2.4 GHz low noise amplifier with the BFG480W

APPLICATION INFORMATION
2.4 GHz low noise amplifier
with the BFG480W
Philips Semiconductors
Application information
2.4 GHz low noise amplifier with the BFG480W
ABSTRACT
• Description of the product
The BFG480W is one of the Philips double polysilicon wideband transistors of the BFG400 series.
• Application area
Low voltage high frequency wireless applications.
• Presented application
A low noise amplifier for 2.4 GHz applications such as wireless local area network and wireless local loop.
• Main results
At a frequency of 2.4 GHz, the amplifier has an insertion power gain of approximately 9.5 dB, a noise figure of
approximately 3 dB, and a third order intercept point of approximately 17 dBm (measured at input).
 PHILIPS ELECTRONICS N.V. 1999
All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright
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The information presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its
use. Publication thereof does not convey nor imply any license under patent- or other industrial or intellectual property
rights.
1999 Dec 22
2
Philips Semiconductors
Application information
2.4 GHz low noise amplifier with the BFG480W
INTRODUCTION
With the Philips double polysilicon wideband transistor BFG480W, it is possible to design Low Noise Amplifiers (LNAs)
for high frequency applications with a low current and a low supply voltage. These amplifiers are well suited for the new
generation low voltage high frequency wireless applications. One feature of the BFG480W is that it has a good linearity
performance. Therefore the BFG480W is well suited for LNAs with high linearity demands, such as Code Division
Multiple Access (CDMA) systems. This application note gives an example of a 2.4 GHz LNA with the BFG480W.
Because this LNA design has a high third order intercept value of 17 dBm (measured at input), it can be used for Wireless
Local Area Network (WLAN) front-end and Wireless Local Loop (WLL) applications.
CIRCUIT DESCRIPTION
The following initial conditions apply for the amplifier design:
• Vsupply ≈ 3.6 V
• VCE = 2 V
• IC = 40 mA
• f = 2.4 GHz.
The circuit is designed to show the following performance:
• s212 ≈ 9 dB
• VSWRIN < 2
• VSWROUT < 2
• NF ≤ 3.5 dB
• IP3i > 15 dBm.
The output matching is realised with an LC combination. Also an extra emitter inductance (micro stripline) is used on both
emitter-leads to improve the matching and the noise figure.
CIRCUIT DIAGRAM
R2
handbook, full pagewidth
Vsupply
C3
C2
R1
input
50 Ω
C4
L1
output
50 Ω
W1
C1
TR1
µS1,
µS2:
L1
L2
µS1
µS2
MGS628
Fig.1 Circuit diagram.
1999 Dec 22
L3
D1
3
W2
Philips Semiconductors
Application information
2.4 GHz low noise amplifier with the BFG480W
COMPONENT LIST
Table 1
Component list for the 2.4 GHz LNA
COMPONENT
VALUE
TR1
BFG480W
R1
2.7
UNIT
kΩ
SIZE, MANUFACTURER
PURPOSE, COMMENT
SOT343R Philips
RF transistor
0603 Philips
collector to base bias
R2
39
Ω
0603 Philips
collector series bias; levelling hFE spread
C1
5.6
pF
0603 Philips
input match (base coupling)
C2
3.3
pF
0603 Philips
output match (collector coupling)
C3
5.6
pF
0603 Philips
2.4 GHz short (L1 to ground)
C4
1
nF
0603 Philips
RF collector bias decoupling
L1
150
nH
0805CS Coilcraft
µS1
see Table 2
emitter induction: micro stripline and via-hole
µS2
see Table 2
emitter induction: micro stripline and via-hole
PCB
FR4
εr ≈ 4.6, d = 0.5 mm
Table 2
output match
Dimensions of the micro striplines µS1 and µS2 (see Fig.1)
DIMENSION
VALUE
UNIT
DESCRIPTION
L1
1.0
mm
length micro stripline; Zo ≈ 48 Ω
L2
1.0
mm
length interconnect micro stripline and via-hole area
L3
1.0
mm
length via-hole area
W1
0.5
mm
width micro stripline
W2
1.0
mm
width via-hole area
D1
0.4
mm
diameter of via-hole
1999 Dec 22
4
Philips Semiconductors
Application information
2.4 GHz low noise amplifier with the BFG480W
BOARD LAYOUT
Short-circuit wires are used to adapt an existing printed-circuit board, which was developed for low noise applications.
The layout has been designed with the Hewlett Packard Microwave Design System (HP-MDS).
handbook, full pagewidth
input
C1
µS2
output
C2
TR1
R1
Vsupply
C4
L1
µS1
R2
C3
MGS629
Fig.2 PCB layout.
MEASUREMENTS
The measurements have been done under the following conditions (unless otherwise specified):
• Supply voltage 3.6 V
• Supply current 40 mA
• Frequency 2.4 GHz.
Table 3
Measuring results of the 2.4 GHz LNA
SYMBOL
PARAMETER
CONDITION
VALUE
UNIT
s212
insertion power gain
9.6
VSWRIN
input voltage standing wave ratio
1.6
VSWROUT
output voltage standing wave ratio
1.6
NF
noise figure
3.0
dB
IP3i
third order intercept point
17
dBm
1999 Dec 22
Pi = −10 dBm; ∆f= 200 kHz
5
dB
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