Philips Semiconductors B.V.
1
Gerstweg 2, 6534 AE Nijmegen, The Netherlands
R epor t nr . : RNR-T45-97-B-0688
Author : T . Bus s
D a te : 26 Aug 1997
D epa r tm ent : P.G. T r a nsi sto r s & D i ode s, D evel op m ent
900MHz DRIVER-AMPLIFIER
WITH ENABLE-SWITCH
USING THE B FG425W
Abstract:
This application note contains an example of a Driver-Amplifier using the new BFG425W Double Poly RF-
transistor. The driver can be switched on and off with a control-voltage VCON=0...3V. The driver is designed
for a frequency f=900MHz.
Performance at f=900MHz, T=250C: Power Gain >12dB.
Appe ndix I : Sc hemati c of th e c i rcui t
Appendix II: R esults of m easur em ents
Appendix III: Pr i ntl a y out a nd li st of u s ed com ponents & m ater ia l s
Philips Semiconductors B.V.
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Introduction:
With the new Philips silicon bipolar double poly BFG400W series, it is possible to design driver-amplifiers
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. In this note an example of such an
amplifier for 900MHz will be given. This driver can be switched on and off with a control-voltage VCON.
Designing the circuit:
T he cir cui t i s d esi gned to s how the fol l owi ng per for m a nce ( ta r get):
tr ansistor : BF G 425W
VSUP=3V, V CON=0V ( d r i ver disabl ed) , ISUP~0mA
VSUP=3V, V CON=3.0V (driver enabled), ISUP~11mA
freq=900MHz
Power Gain: >12dB
VSWRi<1:2.5
VSWRo<1:2
T he in - and outputm atc hing - c ir cuits ar e r ea l i sed w i th a R C- com binati on. No coi ls a r e used to r educe the price.
T he En abl e i s c o ntr oll ed at the ba se i n or der to r educe the c ontr ol - cur rent ( VCON=3V : I CON~0.6mA). DC-
decoup l i ng i n th e em i tter i s used r e duce the infl uence o f H FE- spr e a d.
De signi ng the l ayout:
A l a y -out ha s be en des igne d w i th H P-M D S. Appen di x III contains the printlayout.
Measurements:
M ea s urem ents of the total c ir cuit ( epoxy PC B) ar e done (Appendi x II) .
Philips Semiconductors B.V.
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Appe ndix I : Sc hemati c of th e c i r cui t
Figure 1: Driver circuit
900M H z D r iver Co m ponent list:
Component: Value: Comment:
R 1 2.7 kΩBias, RF-block
R 2 100 ΩRF-block
R 3 3.9 kΩBias.
R 4 56 ΩDC-decoupling
C 1 150 pF Input m a tch.
C 2 150 pF Output ma tch.
C 3 27 pF 900M H z shor t.
C4 1 nF RF Dec oupling
C 5 27 pF 900M H z shor t.
C6 1 nF RF Dec oupling
C 7 27 pF 900M H z shor t.
BFG425W
+VSUP
OUT
50Ω
IN
50Ω
C1
C2
C4
R1
R2
C3
C6
C5
+VSUP
+VCON
R4 C7
R3
Philips Semiconductors B.V.
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Appe ndix II: Results mea sure ments:
BF G425 W, VSUP=3.0V, I SUP~11.0mA@T=25oC ,VCON=3.0V, I CON~0.6mA@T=25oC
Measurements PCB: Comment:
f=900MHz
|S21|2 [dB] 15.5 PIN=- 30dBm , T =25oC
GP [dB] 13 PIN=- 10dBm , T =25oC
GP [dB] ~11 PIN=-10dBm, T ≈ -40oC (Freeze spray)
VSWRi 2.5 PIN=- 30dBm , T =25oC
VSWRo 1.7 PIN=- 30dBm , T =25oC
N oi se Figur e [dB] ~2.5 PIN=- 30dBm, T =25oC
IP3 [dBm ] ( output) - not m ea sur ed
Figure 2: ISUP and S21 as funcion of VCON. (VSUP=3.0V, f=900MHz)
Isup and S21 as function o
0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.5 3 3.5
Vcon [V
S21
Isu
p
Philips Semiconductors B.V.
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Appe ndix III: Pr i nt l ayout a nd l i st of used com pon ents & m a ter ia l s
F igur e 3: Pr i ntla yout
900M H z D r iver Co m ponent list:
Component: Value: size:
R 1 2.7 kΩ0603 P hilips
R 2 100 Ω0603 Philips
R 3 3.9 kΩ0603 P hilips
R 4 56 Ω0603 Philips
C 1 150 pF 0603 Philips
C 2 150 pF 0603 Philips
C 3 27 pF 0603 Philips
C 4 1 nF 0603 Philips
C 5 27 pF 0603 Philips
C 6 1 nF 0603 Philips
C 7 27 pF 0603 Philips
P5 BFG425W SOT343R Philips
PCB εr ~4.6, H=0.5m m F R4
note 1: T he u sed PC B w as designed for Low Noi se Am pl ifi er a ppl icati ons. Shor ts a nd wi r es ar e used to adapt
the PCB for this dr iver a p pl i ca tion.
SHORT
R1
C2
C1
R2
Vsup
RFout
RFin
900MHz Driver Amplifier with enable-switch
BF
G
42
5W
P5
C3
µS4
µS4
C4
Vcon R4
R3
C5, C6
C7
