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ce
i@u
pm
.es
Universidad Politécnica de Madrid
High Efficiency Power Amplifier based on Enevelope Elimination
and Restoration
Miroslav Vasić
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Tercer Seminario Anual CEI
Mayo 2010
Spectral Efficiency
▪ Due to tremendous growth of data transmission, the need for high spectral efficiency has increased as well
D.Brubaker, “Optimizing Performance and Efficiency of PAs in Wireless Base Stations: Digital pre-distortionreduces signal distortion at high power levels”, White Paper, Texas Instruments, February 2008
▪ The main task of modern modulation techniques is to transmit as much data as possible per unit of spectrum in an economical way
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Tercer Seminario Anual CEI
Mayo 2010
Need for linear Power Amplifiers (PA)
▪ In order to increase spectral efficiency complex modulationschemes based on multi-carriers are employed (e.g. OFDM)
▪ The transition to spectrally efficient wireless standards has dramatically increased the cost to deploy and operate wireless services
▪ Modulations that employ multi-carriers lead to the signal that hasnon-constant envelope. Therefore, the linearity of Power Amplifiers(PA) rises as one of the primary concerns in moderntelecommunication applications
▪ Due to the need for linearity, linear PA (class A, B or AB) are used. Unfortunately, these PA suffer from very low power efficiency
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Tercer Seminario Anual CEI
Mayo 2010
The root of the problem
This is for a sinewave signal !!!
We would like to transmita signal with variable envelope
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Mayo 2010
Why do we need high efficiency?
Cheaper equipment
Decreased energy and service cost
Benefits of higher efficiency
Reduction of air coolers and heat sinks (more space)
Reduced CO2 footprint, less pollution
▪ Our objective is to enhance the efficiency of Power Amplifiers (PA)
▪ In this project we have collaborated with another research group: GIRA -UPM
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Tercer Seminario Anual CEI
Mayo 2010
Kahn’s technique
▪ Linearization of a non linear PA
▪ The basic idea is to apply simulataneous envelope and phase modulation to a non linear PA
Envelope Modulation
Phase modulation
▪ Envelope Elimination and Restoration (EER)
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Tercer Seminario Anual CEI
Mayo 2010
Power Amplifier based on EER
The envelope amplifier has to provide High linearity High efficiency Wide bandwidth Minimum interfierence with the spectrum of the output signal
The non linear (class E) PA has to guarantee High efficiency
Low AM-AM and AM-PM conversions(parasitic conversions that low the transmitters linearity)
Good synchronization between the envelope and phase modulationin order to obtain high linearity of the EER based PA
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Tercer Seminario Anual CEI
Mayo 2010
Proposed Envelope Amplifier
Multilevel Converter
VOVA
Control
Control
VIN
VR
Linear Regulator
time
Vol
tage Vin linear regulator
1
2
n
st cell
nd
th
cell
cell
time
Volta
ge
Vin linear regulator
Venvelope
(Vmultilevel)
n cellth
2nd cell
1st cell
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Tercer Seminario Anual CEI
Mayo 2010
Implementation of the multilevel converter
Vinput
Multioutput C
onverter
Vin
Vin
1
n
n-1
Vin
Vc
Vc
c
A
Cell
Cell
Cell
Nº n
Nº 1
Nº (n-1)
Trigger n
Trigger (n-1)multilevelV
B
Trigger 1
V 1
n-1
n
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Tercer Seminario Anual CEI
Mayo 2010
M.Vasiċ, O.Garcia O, J.A.Oliver, P.Alou, D.Diaz, J.A.Cobos, “Switching Capacities based Envelope Amplifier for High Efficiency RF Amplifiers”, 25th Annual IEEE Applied Power Electronics Conference, APEC2010, Palm Springs, USA, February 2010.
D.Diaz, M.Vasić, O.Garcia, J.A.Oliver, P.Alou, J.A.Cobos, “Comparison of two different cell topologies for a multilevel power supply to achieve high efficiency envelope amplifier”, Proc. of the IEEE Energy Conversion Congress and Exposition, ECCE2009, September 2009
Envelope amplifier prototypes
1
2
M.Vasić, O.Garcia, J.A.Oliver, P.Alou, D.Diaz, J.A.Cobos, “Multilevel Power Supply for High Efficiency RF Amplifier”, Proc. of the 24th Annual IEEE Applied Power Electronics Conference, APEC2009, February 2009
Good propertiesHigh bandwidth of the envelope amplifier: 2 MHz
Peak power: 50W
Efficiency: 40% - 70%
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Tercer Seminario Anual CEI
Mayo 2010
The optimization is necessary ! !
▪ In order to obtain high linearity of the multilevel converter it is necessary to optimize the number of levels and its distribution
▪ Equidistant voltage distribution is not the optimal one!
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Tercer Seminario Anual CEI
Mayo 2010
Prototype of the PA based on EER
Specifications for the envelope amplifier
Input voltage: 24V
The first stage is a flyback converter (fsw=50kHz) with 3 outputs
Two 6 V levels and one 12 V level
The multilevel converter is composed of two-level voltage cells
Variable envelope from 0 V to 23 V
Peak power: 100W
Bandwidth of the envelope amplifier: 2MHz
Envelope amplifier
Class E Power Amplifer Designed and implemented by GIRA - UPM It operate at VHF (between 95 MHz and 125 MHz) Depending on the carrier frequency, the efficiency can vary between 75% y 90%
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Tercer Seminario Anual CEI
Mayo 2010
EER amplifier
FPGA, D/A and A/Dconverters
Class EAmplifier
EnvelopeAmplifier
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Tercer Seminario Anual CEI
Mayo 2010
The first test – simple AM modulation
▪ The envelope is a 2 MHz sine wave
Envelope
Multilevel
RF
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Tercer Seminario Anual CEI
Mayo 2010
The first test – simple AM modulation
The envelope is composed of two tones
Envelope
Envelope reference
Multilevel
RF
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Tercer Seminario Anual CEI
Mayo 2010
Measurements of linearity
The linearity is measured using two tone test
The synchronization of the enevelope and phase modulation is of crucial importance for high linearity
In order to boost the system’s linearity the predistortion technique is applied
Attenuation of the intermodulationproducts is 22 dB without predistortion
Attenuation of the intermodulationproducts is 44 dB with predistortion
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Tercer Seminario Anual CEI
Mayo 2010
Efficiency Measurements
The system has been tested with QAM64 signal
Time domain
The constellation and the spectrum of the output signal
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Tercer Seminario Anual CEI
Mayo 2010
Efficiency Measurements
The system has been tested with QAM64 signal
The implemented PA has up to 35% less of power losses than an ideal conventional (linear) solution!
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Tercer Seminario Anual CEI
Mayo 2010
Conclusions
▪ We have presented a solution for a PA based on Kahn’s technique (EER)
▪ The envelope amplifier has the bandwidth of 2 MHz and can provide up to 100 W of instantaneous power
▪ The attenuaiton of the intermodulation products is higher than 40 dB
The implemented PA has up to 35% less of power losses than an ideal conventional (linear) solution!
