L Band Low Noise Amplifier

L Band Low Noise Amplifier
Junlin Song
School of Electronic Engineering
University of Electronic Science and Technology of China
Chengdu, China
693516274@qq.com
Haoquan Hu
School of Electronic Engineering
University of Electronic Science and Technology of China
Chengdu, China
huhq@uestc.edu.cn
Abstractlow noise amplifiers are the key components of the
receiver front end, it has been widely used in microwave
communication, radar, electronic warfare, and a variety of high-
precision microwave measurement system and its performance
directly affects the performance of entire receiving system, so it is
essential to develop excellent low noise amplifier. In this paper, it
has designed a LNA which has good performances at 2GHz. The
measurement results performs a high gain (>15dB), fine
flatness(<0.5dB), good noise characteristics(<1dB) and fine
input/output return loss (S
11
<-15dB,S
22
<-15dB)in the frequency
range of the design.
Keywords-component; LNA; ATF54143; Low noise;
I. INTRODUCTION
With the fast development of the high-speed wireless
communication, artificial satellite and ground penetrating radar
technology, imaging systems, low noise amplifiers have
become more and more important. For ensuring the
performance of the whole system, such as, the system
sensitivity, the LNA must have high gain, fine flatness, good
noise characteristics and fine input/output return loss
[3]
.
In this paper we use the Avago Technologies' ATF-54143
to design the amplifier in the ADS.
II. THEORIES OF LOW NOISE AMPLIFIER
When we design the amplifiers, we have some design
principles to obey, the first one is we want to reach the
maximum of power, the second one is we have to meet the goal
of a stable gain, the third one is get a fixed gain, the forth is get
the lowest noise. Usually we have to take look at the goals
shows at the above. For design of the low noise amplifier we
hope to get the lower noise and in the same time have a high
gain, then we must take compromises
[5]
.
The key performance indicators for low noise amplifier are
noise figure, gain, input and output VSWR, and flatness in the
band.
1.noise figure
The noise figure reflect the signal through the degree of the
deterioration of the low noise amplifier ,the smaller the better,
it is the most critical indicators of the low noise amplifier
design, the noise figure is related to the quiescent operating
point of the transistors and the resistance of the signal source.
2 Operating frequency
The band of the LNA should not to be to wide, the wider it
is the bigger the noise is.
3 Gain
The LNA should have a good gain, it can help to suppress
the noise figure of the system. But it can not be to high, to
avoid the nonlinear distortion which is produce by the mixer in
the mixer at the back of the system.
4 Gain flatness
The ups and downs of the gain in the passband
5 Stability
The basic of the amplifier to ensure the amplifier operates
normally, general requirement is absolutely stable. If you can
not satisfy the absolute stability conditions, the rational design
of matching to make the deviate from the unstable region.
6 Nonlinear characteristics
It is mainly determined by the third-order inter-modulation
intercept point and 1dB compression point.
The noise figure and gain has the greatest impact on the
overall performance. Always the single-stage circuit can not
meet the requirement you can use the multi-stage cascade.
When the relative bandwidth of the amplifier is less than
20%, it is generally considered narrow-band, wide-band
amplifier can cover a very wide bandwidth. when the amplifier
works in a high frequency, as the frequency increases, probably
6dB/octave
[2]
. The broadband amplifier requires it works in a
wide-band range the gain of it keeps stable. Therefore, it
required to use the appropriate method to compensate for the
loss of gain in a broadband amplifier. Moreover you should
consider the amplifier can be stable in the wide band. Usually
the broadband amplifier has the main circuit forms as the
following:
(1) Distributed amplifier
It can get a wide bandwidth, a low input VSWR and a high
gain, and a relative good noise figure. But this form of circuit
have so many devices, it costs a lot, and it is difficult to debug,
so it is not suitable for general applications.
(2) Loss match amplifier
978-1-4673-1697-2/12/$31.002012 IEEE ICCP2012 Proceedings
It has a wide bandwidth and well VSWR, however the

noise figure is bad, the output range is narrow, and it is hard
to achieve.
(3) Balanced amplifier
The biggest advantage of the balanced amplifier is it
can both obtain the minimum noise figure and good input
matching characteristics, as well as greater reliability and
greater improvements in a wide bandwidth, however, a
wide band coupler is relatively difficult.
(4) Negative feedback amplifier
Put negative feedback between FET drain and gate or
source to lower the low frequency gain, make the input
matching better, the principle of this structure is easy and
have a relative wide bandwidth, well linearity, work stably,
and the VSWR in band is well.
III. DESIGN OF LNA
The RF section of the LNA includes: appropriate transistor,
input matching network and output matching network. The
block diagram of LNA is shown as below:
Input
matching
network
transistor
Output
matching
network
Fig. 1 The block of LNA
Choosing an appropriate is important, in this paper it use
FET ATF54143.
The noise figure is defined as the ratio of input SNR and
output SNR
[1]
.
In the formula, NF is noise figure; S
in
is the input power
and N
in
is input noise figure; S
out
is output power and N
out
is
output noise figure.
in in
out out
S N
NF
S N
(3.1)
For single-stage amplifier, the noise figure is
min 2
2
4
(1 ) 1
s sopt
n
s sopt
F F R
* *

