Technological advances lead
to tactical advantages. That’s why investments
in electronic technology for military
applications traditionally run high.
Yet those investments can often yield
useful breakthroughs as well as dramatic
improvements in existing technologies.
Military systems such as electronic warfare
(EW), signal intelligence (SIGINT),
and radar systems receive the most funding.
Still, electronic building blocks such
as amplifiers, display screens, software, and
transistors enable those large systems and,
hopefully, provide that tactical edge.
One of the most basic electronic building
blocks is the transistor. Military system
designers have long sought more power
from a single device to achieve higher
power densities in radar and EW transmitters
for a given size. Two of the more
significant developments in silicon transistor
technology come from companies at
the extremes of the supply curve: Freescale
Semiconductor and HVVi Semiconductors.
The former applies a traditional lateral
silicon device architecture, while the
latter employs a unique vertical configuration
in its novel silicon transistors.
A CLOSER LOOK
Freescale is well established for its
laterally diffused metal-oxide-semiconductor
(LDMOS) devices, especially
for cellular basestations and other commercial
comms systems. By extending
its LDMOS process capabilities to
50-V transistor fabrication, it developed
its model MRF6V14300H transistor for
pulsed military systems, including radar
and avionics systems (Fig. 1).
The Si LDMOS transistor is one of
the first fruits of Freescale’s sixth-generation
Very High Voltage (VHV6) process.
VHV6 is an evolution of the LDMOS
process used to manufacture +28-V dc
parts for commercial broadcast, communications,
industrial, and medical applications,
along with some military systems.
By operating at the higher bias voltage
while maintaining good thermal dissipation,
the MRF6V14300H can deliver
330-W peak output power with 17-dB
power gain from 1200 to 1400 MHz. The
output power is based on pulsed input
signals with 300-µs pulse width with 12%
duty cycle. Under those conditions, the
transistor achieves 60% drain efficiency.
Taking a more unconventional
approach, HVVi uses a vertical transistor
architecture to obtain higher power
levels at high frequencies, but also relies
on a high supply voltage of +48 V dc. The
company’s patented high-voltage vertical
field-effect-transistor (HVVFET) technology
employs the transistor’s foundation
or substrate as the device drain.
The transistor depletes vertically into
the substrate as the supply voltage is fed
to the drain. It approaches planar breakdown
in the vertical drain region, standing
off maximum voltage with minimum
on resistance. The technology forms the
basis for the company’s first three products,
designed for high-power pulsed
applications at L-band frequencies—
Identify Friend or Foe (IFF), TCAS,
TACAN, and Mode-S radar systems.
The lower-frequency PVV1011-300
HVVFET transistor
is designed for 300-W
pulsed output power from
1030 to 1090 MHz. It achieves that
output level with 15-dB power gain and
48% drain efficiency when operating
with 50-µs pulse-width input signals for
a 1-ms pulse period.
The PVV1214-25 and PVV1214-100
HVVFETs provide higher frequency.
The former delivers a 25-W output level
from 1200 to 1400 MHz. The latter is
rated for 100-W output power from 1200
to 1400 MHz. Both are characterized
with 200-µs pulse-width input signals at
a 10% pulse duty cycle.
Building on the HVVFET technology,
HVVi has added a trio of transistors
for airborne distance-measuring-equipment
(DME) systems in the 1025- to
1150-MHz range. The HVV1012-060,
HVV1012-100, and HVV1012-250 are
designed for use with pulsed L-band signals.
All three have been characterized
with a +48-V dc supply and with 10-µs
pulse-width signals at 1% duty cycle.
In spite of the novel architecture, these
L-band power transistors are based on
conventional silicon substrate materials,
typically relying on multiple transistor
cells in a push-pull configuration to
achieve high output-power levels. Some
transistor suppliers, such as Microsemi,
have sought out more exotic device materials
for higher transistor power, including
silicon carbide (SiC) with its outstanding
thermal properties, to dissipate the heat
generated by the active device cells.
Microsemi’s 0150SC-1250M and
0405SC-1000M RF power transistors
are SiC-based static-induction transistors
(SITs), single-ended designs with very
simple impedance-matching requirements
compared to typical silicon bipolar
or LDMOS transistors. The Class
AB transistors are about half the size of
equivalent-power LDMOS or bipolar
transistors.
The 0150SC-1250M typically provides
1400-W pulsed output power in the
very high-frequency (VHF) band from
150 to 160 MHz. The 0405SC-1000M
typically delivers 1100-W pulsed output
power in the ultra-high-frequency
(UHF) band from 406 to 450 MHz.
The SiC transistors are housed in single-
ended flange-mount power packages,
assembled with 100% gold metallization
and gold wire bonds in hermetic packages
for the highest reliability in hostile environments.
They are ideal for solid-state
power amplifiers for VHF weather radar
and long-range tracking radar systems.
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