CDMA CELLULAR VCO WITH THE BFG425W, BFG410W AND VARACTOR BB142

H
Philips Semiconductors B.V.
Gerstweg 2, 6534 AE Nijmegen, The Netherlands
Report nr.
Author
Date
Department
: RNR-45-98-B-0827
: Haris Duric & Robert Cloudt
: 16 December 1998
: DSC-N, Development
CDMA CELLULAR VCO WITH THE BFG425W, BFG410W
AND VARACTOR BB142
Abstract:
This application note contains an example of a Voltage Controlled Oscillator for cellular CDMA applications
with the fifth generation BFG425W and BFG410W Double Poly RF-transistors. The BB142 is a new
varactor specially designed for RF-application with low noise performance. The VCO is designed for the
receive band of the IS-95 standard.
Appendix I: Schematic of the circuit
Appendix II: Printlayout and list of used components & materials
Appendix III: Results of measurements
1
H
Philips Semiconductors B.V.
Introduction:
With the new Philips silicon bipolar double poly BFG400W series, it is possible to design low phase noise
VCO’s for cellular and PCS frequency applications with a low current and a low supply voltage. These
VCO’s are well suited for the new generation low voltage high frequency wireless applications. In this note
an example of such an VCO will be given. This VCO is designed for a center frequency of 881.5 MHz and
a span of 25 MHz.
Designing the circuit:
The circuit is designed to show the following performance:
VSUP=2.7 V
Isup=7.3mA
Center freq=881.5 MHz
Span = 25 MHz
Pout = 3.33 dBm
Phase noise at 60 kHz <= -117 dBc/Hz
VSWRo<2:1
transistor: BFG425W, BFG410W
varactor : BB142
The output matching is realised with a LC-combination in the buffer stage. The matching circuit will also
supress the harmonics somewhat. There’s a trade off between the pulling and the noise performance of the
VCO.
Designing the layout:
A lay-out has been designed with HP-MDS. Appendix II contains the printlayout and component placement.
Measurements:
Measurements of the total circuit (epoxy PCB) have been done. The result can be found in Appendix III.
2
H
Philips Semiconductors B.V.
Appendix I: Schematic of the circuit
Figure 1:VCO circuit
CDMA VCO Component list:
Component:
Value:
C1
47n
C2
3.6p
C3
4.3p
C4
56p
C5
1.2p
C6
3p
C7
47n
C8
56p
C9
56p
C10
47p
C11
1.8p
C12
6.8p
R1
8.2k
R2
22k
R3
390
R4
2k
R5
1k
R6
100
L1
82n
L2
12n
L3
4n
T1
BFG425W
T2
BFG410W
Varactor
BB142
Comment:
DC-filter
Determines tuning range
Determines tuning range
DC-block
Negative impedance
Negative impedance
DC-filter
RF-bypass
RF-bypass
match between VCO and buffer
RF-feed/output match
Output match/filter
Bias
Bias
Bias
Bias
Bias
Better RF-stability (K>1)
RF-choke
Ouput match
Microstripline inductance for better Q
SOT 343
SOT 343
SOD 523
3
H
Philips Semiconductors B.V.
Appendix II: Printlayout and list of used components & materials
GND
Vtune
Vsup
C1
L3
L1
C7
Varactor
C8
C9
R6
C3 C2
R4
R2
R5
C10
C4
R3
R1
C5
T1
C6
T2
C12
L2
C11
RF-out
Figure 2: Printlayout
CDMA VCO Component list:
Component:
Value:
C1
47n
C2
3.6p
C3
4.3p
C4
56p
C5
1.2p
C6
3p
C7
47n
C8
56p
C9
56p
C10
47p
C11
1.8p
C12
6.8p
R1
8.2k
Comment:
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
4
H
Philips Semiconductors B.V.
R2
R3
R4
R5
R6
L1
L2
L3
T1
T2
Varactor
22k
390
2k
1k
100
82n
12n
4n
(W=0.7mm;L=9.6mm)
BFG425W
BFG410W
BB142
0402 Philips
0402 Philips
0402 Philips
0402 Philips
0402 Philips
TDK MLG 1608 SERIES
TDK MLG 1608 SERIES
Microstrip (PCB: εr=4.6,H=0.5mm)
SOT 343
SOT 343
SOD523
5
H
Philips Semiconductors B.V.
Appendix III: Results of measurements:
Samples CDMA VCO's
Specification
Unit
Value
Vcc
Power Consumption
Control Voltage range Min.
Volt
<=mA
Volt
2.7
7.3
0
Control Voltage range Max.
Operating f range Min.
Volt
MHz
2.5
849
MHz
MHz/V
900
17
>=dBm
(+/-dBm)
3.33
0.17
<=dBc
-75
Phase Noise(15KHz)
Phase Noise(30KHz)
<=dBc/Hz
<=dBc/Hz
-105
-111
Phase Noise(60KHz)
<=dBc/Hz
-117
Pushing figure
(Vcc +/-0.3V)
(+/-KHz)
400
Pulling figure
(VSWR=2.0 for all phase, ref:50Ohm)
(+/-KHz)
500
<=dBc
-25
Operating f range Max.
Modulation sensitivity
Output Level
Output level deviation
C/N
Spurious response (Harmonics)
VSWRo
Oscillation guaranteed for VCC =
Width (mm)
Length (mm)
1.8
Volt
2.4<Volt<3
10.25
10.1
6
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