* *
(3.2)
In the formula, F
min
is the minimum noise figure of the
transistor, it is determined by the transistor only,
sopt
is the
best reflection coefficient,
s
is the reflection coefficient of
source and R
n
is the noise resistance of transistor, in the multi-
stage circuit the noise figure is determined by the formula
shown in the below :
3 2
1
1 1 2
1 1 F F
F F
G GG

(3.3)
In the formula F is the total noise figure, F
1
, F
2
, F
3
are
noise figures of the first stage, second stage and third stage
amplifiers, G
1
, G
2
are gain of the first stage and second stage
of amplifiers, from the formula we can know the total noise
figure of the circuit is determined by the first stage. So in the
designing the first stage should design should let the circuit
have best noise figure.
When the reflection coefficients of the input and output are
all less than one (|
1
|<1, |
2
|<1), regardless of the source
impedance and load impedance, the network is absolutely
stable; when input or output reflection coefficients are greater
than one, the network is not stable, it is called conditional
stability.
To the conditional stable amplifier the impedance of the
source and load could not choose freely, or the amplifier could
not work stable.
To make the amplifier stable the S parameters in the input
should fit the principle as follows
[2]
:
2
11 12 21
1 0 S S S ! (3.4)
2 2
11 22 11 22 12 21
12 21
1
0
2
S S S S S S
S S

! (3.5)
To make the amplifier stable the S parameters in the output
should fit the principle as follows:
2
22 12 21
1 0 S S S ! (3.6)
2 2
11 22 11 22 12 21
12 21
1
0
2
S S S S S S
S S

! (3.7)
There are some methods to make the amplifiers more stable,
the common methods are: (1) negative feedback, (2) Steady
decay. The ATF54143 is not absolutely stable, so it should do
something to make the transistor stable. In the paper we use
series negative feedback in the source stage.
Matching network make the source and load match with
transistor:
*
1 s
* * ,
*
2 l
* * (3.8)
But if you want get the minimum of noise figure, you could
not get the maximum output power. In the designing of LNA,
we want to get the minimum of the noise figure, so in the input
port we follow the principle of minimum noise figure, and in
the output port we follow the principle of conjugate match.
IV. SIMULATION OF LNA
The amplifier we design in the paper works at 2GHz, so we
choose the ATF54143, at the frequency of 2GHz, it can get the
gain of 18.5dB and the noise figure is 0.8dB. The DC bias is
V
ds
=3V, I
gs
=20mA. The dielectric substrate is AD1000,
r
=10,
h=0.635mm, tanD=0.003.
After making the transistors work stable, we make the input
and output network, then we get the simulation model is shown
in the figure.2:
Fig.2 simulation model

The simulation results are shown in the figures at below.
The fig.3 shows the noise figure and stable fact. In fig.4 it
shows the gain.
Fig.3 The noise figure and StabFact
Fig.4 Gain of the LNA
From the simulation results we can get the conclusions that the
circuit is absolutely stable, and the noise figure is less than 1dB, the
LNA achieves the goals we make.
V. THE MEASUREMENT
In the figure.5 it shows the sample we make, from figure.6
to figure 8, they show all the index of the LNA. All the results
are measured by signal analyzer FSV make by R&S.

Fig.5 The sample of LNA
The VSWR are measured by vector network analyzer HP8756A,
Fig.6 is the input VSWR and Fig.7 is the output VSWR.
Fig.6 Input VSWR
Fig.7 Output VSWR
The noise and gain is measured by FSV made by R&S,
Fig.8 is the gain and noise figure.
Fig.8 Gain and noise figure

VI. CONCLUSION
Measurements and simulation results are fit well, we can
conclude that all the theories in the above is right, but the input
and output VSWR is a little big, the SMA connector results a
little, and transistors are different one by one. But in all the
measurements are acceptable. The LNA in the paper is better
than others at gain and flatness and NF. It was used in the
receive system, the lower the noise figure is, the better the
system performs, so sometime we satisfy the gain to get low
noise.
REFERENCES
[1] Kuo-Hua Cheng, A novel 2.4GHz LNA with Digital Gain control using
0.18um CMOS, IEEE,2005.
[2] Dale D. Henkes, LNA design uses series feedback to achieve
simultaneous low input VSWR and low noise Applied
Microwave&WirelessOctober 1998 pp.26-32..
[3] Andrei Grebennikov, RF and Microwave Power AmplifierDesign,
McGraw-Hill,New York,2005,pp.315-339
[4] David M. Pozar, Microwave Engineering, Third Editon, John Wiley Inc.
New York, 1998, pp .612-617brev., in press.
[5] Bal S. Virdee, Avtar S. Virdee,Ben Y. Banyamin, Broadband
Microwave amplifiers,Artech House,Boston,2004,pp.8-10

L Band Low Noise Amplifier

Uploaded by

Copyright:

Available Formats

L Band Low Noise Amplifier

Uploaded by

Document Information

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

L Band Low Noise Amplifier

Uploaded by

Copyright:

Available Formats

L Band Low Noise Amplifier

It has a wide bandwidth and well VSWR, however the

Fig.2 simulation model

Fig.8 Gain and noise figure

You might also like