Power Amplifier for Wireless Links: System Level Models

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Power Amplifier for Wireless LinksSystem Level
Models

• Daniel Bustos
• Marco Pirola
• Giovanni Ghione
• Simona Donati
• Dipartimento di Elettronica
• Politecnico di Torino
• Microwave RF Electronics Group

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Outline

• Behavioral nonlinear model motivations
• The implemented models
• The cooperation between Polito and Chalmers
  Units
• Simulatotion Tools
• Model and extraction procedure description
• Some simulation examples (IM3, BER, )
• A case study a 812.11a WLAN Power amplifier
• Model the PHEMT ATF-54143 Transistor
• Circuit level and system level simulations
• Model behaviour comparison (VSS VS IT)
• Conclusions and future works

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Envelope or base-band model I

• Oriented to high level (system) simulations (eye
  diagram, BER) rather than circuit ones
• Identified through input/output system
  observation-gt intrinsically behavioural
  (black-box)
• System level modelling is oriented to the
  prediction of the system envelope behaviour
• System evaluation through RF simulation possible
  but
• simulation circuit level far from the system
  level layer
• system level model identification directly
  focused on system
• system level simulation unbearably slow.

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Envelope or base-band model II
x(t)
y(t)
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Motivations I

• The models used to simulate the PA at circuit
  level are capable to represent nonlinearities
  with a high degree of accuracy
• Memory effects in principle included, although
  difficulties are related to the model extraction
  (from measured data or physics-based simulations)
  and to the simulation techniques used (HB)
• System level simulation unsuitable for fast
  simulation in presence of complex modulation
  scheme-
• Classical system level models include
  nonlinearities in a too simplistic way -gt lost of
  accuracy for complex modulation schemes
• More sofisticated models
• need complex identification procedures
• increase the computation time

Find a model trade off between accuracy, simple
model parameter identification, reasonable
computation time
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Motivation II

• Chalmers unit develops and maintains a system
  level simulator (IT) adopted within the NEWCOM
  network
• IT is able to implement a complete
  communication links at system level
• IT did not account for the effects of PA non
  idealities on the system level performances
• Polito units has a consolidated activities on the
  PA field at circuit and system level (e.g.
  activities within TARGET network).

Implement within IT the Polito NL models
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Circuit Level System Level Link
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Simulation framework

• Circuit level simulations carried out with AWR
  MWOFFICE, used as the reference model virtual
• System level identification through practicable
  non-linear experimental data
• Automated extraction implemented at the moment
  within Matlab
• System level simulation
• AWR VSS automatically extracted from MWO
• Classical AM-AM AM-PM model implemented in IT
• Advanced model with memory implemented in IT
• Comparisons on a case study power amplifier for
  WLAN 802.11a application

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The implemented models
Classical AM-AM, AM-PM
y(k)
U(k)
Static Nonlinear Part
Advanced Wiener Scheme Model
U(k)
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Memory Model Extraction

• The linear part of the model extracted from two
  tone excitation varying the tone spacing
• FIR filter implemented through ARX approach
• Static nonlinear part, extracted for single and
  two tones excitation as a function of tone power
• Non linear static behaviour approximated with a
  suitable degree polynomial

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Case of study A 802.11a WLAN Driver Amplifier
using PHEMT ATF-54143 Transistor

• The frequency range includes USA U-NII lower band
  5.125 5.250 GHz.
• MWO tools used to simulate a circuit
  implementation.
• For the nonlinear analysis, a harmonic balanced
  (HB) simulation was used
• The Non-linear transistor model used in the
  simulation is based on the work of Curtice
  (Advanced Curtice2 Model)

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MWO Diagram of Driver Amplifier
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Example WLAN 802.11a Driver Amplifier
Single Tone AM/AM at 5 GHz
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Single Tone AM/PM at 5 GHz
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Two-tone simulation at 0 dBm input power
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Two-tone simulation at 0 dBm input power
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Two-tone simulation at 0 dBm input power
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Two-tone simulation at 0 dBm input power
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OFDM Mod. scheme BER simulation at several PA
compression levels
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Conclusions

• Collaboration with Chalmers Univeristy through
  PhD student exchange (maybe to be renewed)
• Methodology for extraction of system oriented
  models from measured data or standard HB
  (multitone) circuit simulations
• Model validation on virtual experimental data
• Extractor implemented in Matlab
• Model implemented within IT
• Future possible developments
• model validation on true experimental non linear
  data
• further model refinements and improvements (e.g.
  three box model)
• testing and implementation of other models (e.g.
  neural, volterra/wiener series appproach, )