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3A325
Surface Mount Balun
VER9/22/00
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(R) 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 (R) 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.
3A325
* * *
MECHANICAL OUTLINE:
ELECTRICAL SPECIFICATIONS:
3A325 - Surface Mount Balun
Parameter Operating Frequency Unbalanced Port Impedance Balanced Port Impedance (2o3) Unbalanced Port Return Loss Insertion Loss (max) Output Amplitude Balance (p-p) Phase Balance Power Rating (max) JC Specification 450-860 MHz 50 50 (25 to Ground) -15 dB 0.35 dB 0.5 dB 180 + 5 degrees 275 Watts CW 4.4 oC/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, -55oC to +85oC. Unit will operate to +125oC with minor degradation in Insertion Loss performance. Specifications subject to change without notice.
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
Data Sheet VER9/22/00 o
TYPICAL PERFORMANCE: (@ 25 C on test board)
Amplitude Balance 3A325
0.4
0
Input Return Loss 3A325
-5
Amplitude Balance [dB]
0.2
-10 Return Loss [dB]
0.0
-15
-20
-0.2
-25
-0.4 470
-30
570
670 Frequency [MHz]
770
870
470
570
670 Frequency [MHz]
770
870
Insertion Loss 3A325
0.0
185
Phase Balance 3A325
183
Insertion Loss [dB]
-0.1
Phase Balance [degrees] 181
-0.2
179
-0.3
177
-0.4 470
570
670 Frequency [MHz]
770
870
175 470
570
670 Frequency [MHz]
770
870
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. 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.
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
Page 2 of 3
Available on Tape and Reel For Pick and Place Manufacturing.
USA/Canada: Toll Free:
(315) 432-8909 (800) 544-2414
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 pushpull networks are combined. Otherwise, the signals would cancel at the output port. PIN CONFIGURATION

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

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
The internal configuration of the Xinger(R) 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(R) 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.
Suggested Board Layout
Page 3 of 3
Available on Tape and Reel For Pick and Place Manufacturing.
USA/Canada: Toll Free:
(315) 432-8909 (800) 544-2414

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