3A325
Surface Mount Balun
VER9/22/00
Page 1 of 3
Available on Tape and
Reel For Pick and
Place Manufacturing.
USA/Canada:
Toll Free:
(315) 432-8909
(801) 544-2414
3A325
Features:
450 860 MHz
180
Transformer
50 Ohm to 25 Ohm
Broad Band
Low Insertion Loss
High Power
Even Order Harmonic
Suppression
Input to Output DC
Isolation
Surface Mountable
Tape & Reel
Convenient Package
Description:
The 3A325 is a low profile balanced to unbalanced transformer
designed for push-pull amplifiers in an easy to use surface
mount package for NMT450 and TV broadcast applications.
These compact Xinger
surface mount baluns are ideal for high
volume manufacturing and are more reliable and repeatable
than traditional baluns. The 3A325 has an unbalanced port
impedance of 50
and balanced port impedances of 25
to
ground with a 50
balance between outputs. This eases the
matching of the push-pull amplifier's power transistors, which
have low impedance levels. The output ports have equal
amplitude (-3dB) with 180 degree phase differential. The Xinger
balun is a result of years of research and development
culminating with a solution so unique, a patent is pending on the
design approach. The 3A325 is available on tape and reel for
pick and place high volume manufacturing.
MECHANICAL OUTLINE:
ELECTRICAL SPECIFICATIONS:
3A325 - Surface Mount Balun
Parameter
Specification
Operating Frequency
450-860 MHz
Unbalanced Port Impedance
50
Balanced Port Impedance (2
3)
50
(25
to Ground)
Unbalanced Port Return Loss
-15 dB
Insertion Loss (max)
0.35 dB
Output Amplitude Balance (p-p)
0.5 dB
Phase Balance
180 + 5 degrees
Power Rating (max)
275 Watts CW
JC
4.4
o
C/Watt
Specifications based on performance of units installed in an RF microstrip test fixture. 50 ohms nominal input impedance, and 25 ohm nominal
output impedance. Temperature of operation, -55
o
C to +85
o
C. Unit will operate to +125
o
C with minor degradation in Insertion Loss
performance. Specifications subject to change without notice.
3A325
Data Sheet VER9/22/00
Page 2 of 3
Available on Tape and
Reel For Pick and
Place Manufacturing.
USA/Canada:
Toll Free:
(315) 432-8909
(800) 544-2414
TYPICAL PERFORMANCE: (@ 25
o
C on test board)
Amplitude Balance 3A325
-0.4
-0.2
0.0
0.2
0.4
470
570
670
770
870
Frequency [MHz]
Amplitude Balance [dB]
Input Return Loss 3A325
-30
-25
-20
-15
-10
-5
0
470
570
670
770
870
Frequency [MHz]
Return Loss [dB]
Insertion Loss 3A325
-0.4
-0.3
-0.2
-0.1
0.0
470
570
670
770
870
Frequency [MHz]
Insertion Loss [dB]
Phase Balance 3A325
175
177
179
181
183
185
470
570
670
770
870
Frequency [MHz]
Phase Balance [degrees]
PERFORMANCE DATA:
Due to the fact the output impedances of the balun are 25
to ground, a circuit board was produced to transform the
output impedances back to 50
in order to test the phase
and amplitude balance of the balun (see plots above). The
test fixture is shown below. This wideband transformer has a
Chebychev characteristic response.
The unbalanced port return loss plot was measured at the
input of the aforementioned test board. Unbalanced port
return loss performance can be improved as narrow band
matching is performed at the output of the balun (input of
the transistor).
The insertion loss measurement was taken by connecting
two baluns back to back and a true insertion loss
measurement was collected, the fixture is shown below.
The insertion loss was calculated by taking the
transmission loss
of the board
assembly and
factoring out
reflected loss and,
since there are
two baluns on the
test board, that
result was then halved.
3A325
Data Sheet VER9/22/00
Page 3 of 3
Available on Tape and
Reel For Pick and
Place Manufacturing.
USA/Canada:
Toll Free:
(315) 432-8909
(800) 544-2414
One very important point worth noting: it is strongly
recommended, when implementing the surface mount balun,
that pin 1 of the first balun is offset from pin 1 of the opposing
balun, note the above test board with two mounted baluns.
This insures proper phase relationships for the combining of
signals. This convention
must be followed if multiple push-
pull networks are combined. Otherwise, the signals would
cancel at the output port.
PIN CONFIGURATION
Surface Mount Balun Layout
The internal configuration of the Xinger balun is diagramed
above, the unbalanced port is DC connected to ground and
the two balanced ports have DC continuity with each other.
The DC isolation between the balanced ports and the
unbalanced port has some advantages, such as added
transistor protection from any DC surges (e.g. lightning)
which may be applied to the unbalanced port. Also, there is
an opportunity to share DC biasing of the transistors at the
balanced ports (dependent upon transistor repeatability),
improving overall reliability. The construction is bonded
multilayered stripline made of low loss dielectric with plated
through vias connecting the internal circuitry to the external
printed circuit board, similar to that of the Xinger hybrids
and directional couplers.
MOUNTING
In order for Xinger surface mount components to work
optimally, there must be a 50
transmission line to the
balanced port and 25
transmission lines from the
unbalanced ports. Also, there must be a very good ground
plane under the balun to insure proper electrical performance.
If either of these two conditions are not satisfied, amplitude
balance, insertion loss and VSWR may not meet published
specifications.
Overall ground is improved if a dense population of plated
through holes connect the top and bottom ground layers of
the PCB (Printed Circuit Board). This minimizes ground
inductance and improves ground continuity. All of the
Xinger components are constructed from ceramic filled
PTFE composites which possess excellent electrical and
mechanical stability having X and Y thermal coefficient of
expansion (CTE) of 17 ppm/
o
C
When a surface mount balun is mounted to a printed circuit
board, the primary concerns are; insuring the RF pads of
the device are in contact with the circuit traces of the PCB
and insuring the ground plane of neither the component nor
the PCB is in contact with the RF signal. As long as the
geometry of the unit fits onto the layout of the circuit trace
on the PCB, and the conditions of the previous paragraph
are followed, the balun's performance is ensured. An
example of how the PCB footprint could look is shown
below. In specific designs, the transmission line widths
need to be adjusted to the unique dielectric coefficients
and thicknesses as well as varying pick and place
equipment tolerances.
Suggested Board Layout
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