Speaker
Amreen Khan
Title
High Efficiency Two-Stage GaN Power Amplifier with Improved Linearity
Abstract
The
tradeoff
between
linearity
and
efficiency
is
the
limiting
point
wideband
power
amplifier
design.
The
wireless
research
focuses
a
lot
its
effort
on
building
power
amplifiers
with
these
two
criteria
going
hand
in
hand
to
build
an
optimal
design.
This
thesis
investigates
the
various
sources
of
nonlinearity
associated
with
GaN
HEMT
transistors
and
their
effects
on
the
linearity
metrics
of
power
amplifiers.
The
investigation
is
based
on
the
analysis
of
these
sources
of
nonlinearity,
a
design
based
approach
to
mitigate
them
and
compare
to
existing
trends
in
power
amplifier
design.
The
device
technology
used
in
this
design
is
CREE
GaN
HEMT
transistors
(45W
and
6W).
In
this
report,
a
systematic
approach
to
designing
a
two
stage
power
amplifier
is
discussed
and
analyzed
for
design
of
linear
and
highly
efficient
power
amplifier
for
base
stations.
The
power
amplifier
consists
of
two
stages,
the
driver
stage
and
the
power
stage.
The
driver
stage
aims
to
linearize
the
power
stage
using
circuit
analysis
and
transistor
properties
along
with
providing
the
necessary
gain.
The
power
stage
is
built
to
compliment
the
driver
stage
and
to
achieve
high
efficiency
of
the
power
amplifier.
The
inter-stage
matching
network
between
the
two
stages
achieves
the
required
matching
of
impedances
and
the
transmission
lines
in
the
bias
feed
control
the
harmonic
impedances
for
optimal
performance
without
disrupting
performance
at
fundamental
frequencies.
This
effectively
improves
and
maintains
high
efficiency
over
200MHz
of
bandwidth.
The
design
approach
is
simulated
and
fabricated
to
test
the
feasibility
of
a
linear
power
amplifier
operation
with
the
use
of
DPD.
The
fabricated
prototype
achieves
about
70%
peak
efficiency
over
the
bandwidth
and
maintains
linearity
of
above
40dBc
ACLR
and
below
3%
EVM.
The
measurement
results
indicated
that
the
need
for
DPD
is
eliminated
back-off
at
the
center
frequency
(800MHz).
The
thesis
presents
a
detailed
comparison
of
the
prototyped
design
with
the
existing
multistage
designs
with
linear
driver.
The
report
completes
with
conclusions
drawn
from
measurements
and
the
bandwidth
limitations
faced
through
the
course
of
the
design.
Lastly,
the
possible
future
work
is
discussed
that
may
allow
to
overcome
the
limitations
of
the
design.
Supervisor
Professor Slim Boumaiza