predicting total harmonic distortion (thd) in adsl ... · adsl transformer design issues the adsl...

Peter R. Wilson

Electronic Systems Design Group

University of Southampton, UKSchool of Electronics and Computer ScienceDr Peter R. Wilson – BMAS 2003

1

Predicting Total Harmonic Distortion (THD)Predicting Total Harmonic Distortion (THD)in ADSL Transformers using in ADSL Transformers using BehaviouralBehavioural ModelingModeling

Peter R. Wilson, J. Neil Ross & Andrew D. BrownPeter R. Wilson, J. Neil Ross & Andrew D. BrownSchool of Electronics and Computer ScienceSchool of Electronics and Computer Science

University of Southampton, University of Southampton, UKUK

Peter R. Wilson



2

OutlineOutlineIntroductionIntroduction

• ADSL• Where is the need for the transformer?• What are the design Issues?

ModelingModeling and Simulationand Simulation• Basic Transformer modeling• Non-linear modeling• System modeling

Hardware modificationsHardware modifications• Planar transformers

ConclusionsConclusions

Peter R. Wilson



3

ADSL: IntroductionADSL: IntroductionAAsymmetric symmetric DDigital igital SSubscriber ubscriber LLine ine

• The technology is used as a high-speed modem link with asymmetric up- and down-stream data rates

• The technology is important because it uses the existing standard POTS network infrastructure

• The mechanism only requires an ADSL modem at the local telephone exchange (CO) and a similar modem at the customer site (CP)

ATU-CDigitalBroadcastBroadbandNetwork

NarrowbandNetworkNetwork

Management

ATU-C

ATU-C

ATU-C

ATU-C

PSIN Phones

ATU-RTETETETE

Central Office Customer Premises

Loop

Splitter

ADSL Termination Unit –Central (ATU-C)

ADSL Termination Unit-Remote (ATU-R)

Peter R. Wilson



4

ADSL Modulation SchemeADSL Modulation SchemeADSL is based on a broadband modulation scheme ADSL is based on a broadband modulation scheme

• multiple carriers placed at 4.3125kHz intervals• With 256 carriers a 1.1MHz bandwidth is required• These sub-carriers may also be referred to as sub-channels.

ADSL coADSL co--exists with POTSexists with POTS

POTS

Ups

tream Downstream

frequency

4kHz 25kHz 160kHz 240kHz ~1.1MHz

Peter R. Wilson



5

ADSL ADSL AnalogAnalog InterfaceInterfaceThe signals are transmitted using a form of QAM, eitherThe signals are transmitted using a form of QAM, either

• Carrier-less Amplitude/Phase Modulation (CAP)• Quadrature Amplitude Modulation (QAM)

The modulators and demodulators are interfaced to the line The modulators and demodulators are interfaced to the line with:with:

• Channel splitting filters• Impedance-matching wide-band transformers

HighPassFilter

ADSLChipset

WidebandTransformer

HighPassFilter

LowPassFilter

ADSLChipset

WidebandTransformer

LowPassFilter

ISP

PSTN

PC

Phone

Central Office Modem Home Modem

TwistedPair

<6 Mbps

Peter R. Wilson



6

ADSL transformer design issuesADSL transformer design issuesThe ADSL transformers have several basic requirements:The ADSL transformers have several basic requirements:

1.1. Wide BandwidthWide Bandwidth1. This implies low loss, low leakage and low capacitance

2.2. Low Insertion LossLow Insertion Loss1. This implies low resistance and loss

3.3. Low DistortionLow Distortion1. This implies good linearity

4.4. Compact SizeCompact Size1. There is a design trade-off between distortion and size

Peter R. Wilson



7

ModelingModeling Insertion LossInsertion LossWe can use a simple linear model, with accurate We can use a simple linear model, with accurate parasiticsparasitics to to predict the insertion loss over a wide frequency rangepredict the insertion loss over a wide frequency rangeThis is well understood and works reasonably wellThis is well understood and works reasonably well

LLp

10uH

Rp

0.5

Cp50p

Ciw

50p

TX1Rs

0.5

LLs

10uH

Cs50p

-50

-40

-30

-20

-10

0

10

1000 10000 100000 1000000 10000000

Frequency (Hz)

Inse

rtio

n Lo

ss (d

B)

