Γ
Γ
− Γ −
ΓΓ
Γ
=Γ =
+
− Γ
=
= = =
=
=
−
Γ
−e. Γ
− Γ
Γ
Γ
Γ
Γ
− Γ
Noise
− ΓFigure
−
ΓΓ
Γ Signals and noises applied to the input
Γ
Γ=
=
ered=to
ower
ower
power
input
port of ampliier were ampliied by the
gain of the ampliier and noise of ampliier
Γ
itself is added
= to the output. Therefore,
SNR (Signal to Noise Ratio) of the output
port is smaller
than that of the input port.
Γ
=
The ratio of SNR of input port to that of
output port is referred to as noise igure
and is larger than 1 dB. Typically, noise
− Γ
= igure of 2-port transistor has a minimum
− Γat the speciied
− Γ admitance given by
value
formula:
− Γ
=
−
Γ
R
F=Fmin+ N |Ys −Yopt|2
GS
−
Γ
= low
+ noise
− transi
For
For low noise transistors, manufactures
Fmin , R N , Yopt
by
usually
provide
frequencies. N deined by formula for
Γ −Γ
−
desired
noise= igure:
+Γ
=
− Γ
(1)
F.
++
coeicient should match with Γopt and
load relection coeicient should match
*
with Γout
Γ
Γs = Γopt
Γ =ΓΓ
*
ΓL = Γout
Γ
Γ
⎛
S S Γ
= ⎜⎜ S +
− Γ
⎝
⎛
S12 S 21Γs
= ⎜⎜ S 22 +
1 − S11Γs
⎝
⎞
⎟⎟
⎠
⎞
⎟⎟
⎠
(8)
(9)
(3)
(4)
=| Γs +
− Γopt |2− F − Fmin
N=
=
| 1 + Γopt | 2
2
= 1−+| ΓS | − 4RN / Z0
= =ΓΓ ==
III. CasCODe LNa aND RFa
DesIGN
Cascode LNA is designed based on
the S-parameters were obtained from
calculation and simulation using ADS
2008. The S-parameter for Cascode LNA
is shows in Table 1.
Table 1 : S-Parameters of Cascode LNA
(5)
Frequency/dB
5.8GHz
Angle
S11
0.712
-86.54
S12
0.065
33.878
S21
8.994
178.66
S22
0.237
-10.456
Γ
Condition for matching
The overall performance of the low noise amplifier is
The scatering coeicients of transistor
−Γ
were Γdetermined.
− The only lexibility
=
+Γ
=
permited
to
the
designer is the input/
−
Γ
Γ −Γ
−
=
+
Γ
=
output matching circuit. The
input circuit
− Γ
should match to the source
and the output
Γ
Γcircuit
= Γ should
=
+match to the load in order
−
Γ
to deliver maximum power to the load.
ΓΓ device is demand,
Ater stability of active
ΓΓ ==ΓΓ == ++ −
input/output matching
− Γ
Γ circuits should
be designed so that relection
coeicient
Γ
Γ
= Γ port
= is +correlated with conjugate
of each
− Γ
complex number as given below [6]:
The overall performance of the low noise
ampliier is determined
byΓ calculating the
Γ
Γ
transducer gain GT,Γnoise igure F and the input
and output standing wave ratios, VSWRIN and
VSWROUT. The optimum, Γopt and ΓL were
obtained as Γopt = 17.949 + j48.881 and ΓL =
Γ LNA. Γ
79.913-j7.304 for single
Γ
correlated with conjugate complex
ber of
gain is
ΓIN = ΓS * = S11 +
Γ
Γ
(2)
Γ
Γ
=
+
S12 S 21 ΓL
1 − S 22 Γ
ΓL
Γ = Γ * = S + S−12 S 21ΓΓS
Γ
S − S ΓΓ
ΓOUT = ΓL * = S 22 + 12 21 S
Γ ΓΓ
1 − S11 ΓS
Γ
Γ
=Γ
Γ
(6)
(7)
⎛
Γ ⎞ stage of the
The=ΓΓ
noise= ⎜igure
⎟
ΓΓ
+ of the irst
⎜
− noise
Γ ⎟⎠ igure of the
receiver overrules
⎝
⎛
⎞
whole system.
