Application Note

VISHAY VITRAMON
Ceramic Chip Antenna
Application Note
VJ 3505 GSM Interference Immune Tuning Circuit
Vishay offers an evaluation kit fitted with the GSM immune
tuning circuit and the VJ 3505 miniature UHF antenna to
allow designers to measure the antenna parameters.
For any technical support please contact: mlcc@vishay.com
VJ 3505
Tuning
Circuit
GSM
UHF
Connector Connector
Port 2
VJ 3505 is a narrow band antenna that requires an active
digital tuning circuit to allow it to cover the UHF band which
spans between 470 MHz and 860 MHz. The tuning circuit
typology is designed to withstand external interference such
as GSM transmission. Nevertheless, in cases where the
GSM transmitter is in close proximity to VJ 3505, the tuning
circuit typology should be modified to eliminate the risk of
antenna detuning. The following document describes in
detail the GSM interference immune tuning circuit.
GSM Antenna
Port 1
VJ 3505 GSM INTERFERENCE IMMUNE
TUNING CIRCUIT
CHOOSING THE CORRECT TUNING CIRCUIT
Vishay Vitramon division provides two tuning circuit
reference designs:
• Standard tuning circuit - described in detail in a separate
application note titled “EVK 3505 User Guide”
Network Analyzer
S12
• Active digital tuning circuit controlled by two input lines
allowing full coverage of the UHF band 470 to 860 (MHz)
• GSM immune tuning circuit - described hereafter
The standard typology enables excellent antenna
performance while maintaining minimal cost. However, the
standard tuning circuit can withstand GSM interference up to
0 dBm, measured at the VJ 3505 antenna feed. The power
received by VJ 3505 can be measured using the test setup
described in figure 1.
Fig. 1 - Test Setup
Once the coupling factor is measured, the received power at
the VJ 3505 feed can be estimated as follows:
Received Power = Transmitted Power + Coupling Factor
Example:
If the GSM peak power output is + 33 dBm and the coupling
factor was found to be - 15 dB then the maximum received
power would be + 18 dBm.
The GSM immune tuning circuit should be used in cases
where the peak received power is greater than 0 dBm.
Document Number: 45186
Revision: 08-Jul-10
For technical questions, contact: mlcc@vishay.com
www.vishay.com
45
APPLICATION NOTE
A test PCB should be designed to accommodate both
VJ 3505 and the GSM antennas. The two antennas should
be positioned as far from each other as allowed by the
mechanical constraints of the application. Using a network
analyzer, the coupling between the antennas can be directly
measured for each of the four channels offered by the tuning
circuit. The same test setup can later be used to fine tune the
tuning element components to negate any detuning caused
by the GSM antenna, or other nearby components.
Application Note
Vishay Vitramon
VJ 3505 GSM Interference Immune Tuning Circuit
GSM IMMUNE TUNING CIRCUIT TOPOLOGY
SCHEMATICS
Figure 2 presents the schematic drawing of the recommended tuning circuit.
VJ 3505
L1
R1
L4
D1
Digital input 1
L2
C3
R2
L5
L3
D2
Digital input 2
C4
R3
C1
L6
C2
50 Ω RF
feed
APPLICATION NOTE
Fig. 2 - Tuning Circuit Schematics
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46
For technical questions, contact: mlcc@vishay.com
Document Number: 45186
Revision: 08-Jul-10
Application Note
Vishay Vitramon
VJ 3505 GSM Interference Immune Tuning Circuit
LAYOUT
Figure 3 shows the recommended layout of the tuning circuit. Layout should be as compact as possible.
