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Envelope Amplifier for ERR and ET Architectures
using RF Si-LDMOS Technology
M. Patiño
The Envelope Elimination and Restoration (EER) and Envelope Tracking (ET) are
topologies that increase the efficiency of the RF power amplifiers. A cornerstone
in this system is the envelope amplifier because high dynamic range and high
efficiency are required at the same time. Here we propose a solution based on a
high switching frequency two phases buck converter using RF Si-LDMOS
transistors to obtain very fast switching times.
Grupo de
Ingeniería de Radio
Project sponsored by
ENVELOPE AMPLIFIER DESIGN
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Two phases asynchronous buck converter. Easy open loop
PWM control.
High switching frequency (15 MHz) due to RF LDMOS (high
slew rate) transistors and low parasitic capacitance
schottky diodes.
Fourth order Chebyshev low pass filter (5.8 MHz cut-off
frequency).
High efficiency VHF (88 – 108 MHz) Class-E power amplifier
(Load).
Switching stage
Low pass filter
Load
EER TOPOLOGY PROTOTYPE (ENVELOPE AMPLIFIER + CLASS-E RF POWER AMPLIFIER)
Power measurements (OFDM):
 Supply voltage: 28 V
 Output peak power: 150 W
 Drain efficiency: 71 %
 Power added efficiency : 62%
RF input
signal
from
driver
Envelope amplified signal measured
waveform. Noise is due to the RF
amplifier. It does not affect the overall
system linearity.
Modulated OFDM output amplified
signal measured waveform (1.5 MHz
bandwidth).
Creating OFDM envelope
test signal with MATLAB
Source LDMOS waveform. 15 MHz
switching frequency. Spikes are due to
MOSFET parasitic package effects.
Control
injection
2φ PWM Modulator
CONCLUSIONS
An envelope amplifier for EER and ET techniques is presented here. The prototype has been tested with a Class-E RF power amplifier
employing an EER topology, obtaining a drain efficiency of 71% over a 1.5 MHz RF (5 MHz envelope) bandwidth OFDM test signal. This
converter is suitable for ET topologies (up to several megahertz bandwidth) and EER systems up to 1.5 MHz RF bandwidth. Also it is possible
to combine it with a linear amplifier to obtain a higher bandwidth.
Centro de Electrónica Industrial (CEI) | Universidad Politécnica de Madrid | [email protected] | www.cei.upm.es