Peter R. Wilson



8

Predicting DistortionPredicting DistortionDistortion is a result of nonDistortion is a result of non--linearitieslinearities in the transformerin the transformerThe source of the nonThe source of the non--linearitieslinearities is mainly from the ferrite is mainly from the ferrite core of the transformercore of the transformerDistortion is quantified for ADSL system designers using the Distortion is quantified for ADSL system designers using the Total Harmonic Distortion Measure (THD), which is closely Total Harmonic Distortion Measure (THD), which is closely related to the Signal to Noise Ratio (1/THD)related to the Signal to Noise Ratio (1/THD)THD in this context is usually calculated using:THD in this context is usually calculated using:

1

5

2V

V

THD ii∑

==

Where:Vi is the harmonic (i)V1 is the fundamental

Peter R. Wilson



9

Ferrite Material Ferrite Material HysteresisHysteresisFerrite materials exhibit some form Ferrite materials exhibit some form of of hysteresishysteresis

• The trouble with signal transformers is that a convenient major loop cannot be assumed

• The loops may be:• Assymetric• Minor

• Modeling these effects is actually very difficult to accomplish accurately, as the standard models assume a major loop

B

H

Major Loop

InitialMagnetization

AsymmetricMinorLoop Symmetric

MinorLoop

Peter R. Wilson



10

Different Loop Types Different Loop Types –– Small Minor LoopSmall Minor LoopLinearLinearNo LossesNo LossesMinimal DistortionMinimal Distortion

-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

-1.5 -1 -0.5 0 0.5 1 1.5

H (A/m)

B (T

)

Peter R. Wilson



11

Different Loop Types Different Loop Types –– Medium LoopMedium LoopSmall Small HysteresisHysteresisLow LossesLow LossesMinimal DistortionMinimal Distortion

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

-15 -10 -5 0 5 10 15

H (A/m)

B (T

)

Peter R. Wilson



12

Different Loop Types Different Loop Types –– Major Loop #1Major Loop #1Significant Significant HysteresisHysteresisSignificant lossesSignificant lossesLarge DistortionLarge Distortion

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

-60 -40 -20 0 20 40 60

H (A/m)

B (T

)

Peter R. Wilson



13

Different Loop Types Different Loop Types –– Major Loop #2Major Loop #2Significant Significant HysteresisHysteresis

• Slightly reducedSignificant lossesSignificant losses

• Relatively smallerLarge DistortionLarge DistortionEarly ClosureEarly Closure

-0.40

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.40

-60.00 -40.00 -20.00 0.00 20.00 40.00 60.00

H (At/m)

B (T)

Peter R. Wilson



14

MixedMixed--Domain ModelDomain ModelThe approach used in this paper was to use a mixedThe approach used in this paper was to use a mixed--domain domain model of the transformer, with a modified Jilesmodel of the transformer, with a modified Jiles--Atherton core Atherton core modelmodel

• Single Lumped Model

R1

50

U1

MMF

winding

R4

U6

classicja

U2

MMF

winding

V1R2100

vs vp vout

Peter R. Wilson



15

Handling Minor LoopsHandling Minor LoopsThere are three approaches to dealing with minor loopsThere are three approaches to dealing with minor loops

1.1. Characterise the model over a wide range of operationCharacterise the model over a wide range of operation1. This is OK, but means accuracy is compromised for each specific

case, in favour of a generally accurate model2.2. Characterise for only minor loopsCharacterise for only minor loops

1. This works well, but is very specific3.3. Modify the model to change behaviour for minor loopsModify the model to change behaviour for minor loops

1. In theory this sounds good, but the existing models do not implement this capability. Plus, the models need a-priori knowledge of turning points, which leads to innacuraccies.

Peter R. Wilson



16

Characterisation SoftwareCharacterisation SoftwareTo handle multiple loop optimisation, software has been To handle multiple loop optimisation, software has been developed to take measured BH curve data and extract developed to take measured BH curve data and extract parameters that best fit all the curves imported from different parameters that best fit all the curves imported from different signal levelssignal levels

Peter R. Wilson



17

Characterised WaveformsCharacterised WaveformsThree Measured LoopsThree Measured Loops

• Major• Medium• Minor

Optimiser SettingsOptimiser Settings• 3 loop fit• Equal weighting• Genetic algorithm

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

-150 -100 -50 0 50 100 150

H(A/m)

B(T

)

