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here to go to our main page on nonlinear devices
here to go to our page on compression point
here to go to our main page on MMIC design
to go to our main page on FETs
to go to our main page on HBTs
to go to our main page on microwave tubes
What is more fun than a microwave
amplifier? Nothing. Everything in the natural universe spells loss
for your microwave signal, that is the consequence of entropy. Only
the sheer genius of an amplifier designer boosts your signal back
from the abyss!
While we're building up more
content on amplifier design, here's a good link to Queen's
University web site that has a lot of information on the topic.
Thanks to Sibasis!
Fellow microwave Dudes, we sure
could use some pictures to go along with this text! Send us a picture
and you'll receive a cool Microwaves101
pocketknife! Don't make us draw stuff with Microsoft Word, that
gets ugly for everyone.
Below is an index to all of our
material on amplifiers. In expanding our discussion on amplifiers,
first we had to break it into several separate pages so it won't
become a pain to load.
amplifiers (new for February 2009)
(new for February 2009)
amplifiers a.k.a. traveling-wave amplifiers
directivity of amplifiers
amplifiers (new for July 2008!)
classes (new for July 2008!)
Below are some leftover amplifier
topics that we haven't written about yet. Want to help us write
about any of these topic, for fame or fortune? Contact
A push-pull amplifier uses two
amplifier stages in parallel. The input to the devices is 180 degrees
out of phase. The FETs are biased in Class
B, where they conduct in alternating cycles.
A complimentary amplifier uses
opposite polarity (PNP and NPN) transistors to operate class B yet
still provide the waveform. There is distortion, because both of
the transistors have threshold voltages to overcome. In an HBT implementation,
biasing the base at 0.6 volts can reduce this form of distortion.
Microwave amplifiers can provide
ten's of GHz of bandwidth, even operate down to DC!
to go to our main page on microwave tubes.
Gain block amplifiers
A gain block is usually not a
great power amp and not a great low-noise amp, but a pretty good
wideband amp. Gain blocks are convenient, the designer merely drops
them in where gain is required, so long as the application can afford
the noise figure and low efficiency.
Feed-forward amps are used to
reduce distortion such as second intermodulation products.
versus continuous wave (CW) amplifiers
By pulsed amplifier we mean one
that is electrically switched off when it is not amplifying. Most
CW amplifiers can be used as pulsed amplifiers, but not all pulsed
amplifiers can be used CW.
Pulsing the amplifier on/off
reduces DC power dissipation, which means that it operates at a
cooler temperature. In some cases operating a pulsed amplifier continuously
will cause damage due to heat.
They length of the pulse has
an effect on how hot the pulsed amp will get, if it is long compared
to the thermal time constant.
Because pulsed amplifiers run
cooler, they often can provide higher power and efficiency compared
to similar CW amplifiers.
Pulsed amplifiers require special
power supplies to maintain the DC bias point during the pulse; often
large charge storage capacitors are needed.
For very short pulses, you need
to consider the bandwidth of the amplifier, so that it maintains
the pulse shape.