Antenna not in scale
L1
Digital input 1
D1
R1
L4
L2
D2
R2
L5
Digital input 2
L3
C3
C4
R3
L6
C1
L4
C2
50 Ω line
Legend
Conducting strip lines
0402 component
Via hole to ground plane
Fig. 3 - Tuning Circuit Layout
Document Number: 45186
Revision: 08-Jul-10
For technical questions, contact: mlcc@vishay.com
www.vishay.com
47
APPLICATION NOTE
Ground plane copper area on top, bottom and/or inner layers
Application Note
Vishay Vitramon
VJ 3505 GSM Interference Immune Tuning Circuit
LAYOUT GUIDELINES
1. The distance between the tuning circuit components should be minimized
2. Inductor L1 should be located as close as possible to the antenna
3. Inductors L4 and L5 should be as close as possible to the PIN diodes
4. It is recommended to remove all ground planes from under the tuning circuit. The ground plane should be added to insure a
50 Ω wave guide after capacitor C1
REFERENCE TUNING CIRCUIT BOM
TABLE 1 - TUNING CIRCUIT BILL OF MATERIALS
QUANTITY PER
CIRCUIT
PART NUMBER
MANUFACTURER
L4, L5, L6
3
HK 1005 R12J-T
Taiyo Yuden
D1, D2
2
BAR63-06W
Infineon
15 nH
L1
1
IMC0402ER15NJ
Vishay
12 nH
L2
1
IMC0402ER12NJ
Vishay
27 nH
L3
1
IMC0402ER27NJ
Vishay
3.9 pF
C1
1
VJ0402A3R9BXACW1BC
Vishay
VALUE
REFERENCE
120 nH
PIN diode
220 pF
C2, C3, C4
3
VJ0402A221JXACW1BC
Vishay
330 Ω
R1, R2, R3
3
CRCW0402330RFKED
Vishay
Note
• Any changes made in the reference BOM might result in loss of radiation efficiency.
CONTROL SIGNAL INTEGRITY
The following table describes the desired control signal properties:
TABLE 2 - SIGNAL INTEGRITY FOR ELECTRICAL CONTROL ALTERNATIVE
PARAMETER
SYMBOL
MIN.
TYP.
MAX.
UNITS
COMMENTS
Equivalent DC Circuit
Logical LOW
Vil
- 0.3
0
0.2
V
APPLICATION NOTE
Equivalent DC Circuit
Logical HIGH
Source current
Sink current
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48
Vih
3
3.3
5
V
Isource
4
4.2
5
mA
Vin = 5 V
Diode reverse leakage
current
Isink
0
0.01
0.05
mA
Vin = - 0.3 V
For technical questions, contact: mlcc@vishay.com
Document Number: 45186
Revision: 08-Jul-10
Application Note
Vishay Vitramon
VJ 3505 GSM Interference Immune Tuning Circuit
CHANNEL CHARACTERISTICS
The two digital control lines offer four frequency channels as described in table 3 below. This table shows the typical peak gain
obtained in each of the four channels.
TABLE 3 - PEAK GAIN OBTAINED IN EACH OF THE FOUR CHANNELS
PARAMETER
D1
D2
BAND (MHz)
S11 (dB)
460
5
560
660
760
860
760
860
760
860
760
860
0
-5
1
L
L
470 to 540
- 10
- 15
- 20
- 25
460
5
f (MHz)
560
660
0
-5
2
H
L
540 to 620
- 10
- 15
- 20
- 25
460
5
f (MHz)
560
660
0
-5
3
L
H
620 to 750
- 10
- 15
- 20
- 25
460
5
f (MHz)
560
660
0
-5
4
H
H
750 to 860 (1)
- 10
- 15
- 25
f (MHz)
Note
(1) Applications withstanding strong GSM interference will incorporate a band pass filter designed to filter out the interfering signal. Such a filter
will add significant attenuation above 750 MHz.
The company’s products are covered by one or more of the following:
WO2008250262 (A1), US2008303720 (A1), US2008305750 (A1), WO2008154173 (A1). Other patents pending.
ORDERING INFORMATION
VISHAY MATERIAL
PACKAGING QUANTITY
VJ 3505
VJ3505M011SXMSRA0
1000 pieces
Document Number: 45186
Revision: 08-Jul-10
For technical questions, contact: mlcc@vishay.com
www.vishay.com
49
APPLICATION NOTE
- 20