Peter R. Wilson



18

Modifications to the JilesModifications to the Jiles--Atherton ModelAtherton ModelModifications were also made to the original JilesModifications were also made to the original Jiles--Atherton Atherton magnetic model to improve the minor loop magnetic model to improve the minor loop modelingmodeling, , basically modifying the behaviour depending on the recent basically modifying the behaviour depending on the recent turning pointsturning points

• Worked well statically• Less effective dynamically• Poor with arbitrary waveforms• Relies on turning points

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

-40 -20 0 20 40

H (A/m)

B (T

)

Modified JA Model Measured Original JA Model

Peter R. Wilson



19

Predicting the THD of ADSL transformersPredicting the THD of ADSL transformersIn practice, there was no need to have overly sophisticated In practice, there was no need to have overly sophisticated models to predict the performance of the transformer as an models to predict the performance of the transformer as an individual component, as the standard tests were undertaken individual component, as the standard tests were undertaken at single frequencies at a time.at single frequencies at a time.Models were created for standard core types and materials, Models were created for standard core types and materials, simulated and the resulting THD compared with measured simulated and the resulting THD compared with measured results using the same componentsresults using the same components

• Toroid TN10/6/4-3E5• Low Profile E11R-3E6• Integrated Inductive Component IIC• Custom planar Devices E18/E14• EP Cores (standard wire-wound) EP13

Peter R. Wilson



20

ToroidToroid TN10/6/4TN10/6/4--3E53E5

-70

-60

-50

-40

-30

-20

-10

0

0 2 4 6 8 10 12

Peak Voltage (V)

TH

D (d

B)

Measured Simulated

Peter R. Wilson



21

ER11ER11--3E63E6

-50

-40

-30

-20

-10

0

0 2 4 6 8 10 12

Peak Voltage (V)

THD

(dB

)

Measured THD Simulated THD

Peter R. Wilson



22

Packaging OptionsPackaging OptionsAs well as wire wound, integrated inductive components As well as wire wound, integrated inductive components (planar devices) were tested and compared with standard (planar devices) were tested and compared with standard wire wound (EP13) cores:wire wound (EP13) cores:

Package

Ferrite

Pins

[a] side view

[b] plan view [c] 5:5T PCB Layout

InternalTracks

Peter R. Wilson



23

EP13 and IIC ComparisonEP13 and IIC ComparisonThe generic planar device is much worse than the EP13 core, The generic planar device is much worse than the EP13 core, and this is predicted by the simulationand this is predicted by the simulation

-70

-60

-50

-40

-30

-20

-10

0

0 2 4 6 8 10 12

Input Voltage (V)

TH

D (d

B)

IIC EP13

Peter R. Wilson



24

Conclusions thus farConclusions thus farSmaller ER and Smaller ER and toroidtoroid cores are not good enoughcores are not good enough

• Basically too small – saturate early• Not enough inductance• Not enough air gap relative to core size

Integrated Inductive Components not good enoughIntegrated Inductive Components not good enough• Too few turns• No gap

What about custom planar devices?What about custom planar devices?• More turns• Custom gap• Low profile = better density of ADSL modem in exchange

Peter R. Wilson



25

Custom Planar TransformersCustom Planar TransformersUsing a customised planar device, with a large enough core Using a customised planar device, with a large enough core (predicted by the simulation) to ensure low distortion, the (predicted by the simulation) to ensure low distortion, the tests were repeated using an E18 coretests were repeated using an E18 core

Peter R. Wilson



26

E18 Custom Planar DeviceE18 Custom Planar DeviceThe resulting THD figures were comparable with the standard The resulting THD figures were comparable with the standard EP13 EP13 wirewoundwirewound devicedevice

-70

-60

-50

-40

-30

-20

-10

0

0 2 4 6 8 10 12

Input Voltage (V)

TH

D (d

B)

APC4199 E18 (no gap) E18 (Gapped)

Peter R. Wilson



27

ConclusionsConclusionsBehavioural Behavioural modelingmodeling has been used in a range of ADSL has been used in a range of ADSL transformers to predict:transformers to predict:

• Insertion Loss• Bandwidth• Distortion

Simulation has been used effectively to guide the design of Simulation has been used effectively to guide the design of the proposed transformers to meet the requirements of the the proposed transformers to meet the requirements of the ADSL design contextADSL design contextNew planar devices have been implemented that will greatly New planar devices have been implemented that will greatly improve improve produceabilityproduceability and packing densities in exchanges.and packing densities in exchanges.

predicting total harmonic distortion (thd) in adsl ... · adsl transformer design issues the adsl...

Documents