2.45 GHz power amplifier with the BFG480W

APPLICATION INFORMATION
2.45 GHz power amplifier
with the BFG480W
Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
ABSTRACT
• Description of the product
The BFG480W, one of the Philips double polysilicon wideband transistors of the BFG400 series. These transistors are
characterised by a transition frequency higher than 20 GHz at low supply voltages.
• Application area
Low voltage high frequency wireless applications.
• Presented application
A power amplifier for a 2.45 GHz WLAN.
• Main results
At a frequency of 2.45 GHz, a supply voltage of 3.0 V, and a control voltage of 3.0 V, the amplifier delivers an output
power of 19 dBm at an input power of 8 dBm, with a power added efficiency of 38 %.
 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
owner.
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 03
2
Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
INTRODUCTION
With the Philips double polysilicon wideband transistor BFG480W, it is possible to design Power Amplifiers (PAs) for high
frequency applications with a low current and a low supply voltage. The transistors have a transition frequency higher
than 20 GHz at low supply voltages. This application note gives an example of a power amplifier with the BFG480W for
a frequency of 2.45 GHz for a Wireless Local Area Network (WLAN).
PERFORMANCE OVERVIEW
The measurements on the amplifier in the Continuous Wave (CW) mode of operation have been done under the following
conditions:
• Vsupply = 3.0 V
• Vcrtl = 3.0 V
• Isupply = 64 mA
• Pi = 8 dBm
• f = 2.45 GHz
• Zi =50 Ω; Zo = 50 Ω.
Table 1
Measuring results of the PA (CW mode of operation)
SYMBOL
PARAMETER
CONDITIONS
VALUE
UNIT
Po
output power
19
dBm
GP
power gain
11
dB
ηPA
power added efficiency
note 1
38
%
ηtot
total efficiency
note 2
41
%
VSWRIN
input voltage standing wave ratio
2
Notes
1.
Po – Pi
The power added efficiency is defined as η PA = ----------------------------------------× 100% .
V supply × I supply
2.
Po
The total efficiency is defined as η tot = ----------------------------------------× 100% .
V supply × I supply
1999 Dec 03
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Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
CIRCUIT DESCRIPTION
The power amplifier operates at a single supply voltage of 3.0 V. It consists of the BFG480W wideband transistor,
operating in class AB. Biasing for load power adjustment is performed by an external control voltage and a circuit with
an NPN transistor BC817. The BFG480W has two emitter-leads which have to be carefully grounded to ensure stable
operation and performance according to the specification. The PCB layout (see Fig.2) of the amplifier results in an
emitter-to-ground inductance of 130 pH (typical value).
CIRCUIT DIAGRAM
handbook, full pagewidth
Vsupply
Vctrl
R1
L1
R3
R2
C7
C6
TR2
µS4
C3
µS3
µS1
input
50 Ω
µS2
C1
C4
TR1
C2
MGS763
Fig.1 Circuit diagram.
1999 Dec 03
C5
4
output
50 Ω
Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
COMPONENT LIST
Table 2
Component list for the 2.45 GHz PA
COMPONENT
VALUE
UNIT
SIZE, MANUFACTURER
PURPOSE, COMMENT
TR1
BFG480W
SOT343R Philips
RF transistor
TR2
BC817
SOT23 Philips
NPN bias transistor
R1
680
Ω
0.4 W metal film resistor
R2
10
Ω
0.4 W metal film resistor
R3
5
Ω
0.4 W metal film resistor
C1
6.8
pF
type 100A; see note 1
C2
2.2
pF
type 100A; see note 1
C3
6.8
pF
type 100A; see note 1
C4
1.2
pF
type 100A; see note 1
C5
6.8
pF
type 100A; see note 1
C6
6.8
pF
type 100A; see note 1
C7
4.7
nF
type 100A; see note 1
L1
4S2
µS1
−
L = 18 mm;
W = 0.25 mm
micro stripline; Zo ≈ 100 Ω
µS2
−
L = 18 mm;
W = 0.25 mm
micro stripline; Zo ≈ 50 Ω
µS3
−
L = 18 mm;
W = 0.25 mm
micro stripline; Zo ≈ 50 Ω
µS4
−
L = 18 mm;
W = 0.25 mm
micro stripline; Zo ≈ 100 Ω
PCB
−
ferroxcube chip bead
εr ≈ 6.15; d = 0.64 mm
Note
1. Multilayer ceramic chip capacitor; American Technical Ceramics or a capacitor of the same quality.
1999 Dec 03
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Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
BOARD LAYOUT
The double copper-clad PFTE fibre-glass dielectric printed-circuit board has the following specification:
• d = 0.64 mm
• t = 35 µm (copper cladding thickness)
• εr = 6.15
• tan δ = 0.0019
• Dimensions 35 × 45 mm.
handbook, full pagewidth
Vsupply
R1
L1
TR2
R2
SOT343
R3
C7
C6
C3
µS1
µS4
C1
C5
µS2
µS3
C2
TR1
C4
output
PH96076
input
MGS764
Fig.2 PCB layout.
1999 Dec 03
6
Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
MEASUREMENTS
The measurements in the CW mode of operation have been done under the following conditions:
• Supply voltage 3.0 V
• Control voltage 3.0 V
• Quiescent current 1 mA
• Frequency 2.45 GHz.
The output is optimized for an output level of 19 dBm.
Table 3
Measuring results of the 2.45 GHz power amplifier
ηPA
(%)
ηtot
(%)
Pi
(dBm)
Po
(dBm)
GP
(dB)
Isupply
(mA)
0
6.40
6.40
15
7.48
9.70
1
8.80
7.80
19
11.10
13.31
2
10.90
8.90
24
14.89
17.09
3
12.70
9.70
28
19.79
22.17
4
14.30
10.30
34
23.92
26.39
5
15.80
10.80
41
28.34
30.91
6
17.10
11.10
48
32.85
35.62
7
18.20
11.20
56
36.34
39.33
8
19.00
11.00
64
38.09
41.37
9
19.80
10.80
73
39.98
43.61
10
20.50
10.50
83
41.04
45.06
11
21.10
10.10
94
41.22
45.68
12
21.60
9.60
103
41.65
46.78
13
22.20
9.20
113
43.07
48.96
14
22.70
8.70
126
42.62
49.26
15
23.10
8.10
135
42.61
50.41
16
23.40
7.40
140
42.61
52.09
17
23.70
6.70
142
43.26
55.03
18
23.90
5.90
144
42.22
56.82
19
24.20
5.20
146
41.92
60.05
20
24.30
4.30
149
37.84
60.21
1999 Dec 03
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Philips Semiconductors
Application information
2.45 GHz power amplifier with the BFG480W
MGS765
12
P
(dB)
10
handbook,
G halfpage
45
ηPA
40 (%)
(1)
Po
(dB)
35
30
8
(2)
MGS766
30
handbook, halfpage
20
25
6
20
15
4
10
10
2
5
0
0
0
10
20
Po (dB)
0
30
0
4
8
12
20
16
Pi (dB)
(1) Power gain GP.
(2) Power added efficiency ηPA.
Fig.3
Power gain and power added efficiency as
a function of output power.
1999 Dec 03
Fig.4 Output power as a function of input power.
8