Hi Paul..
Check out US Patent 4588958 by Allen Katz K2UYH. It's a common way to linearize
solid state PAs for the cellular market back in the day. The basic idea is to
emulate the compression curve of the amplifier (gain rolloff as power input
increases) using the nonlinearity of a diode. The trick Al discovered is how to
use a 90 deg hybrid to reflect the nonlinearity back into the input path in a
useful way. I don't know if that's what AC2IQ uses. He definitely has some
cool ideas.
Another good source on the description of the causes of linearity and the
requirement on linearization comes from Joel Vuolevi's PhD thesis
"Analysis, measurement and cancellation of the bandwidth and amplitude
dependence of intermodulation distortion in RF power amplifiers"
and later book
"Distortion in RF Power Amplifiers"
I learned a tremendous amount from studying the Katz and Vuolevi work when I
worked on high linearity cellular systems.
Amateurs should really to attack the splatter problem. Most of the interference
on the bands comes from splatter from many -30 dBm IMD transmitter and
amplifiers. It's easy to get 10 dB improvement in IMD with a pre-distort
linearizer. Getting up to 30 dB is feasible but takes a digital system and
complex design.
Many high power, high efficiency, low IMD cellular amplifiers use a Doherty
circuit with one amplifier handling the low level parts of the signal and
another handling peaks.
jeff, wa1hco
On 05/03/2013 08:18 AM, Paul Christensen wrote:
Not exactly Motorola transistor related but the subject reminded me of this:
AC2IQ has developed an interesting pre-distortion "linearizer."
http://www.qrz.com/db/AC2IQ
Linearizers have been used in the cell phone industry to more efficiently pack
more digitally-modulated channels into licensed spectrum. Broadcasters have
been using this technology for the last decade. Swiss ADAT was the first
amateur manufacturer to use the technology in their ADT-200A transceiver. In
fact, it works so well that within limits, the ADAT will sample the output of
a non-linear amp, and correct for the amp's non-linearity back in the
transceiver.
Apparently, AC2IQ is using an analog, rather than a digital method to achieve
extreme linearity from his SD2931x16 MOSFET amp. Not sure what class the amp
is biased. Scroll down to the middle of the page and you can see the result
of his work. This isn't just lab performance. Folks have observed his 75m
signal with no IMD "wings" on their SDR receivers.
I'm aware of digital adaptive pre-distortion techniques, but I've not seen
this done using analog components. Anyone familiar with this type of circuit?
Paul, W9AC
----- Original Message ----- From: "Paul" <w8aef@q.com>
To: "Amps" <amps@contesting.com>
Sent: Tuesday, April 30, 2013 7:12 PM
Subject: [Amps] Motorola transistors
From: Paul
Sent: Tuesday, April 30, 2013 4:11 PM
To: ScQRPions
Subject: Motorola transistors
Advanced Semiconductor continues to make most Motorola, Philips, and SGS
Thompson RF transistors.
http://www.advancedsemiconductor.com/index.html
de Paul, W8AEF
ZF2JI/ZF2TA 8Q7AA FO8DX/FO0PLA XZ0A VU7RG/VU3PYM TX5A A52PP
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