DEMO-HMPP-389T Datasheet, PDF (7/12 Pages) Broadcom Corporation. – MiniPak Surface Mount RF PIN Switch Diodes

Testing the HMPP-389T on the Demo‑board
Introduction
The HMPP-389T PIN diode is a high frequency shunt switch.
It has been designed as a smaller and higher performance
version of the HSMP-389T (SC-70 package).
The DEMO-HMPP-389T demo-board allows customers
to evaluate the performance of the HMPP‑389T without
having to fabricate their own PCB. Since a shunt switch’s
isolation is limited primarily by its parasitic inductance, the
product’s true potential cannot be shown if a conventional
microstrip pcb is used. In ­order to overcome this problem,
a coplanar waveguide over ground-plane structure is
used for the demo-board. The bottom ground-plane is
connected to the upper ground traces using multiple
via-holes.
A 50Ω reference line is provided at the top to calibrate the
board loss. The bottom line allows the HMPP‑389T diode
to be tested as a shunt switch.
Figure 13. Soldering details of connector ­fingers to upper ground plane.
reference line
Agilent
SK063A
test line
HMPP-389T
Figure 12. Demo-board DEMO-HMPP-389T.
Figure 14. Soldering details of connector ­fingers to lower ground plane.
Test Results
Measurements of the reference line’s return and insertion
losses were used to gauge the effectiveness of the VSWR
mitigating steps. In our prototype, the worst case return
loss of the reference line was 20 dB at 5 GHz (Figure 20).
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Demo-board Preparation
Since the performance of the shunt switch is ultimately
limited by the demo-board, a short discussion of the
constructional aspects will be beneficial. Edge-mounted
SMA connectors (Johnson #142-0701-881) were mounted
on both the reference and test lines. A special mounting
technique has been used to minimize reflection at the pcb
to connector interface. Prior to mounting, the connector
pins were cut down to two pin diameters in length. Subse-
quently, the connector fingers were soldered to the upper
ground plane (Figure 18). Solder was filled between the
connector body and fingers on the lower ground plane
until the small crescent of exposed teflon was completely
covered (Figure 19).
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FREQUENCY (GHz)
Figure 15. Swept Return Loss of Reference
Line.
Figure 15. Swept return loss of reference line.