[AMPS] UltraRF

[John T. M. Lyles]

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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