NEWCOM WPR3 Meeting – Uppsala 21 09 05 RF & Microwave Electronics Group

Power Amplifier for Wireless Links:System Level Models

Daniel BustosMarco PirolaGiovanni GhioneSimona Donati

Dipartimento di ElettronicaPolitecnico di TorinoMicrowave & RF Electronics Group

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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;

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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-> 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.

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Envelope or base-band model II

N L

dev ice /c ircu it

R F M O D B B D E M O D

H ig h -L ev e l (E n v e lo p e ) S y s tem M o d e l

ou

in

tput ( ) Re ( )exp( ) ( ) cos (

put ( ) Re ( )

)

exp( ) ( ) cos ( )

c c

c c

y t y

x t x t j t x t t x t

t j t y t t y t

x(t) y(t)

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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 -> 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

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Circuit Level – System Level Link

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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;

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

The implemented models

U(k)

Linear Part with Memory

AM -AM

AM - PM

Static Nonlinear Part

W(k) y(k)

AM -AM

AM - PM

Static Nonlinear Part

y(k)U(k)

Classical AM-AM, AM-PM

Advanced Wiener Scheme Model

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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)

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

SUBCKTID=S1NET="AmpF"

SUBCKTID=S2NET="AmpF"

PORTP=2Z=50 Ohm

PORT_PS1P=1Z=50 OhmPStart=-10 dBmPStop=20 dBmPStep=0.5 dB

RESID=R1R=47 Ohm

CAPID=C3C=1e4 pF

RESID=R3R=1000 Ohm

RESID=R2R=1000 Ohm

CAPID=C4C=1e4 pF

CAPID=C7C=1e4 pF

RESID=R5R=4 Ohm

DCVSID=V2V=3.3 V

INDID=L1L=3.9 nH

INDID=L2L=3.9 nH

DCVSID=V1V=1.2 V

INDID=LL1L=LL nH

SUBCKTID=S4NET="R07S5R6_SER"

SUBCKTID=S5NET="R07S5R6_SER"

SUBCKTID=S2NET="R07S0R8_SER"

SUBCKTID=S3NET="R07S2R2_SER"

1

2

3

SUBCKTID=S6NET="curtice2"

PORTP=2Z=50 Ohm

PORTP=1Z=50 Ohm

MWO Diagram of Driver Amplifier

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Example: WLAN 802.11a Driver AmplifierSingle Tone AM/AM at 5 GHz

Input Power, dBm

Ou t

put P

ower

, dBm

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Single Tone AM/PM at 5 GHz

Input Power, dBm

Out

put P

hase

, deg

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Two-tone simulation at 0 dBm input power

Left Tone Output Power

22

23

24

25

26

27

28

29

0.01 0.05 0.07 0.1 0.2 0.3 0.4 0.5 1

Tone Spacing, GHz

Powe

r, m

W

VSS MODEL IT++ MEMORY MODEL MWO REFERENCE

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Right Tone Output Power

0

5

10

15

20

25

30

0.01 0.05 0.07 0.10 0.20 0.30 0.40 0.50 1.00

Tone Spacing, GHz

Powe

r, m

W

VSS Model IT++ Memory Model MWO Reference

Two-tone simulation at 0 dBm input power

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

Two-tone simulation at 0 dBm input power

IM3 Left Line

0

2

4

6

8

10

0.01 0.05 0.07 0.1 0.2 0.3 0.4 0.5 1

Tone Spacing, GHz

Powe

r, m

icroW

VSS MODEL IT++ MEMORY MODEL MWO REFERENCE

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

IM3 Right Line

0

2

4

6

8

10

0.01 0.05 0.07 0.1 0.2 0.3 0.4 0.5 1Tone Spacing, GHz

powe

r micr

oW

VSS MODEL IT++ MEMORY MODEL MWO REFERENCE

Two-tone simulation at 0 dBm input power

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

OFDM Mod. scheme: BER simulation at several PA compression levels

0 5 10 15 20 25 30

10-4

10-3

10-2

10-1

100

EB

/N0

BE

R

IDEAL PA

Ibo=8 dB

Ibo=6 dB

Ibo=4 dB

Ibo=0 dB

, dB

RF & Microwave Electronics GroupNEWCOM WPR3 Meeting – Uppsala 21 09 05

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, …)