Application Note

VISHAY VITRAMON
Multilayer Chip Capacitors
Application Note
VJ 6040 Mobile Digital TV UHF Antenna Evaluation Board
GENERAL
Tuning circuit key features are:
VJ 6040 is a multilayer ceramic chip antenna designed for
receiving mobile digital TV transmissions in the UHF band.
The target application for the VJ 6040 antenna is the cellular
phone. For this reason the following document refers to an
antenna configuration small enough to fit into most cellular
phones. Applications that allow larger ground planes can
enjoy improved antenna efficiency.
To help in the design-in process, Vishay offers an antenna
evaluation board by which designers can test the antenna
performance. The evaluation board measures 40 mm by
90 mm and includes the following features:
• VJ 6040 antenna mounted against a 40 mm by 80 mm
ground plane
• Small outline - fits into a single side PCB of 5 mm x 5 mm
• Low cost BOM
• Digitally controlled - two digital control pins enable
covering the entire band, by offering 4 combinations
• Also serves as a matching circuit reflecting a 50 Ω
impedance
SCHEMATICS
Figure 1 presents the schematic
recommended tuning circuit.
drawing
of
the
VJ 6040
• Active digital tuning circuit controlled by two input lines
• 50 Ω SMA termination
This document describes in detail the structure of the active
digital tuning circuit needed to allow full coverage of the UHF
band. It continues by describing a reference ground plane
configuration. Designers who wish to make modifications
in the values presented hereafter are encouraged to
take advantage of the technical support offered by
Vishay Vitramon division.
L1
L3
Digital Input 1
D1
C1
For any technical support please contact: [email protected]
R1
D2
VJ 6040 TUNING CIRCUIT
L2
This section in the document describes the recommended
tuning circuit, as designed by Vishay Vitramon.
Document Number: 45165
Revision: 06-Jul-09
L4
C3
Digital Input 2
C4
C2
50 Ω RF feed
Fig. 1 - Tuning Circuit Schematics
For technical questions, contact: [email protected]
www.vishay.com
1
APPLICATION NOTE
The aggressive antenna miniaturization process that
resulted in the ultra-small form factor of the antenna also had
the unwanted effect of reducing the antenna bandwidth to
approximately 120 MHz at - 3 dBi from its peak value. Full
coverage of the UHF band (470 MHz to 860 MHz) can be
achieved by implementing a simple four channel active
digital tuning circuit. The tuning circuit shifts the central
operating frequency of the antenna, thus allowing full
coverage of the UHF band. Applications that require partial
coverage of the UHF band can enjoy improved radiation
efficiency by removing the tuning circuit and setting the
antenna central frequency to the desired value using passive
components.
Application Note
Vishay Vitramon
VJ 6040 Mobile Digital TV UHF Antenna Evaluation Board
LAYOUT
Figure 2 shows the recommended layout of the tuning circuit. Layout should be as compact as possible. The striped area is GND
plane.
VISHAY
VJ 6040
Digital Input 1
L3
L1
C1
D2
L2
R1
Via To GND
D1
C4
C3
L4
Digital Input 2
Via To GND
C2
50 Ω Line
To The Receiver
APPLICATION NOTE
Fig. 2 - Tuning Circuit Layout
TABLE 1 - BOM OF THE TUNING CIRCUIT
COMPONENT
DESCRIPTION
VALUE
VENDOR
L1
Inductor
47 nH
Vishay
L2
Inductor
39 nH
Vishay
L3, L4
Inductor
120 nH
Taiyo Yuden
C1, C4
Capacitor
2.2 pF
Vishay
C2, C3
Capacitor
220 pF
Vishay
R1
Resistor
1 kW
Vishay
D1, D2
PIN diode
www.vishay.com
2
Infineon
For technical questions, contact: [email protected]
PART NUMBER
HK 1005 R12J
????
Document Number: 45165
Revision: 06-Jul-09
Application Note
Vishay Vitramon
VJ 6040 Mobile Digital TV UHF Antenna Evaluation Board
ELECTRICAL CHARACTERISTICS AND FUNCTIONAL DESCRIPTION
The tuning circuit herein is effectively an inductor, connected
in series with a capacitor. The total impedance generated by
this circuit can be described in the following equation
(excluding the capacitors C2, C3 and C4):
Z = Z L + Z C + Z L = j * (ω L 1 −
1
1
2
ω = 2π f
1
ω C1
+ ω L 2)
By connecting PIN diodes in parallel to C1 and L2, the tuning
circuit can electrically short-circuit one of the two reactants or
both. Table 2 is detailing all logical states of the tuning circuit,
and the electrical effect as presented in the impedance Z. For
the sake of small signal analysis, when the PIN diode is in
forward conductance mode, it is represented as a 2 Ω
resistor.
