ISSN: 2180 - 1843 Vol. 4 No. 1 January - June 2012 Journal of Telecommunication, Electronic and Computer Engineering
16
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
Figure 2: Typical ampliier design
The basic concept of high frequency ampliier design is to match inputoutput
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].
Γ −
Γ −
Γ −
= =
=
Figure 3: IO circuit of 2-port network
Γ Γ
Γ Γ
Γ
= Γ
Γ
Γ Γ
Γ Γ ⎟⎟⎠
⎞ ⎜⎜⎝
⎛ Γ
− Γ
+ =
Γ =
Γ
Γ Γ
− Γ
− Γ
− Γ
− Γ
− =
= =
Γ −
Γ −
Γ −
= =
=
− +
=
Γ −
Γ +
= Γ
= Γ
Γ −
Γ +
= Γ
= Γ
Γ +
− =
Γ −
Γ −
Γ =
Figure 3: IO circuit of 2-port network
B. Operating power Gain
Operating power gain is the ratio of power P
L
delivered to the load Z
L
to power P
in
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,
and power supplied to 2-port network is the diference between the input power
at the input port and the relected power. Therefore, Operating Power Gain is
represented by
2 22
2 2
21 2
| 1
| |
| 1
| |
| |
1 1
supplied
L L
in in
L P
S S
P P
amplifier the
to power
load the
to delivered
Power G
Γ −
Γ −
Γ −
= =
=
Where, Γ indicates reflection coefficient of l
Γ
Γ Γ
Γ
=
Γ Γ
Γ Γ
Γ Γ ⎟⎟⎠
⎞ ⎜⎜⎝
⎛ Γ
− Γ
+ =
Γ =
Γ
Γ Γ
− Γ
− Γ
− Γ
− Γ
− =
= =
Γ −
Γ −
Γ −
= =
=
− +
=
Γ −
Γ +
= Γ
= Γ
Γ −
Γ +
= Γ
= Γ
Γ +
− =
Γ −
Γ −
Γ =
1 Where, Γ
in
indicates relection coeicient of load at the input port of 2-port network
and Γ
s
is relection coeicient of power supplied to the input port.
C. Transducer power Gain
Transducer Power Gain is the ratio of P
avs
, maximum power available from source
to P
L
power delivered to the load. As maximum power is obtained when input
impedance of circuit network is equal to conjugate complex number of power
impedance, if Γ
in
= Γ
s
, transducer power gain is represented by
Γ −
Γ −
Γ −
= =
=
Γ Γ
Γ Γ
represented by
Where, Γ
L
indicates load reflection coefficie
=
Γ Γ
Γ Γ
Γ Γ ⎟⎟⎠
⎞ ⎜⎜⎝
⎛ Γ
− Γ
+ =
Γ =
Γ
2 21
12 22
11 2
2 2
21
| 1
1 |
| |
1 |
| 1
| |
L S
L S
L S
avs L
T
S S
S S
S P
P source
the from
Available Power
load the
to delivered
Power G
Γ Γ
− Γ
− Γ
− Γ
− Γ
− =
= =
Γ −
Γ −
Γ −
= =
=
− +
=
Γ −
Γ +
= Γ
= Γ
Γ −
Γ +
= Γ
= Γ
Γ +
− =
Γ −
Γ −
Γ =
2 Where, Γ
L
indicates load relection coeicient.
D. available power Gain
Available Power Gain, GA is the ratio of P
avs
, power available from the source, to P
avn
, power available from 2-port network, that is,. Power gain is P
avn
when Γ
in
= Γ
s
. Therefore Available Power Gain is given by:
Γ −
Γ −
Γ −
= =
=
Γ Γ
Γ Γ
Γ
=
Γ Γ
Γ Γ
Γ Γ ⎟⎟⎠
⎞ ⎜⎜⎝
⎛ Γ
− Γ
+ =
Γ =
Γ
Γ Γ
− Γ
− Γ
− Γ
− Γ
− =
= =
2 22
2 21
2 11
2
| 1
| 1
| |
| 1
| |
| 1
L S
S avs
avn A
S S
S P
P source
the from
available Power
amplifier the
from available
Power G
Γ −
Γ −
Γ −
= =
=
− +
=
Γ −
Γ +
= Γ
= Γ
Γ −
Γ +
= Γ
= Γ
Γ +
− =
Γ −
Γ −
Γ =
3 That is, the above formula indicates
power gain when input and output are matched [5].
ISSN: 2180 - 1843 Vol. 4 No. 1 January - June 2012 The Cascode LNA with RF Ampliier at 5.8GHz Using T-Matching Network for WiMAX Applications
17
e. Noise Figure