To get Γminimum
noise
⎟⎟
Γ = Γ = Γ⎜⎜
+
igure using
transistor,
power
relection
−
Γ
⎝
⎠
Γ
Γ
Γ
Γ
Γ
Γ
Γ
ISSN: 2180 - 1843
Vol. 4
Figure 4: The Schematic Circuit for Cascode LNA
Figure 4:
The Schematic Circuit for Cascode
LNA
Figure 4 shows, the complete schematic
circuit of 5.8 GHz a cascode Low noise
ampliier. It is called inductive source
degeneration. The passive elements in
the input matching network are L1, L2
No. 1
January - June 2012
17
Γ
Γ
Γ
Γ
Journal of Telecommunication, Electronic and Computer Engineering
Γ
Γ
Π
Γ
Γ
Γ
and CΓ1.While; the passive elements in
the output matching network are L3, L4
and C2. The load transistor consist of an
inductor LD, it call peaking structure to
enhance gain and bandwidth [9]. This
transistor also improves the reverse
isolation and lowers miller efect [10],[13].
Γ
Γ
Γ
Γ
GHz
loss of overall systems. The Cascode LNA
and RF ampliier Matching component
are shown in Table 3.
Γ
Γ
Γ
Γ 3: Cascode LNA and RFA Matching
Table
parameters
Π
Components LNA(Values) RFA(Values)
L1
6.14 nH
7.21nH
L2
2.4 nH
2.65nH
L3
1.55 nH
0.67nH
L4
1.62 nH
0.75nH
C1
0.315 pF
0.3pF
C2
429.9fF
Figure 5: The Schematic Circuit for RFA
Figure 5:
The Schematic Circuit for RFA
Figure 5 shows the completed schematic
circuit of a RF ampliier with associated
component and the 3 dB atenuator
resistors. The RF ampliier was design
based on [6] and [7]. Using theoretical
design equation for the RFA, the equations
are computed using Mathcad. The FET
chosen for the design is EPA018A.The
S-parameter given for the FET is shown in
Table 2. These parameter were measured
at VDD =2V and IDS= 10mA which sets the
biasing for FET. This transistor biasing
circuit is similar with the LNA ampliier
Table 2 : S-Parameters of RF Ampliier
Frequency/dB
5.8 GHz
Angle
re
8.
S11
0.728
-103.02
S12
0.049
25.88
S21
6.327
89.98
IV. sImULaTION ResULT
Table 4 is shows the S-parameters output
for Cascode LNA, RF ampliier and
Cascode LNA with RFM. It is simulated
using Advanced Design System (ADS).
The simulation recorded that the ampliier
gain S21 is 36.1 dB. The input insertion
loss S11 is -12.14dB, overall noise igure
(NF) is 1.2dB and the output insertion loss
S22 is -10.87 dB. The relection loss S12 is
-45.47dB. These values were within the
design speciication and were accepted.
The outputs S-parameter are shown in
igure 6a, 6b and 6c.
S22
0.237
10.456
Gain, noise figure, input and output matching component
Γ
Gain, noise igure, input and output
matching component were calculated and
simulated using MathCAD and ADS 2008.
Γ
Γ
Γ
Both Γcalculated and simulated results
were almost similar shows in Table 4.
The calculated transducerΠ power gain Ώfor
matched condition was 17.3 dB. The input
matching for optimum Γopt and ΓL were
obtained as Γopt= 12.662 +j 38.168 and ΓL=
79.97- j7.286. The noise igure calculated
is 2.475 dB. The RF ampliier can also
act as an isolator for the overall frontend system and a suitable Π-network
with 50 Ώ load impedance was inserted
at the input and output of the ampliier
to provide 3 dB atenuation each for the
network. The purpose of 3 dB atenuation
is to isolate the system from the relected
load power and to improve the return
18
ISSN: 2180 - 1843
Vol. 4
Ώ
6a: S-parameters for Cascode
FigureFigure
6a: S-parameters
for Cascode
Figure
S-parameters for for
RFARFA
Figure
6b:6b:S-parameters
No. 1
January - June 2012
Ώ
The Cascode LNA with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
and the frequency response of LNA is
shown in Figure 7. The 3dB bandwidth
obtained was 1.4 GHz compliant with
targeted result of more than 1 GHz.
Table 6: S-Parameters for RF Ampliier
Figure Figure
6c: S-parameters
Cascode
6c: S-parameters for
for Cascode
withwith
RFA RFA
4: Comparison of
LNALNA
TableTable
4: Comparison
ofoutput
output
S-Parameters
(dB)
Cascode LNA
RF Amplifier
Cascode and
RFA
S11
S12
S21
S22
NF
-18.9
-22.1
19.5
-20.0
1.2
-12.5
-21.5
17.3
-12.6
2.47
-24.3
-62.6
36.1
-23.86
1.20
S Parameters
Input Reflection S11 dB
Return Loss S12 dB
Forward transfer S21 dB
Output ReflectionS22 dB
NF dB *
BW MHz
Targeted