3A325 Datasheet, PDF (3/3 Pages) List of Unclassifed Manufacturers – Surface Mount Balun

3A325
Data Sheet VER9/22/00
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.
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/^oC
PIN CONFIGURATION
Ω
λ
Ω
λ
Ω
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.
Surface Mount Balun Layout
Ω
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
Ω
transistor protection from any DC surges (e.g. lightning)
Ω
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 50Ω transmission line to the
balanced port and 25Ω 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.
Suggested Board Layout
Page 3 of 3
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