TABLE 2 - TUNING CIRCUITS' IMPEDANCES
DIGITAL INPUT 1
DIGITAL INPUT 2
PIN 0
PIN 1
0
0
High Z
High Z
0
1
High Z
Z (W)
j * ( ω L1 −
1
ω C1
j * ( ω L1 −
2W
+ ω L2 )
1
)+ 2
ω C1
1
0
2W
High Z
j * ( ω L1 + ω L2 ) + 2
1
1
2W
2W
j * ω L1 + 4
As evident from table 2, each one of the 4 possible logic
states represents a different tuning circuit between the
antenna and the receiver port.
By applying the values shown in table 1 to L1, C1 and L2 the
4 states cover the entire UHF band.
SELECTING THE RESISTIVE VALUES OF R
R1 resistor is used to DC bias the PIN diodes. Selecting the
value for R1 can be derived for the following equation:
Vcontrol - Vd
Id
Let's assume that the digital control line is 1.8 V when high.
To allow a current of 1 mA, R1 should be set as follows:
When:
R = resistive value (in Ω) for R1
Vcontrol = control voltage (in volts) as generated by the
controller
Vd = forward voltage (in V) generated on the PIN diode when
biased
R1 =
1 .8 - 0 .8
= 1 kΩ
0 . 001
Id = forward current (in A) through the PIN diode when biased
Document Number: 45165
Revision: 06-Jul-09
For technical questions, contact: [email protected]
www.vishay.com
3
APPLICATION NOTE
R =
Example:
The PIN diode should be forward biased at 0.8 V to allow just
over 1 mA to pass through it (see the graphs below). At 1 mA,
the diode small signal impedance drops to its required value
of 2 Ω.
Application Note
Vishay Vitramon
VJ 6040 Mobile Digital TV UHF Antenna Evaluation Board
6
100.00
rf - Forward Resistance (Ω)
IF - Forward Current (mA)
f = 100 MHz
5
10.00
1.00
0.10
4
3
2
1
0
0.01
0.5
18325
0.6
0.7
0.8
0.9
0.1
1.0
VF - Forward Voltage (V)
100
10
1.0
IF - Forward Current (mA)
18341_1
Fig. 3
Figure 3 displays the ???? PIN diode characteristics.
GROUND PLANE CONFIGURATION
General
40 mm
15.5 mm
VISHAY
VJ 6040
Tuning
Circuit
50 Ohm
An important consideration in the design of this product into
cell phone applications is the coexistence of the cell phone
antenna with VJ 6040. The recommended ground plane
configuration presented below includes recommendations
regarding how to set the cellular antenna relative to the
VJ 6040 to minimize losses to both antennas.
Receiver
Figure 4 describes a recommended reference ground plane
configuration.
90.5 mm
77 mm
VJ 6040 evaluation board demonstrates exceptional antenna
performance achieved with a 40 mm by 80 mm ground plane.
APPLICATION NOTE
10.5 mm
Additional
antenna
3 mm
The VJ 6040 antenna is unbalanced, therefore requiring a
ground plane for its operation. The ground plane dimensions
significantly influence the antenna performance. The rule of
thumb in unbalanced antenna ground plane design is that
antenna efficiency increases with ground plane size. The
evaluation board demonstrates how the antenna complies
with the EMBRAI standard when set against a ground plane
small enough to fit into most cellular phone designs.
Applications that allow larger ground planes can enjoy higher
efficiency.
The areas marked in green in the close proximity to the
antenna should remain empty from large conducting
surfaces including ground planes (outer or inner layers),
batteries, connectors, buttons, or other large components.
Applications that require additional antennas, such as cell
phones, should position the cellular antenna at the top left
hand side while maintaining maximum distance from
VJ 6040. The presence of an additional antenna might cause
loss of efficiency to both antennas.
Fig. 4 - Recommended Ground Plane
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4
For technical questions, contact: [email protected]
Document Number: 45165
Revision: 06-Jul-09
Application Note
Vishay Vitramon
VJ 6040 Mobile Digital TV UHF Antenna Evaluation Board
Features are subject to revisions or changes without notification
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 6040
VJ6040M011SXISRA0
1000 pieces
For technical questions, contact: [email protected]
www.vishay.com
5
APPLICATION NOTE
Document Number: 45165
Revision: 06-Jul-09
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