Sunnyvale, CA company Spectrian (former MMD - Microwave Modules and
Devices in the 1980s) has spun off their semiconductor manufacturing
into UltraRF. Spectrian supples RF power modules to the wireless
market, for base stations, etc.
Because of the long history of building high power RF modules, and
that some of the engineering people have learned from CTC and Acrian,
this company has some very nice technology to offer for high power
solid state amplifiers. Mostly higher frequency stuff than HF range.
[BACKGROUND
CTC (Communication Transistor Corp, long out of business) wrote the
book on building bipolar RF amplifiers, and the application note
SOLID CIRCUITS (1973) by Joe Johnson, Lee Max, Bob Artigo, and
others is still a classic for the design of bipolar power amplifiers
(much as Pappenfuss et al is for SSB amplifiers). A series of QST
articles by Johnson/Artigo at that time also covered some of the same
techniques, when solid state power amps for VHF were in their
infancy. ]
UltraRF's online application notes are excellent, see:
http://www.ultrarf.com/html/application_notes.htm
They printed this comparison of technologies, for amplifiers-
Advantage of LDMOS Devices for High Power RF Stages
-Higher gain than equivalent bipolar
devices (common lead inductance)
-Can have all terminals isolated for IC process
-More rugged, will withstand greater load
mismatch abuse
-Superior linearity at medium and lower
power levels
- Potentially higher efficiency when
backed down for linearity
-Single supply vs dual for GaAs
-Lower cost of manufacture due to low
cost (non-BeO/AlN) package
-Easier to broadband due to greater input
mismatch tolerance
-Can be fabricated in a CMOS fab process
-Current market "favorite"
Advantages of Bipolar Devices for High Power RF Stages
-Highest power density
-Lowest output capacitance (easier to
broadband with good efficiency)
-Simple circuit with no bias circuit for
CW applications
-Higher peak power capability under pulse
application
-High voltage process available
-No inherent bias drift
-No inherent drain resistance drift
-No time dependent dielectric failure mode
73
K5PRO
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