11 09 1213-01-00ad 60ghz Impairments Modeling

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Vinko Erceg, BroadcomSlide 1

60 GHz Impairments Modeling

Date: 2009-11-19

Authors:

Name Affiliations Address Phone Email

Vinko Erceg Broadcom San Diego 858 521-5885 [email protected]

Murat Messe Broadcom

Alireza Tarighat Broadcom

Michael Boers Broadcom

Jason Trachewsky Broadcom

Changsoon Choi IHP [email protected]


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Revision History

Rev1: Phase Noise and CMOS PA AM-AM model

parameters were updated


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Outline

PA non-linearities (distortion) modeling

PA Output Backoff (OBO)

Phase noise modeling

Carrier frequency offset and symbol clock modeling I/Q Imbalance modeling


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PA Non-Linearities Modeling (1)

Input signal x(t)to an amplifier produces output signaly(t):

PM)-(AMdistortionphasetheis))((

AM)-(AMdistortion(gain)amplitudetheis)(

where

))(()(2cos)(

))(2cos()()(

tA

tAG

tAttftAGy(t)

ttftAtx

c

c


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PA Non-Linearities Modeling (2)

Popular approaches to model G and are: Saleh Model [1]

Both amplitude and phase distortion are modeled

This model was originally developed for the Traveling Wave Tube Amplifiers

(TWTA) For some parameter settings output power decreases as input power increases

May be used for some Solid State Power Amplifier (SSPA) applications

Rapp model [2] Originally developed to model only amplitude distortion

Suitable for SSPA modeling

Modified Rapp Model [3,5] Phase distortion modeling was added Suitable for SSPA modeling

Ghorbani model [4] Both amplitude and phase distortion is modeled

Suitable for SSPA modeling


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Ghorbani Model

Both amplitude and phase distortions are modeled by 4 parameters:

A1

)(

A1)(

4

3

1

43

1

2

2

2

2

yAy

AyA

xAx

Ax

AG

y

y

x

x


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Rapp AM-AM Model

Amplitude distortion (AM-AM) in Rapp model is modeled as:

levelsaturationtheis

factorsmoothnesstheis

signalgainsmalltheis

where

1

)(2

12

sat

ss

sat

A

s

g

A

gA

AgAG


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Modified Rapp AM-PM Model

See reference [3] for modified Rapp model that includes also phase

distortion modeling

Phase distortion (AM-PM) may be also modeled as:

The above equation is used for our modeling purposes

2

1

1

)(q

q

A

AA


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802.11n PA Distortion Model [7] Example

IM1 PA non-

linearity

Simulation should be run at an oversampling rate of at least 4x. Use RAPP power

amplifier model as specified in document 00/294 with p = 3. Calculate

backoff as the output power backoff from full saturation:

PA Backoff = 10 log10(Average TX Power/Psat).

Total TX power shall be limited to no more than 17 dBm.

Disclose: (a) EIRP and how it was calculated, (b) PA Backoff, and (c) Psat per PA.

Note: the intent of this IM is to allow different proposals to choose different outputpower operating points.

Note: the value Psat = 25dBm is recommended.

Note: AM-PM is not modeled


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GaAs PA Model (1)

GaAs PA Model

In [5], a 802.15.3c PA distortion model was proposed based on theGaAs pHEMT 60GHz HPA measurements from NEC

The NEC GaAs PA characteristics seem to have similar trend to otherpublished/measured amplifier characteristics in this class

Characteristic AM-AM and AM-PM curves

Modified Rapp or Ghorbani models may be used for fitting the AM-AMand AM-PM experimental data points

We use modified Rapp model

Least squares fitting function

Voltage is rms

Highest voltage AM-PM point was not included in the modeling (does notfollow trend)


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GaAs PA Model (2)


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GaAs PA Model (3)


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GaAs PA Model (4)

Modified Rapp model parameters for NEC GaAs PA

AM-AM parameters

g= 19

Asat= 1.4

s = 0.81

AM-PM parameters

= - 48000

= 0.123

q1 = 3.8

q2 = 3.7


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CMOS PA Model (1)

We use the measured data from a 65 nm CMOS 60 GHz

PA in reference [6]

Modified Rapp or Ghorbani models may be used for fitting the AM-

AM and AM-PM experimental data points

We use modified Rapp model

Least squares fitting function

Voltage is rms

AM-PM response was normalized so that the first point has Phase = 0o


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CMOS PA Model (2)


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CMOS PA Model (3)


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CMOS PA Model (4)

Modified Rapp parameters for CMOS PA

AM-AM parameters

g= 4.65

Asat= 0.58

s = 0.81

AM-PM parameters

= 2560

= 0.114

q1 = 2.4

q2 = 2.3


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PA Output Backoff (1)

PA Output Backoff (OBO) may be defined as:

where P is either PA saturation point or 1 dB PA compression point

OBO is related to: Meeting spectrum mask requirements

Increasing modulation accuracy (reducing EVM)

Reducing Adjacent Channel Interference (ACI)

P

PowerTXAverageOBO

__log10 10


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OBO values for OFDM system reported in [9-11] relative to the 1 dB

PA compression point are approximately 6 dB for 64 QAM

modulation with R = coding

OBO value for OFDM system reported in [10] relative to the PAsaturation point is approximately 9 dB for 64 QAM modulation with

R = coding

OBO values for OFDM system reported in [11] relative to the 1 dB

PA compression point are approximately 4.5 dB for 16 QAM

modulation with R = coding (performance degradation of 1.5 dB) Theoretical OBO value for Single Carrier (SC) GMSK modulation is

0 dB

OBOSC_GMSK= 0.5 dB may be used


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Modulation Accuracy (dB)

EVM

OBO (dB)Spectrum Mask

Requirements

Mod. Accuracy

Requirements

OBO Requirement


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Phase Noise Model (1)

Phase noise may be reasonably modeled by a two pole

one zero model

We propose the following parameters of the model:

PSD(0) = -90 dBc/Hz Pole frequencyfp = 1 MHz

Zero frequencyfz= 100 MHz

PSD(infinity) = -130 dBc/Hz

))/(1

)/(1)0()( 2

2

p

zff

ffPSDfPSD


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Phase Noise Model (2)


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Frequency Offset/Symbol Clock Accuracy

Symbol clock frequency tolerance in most systems is

specified at +/- 20 ppm

Reasonable cost/performance tradeoff

Frequency offset of13.675 ppm at the receiver,

relative to the transmitter may be used [7]

The symbol clock of the same relative offset as the

carrier frequency offset may be used


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I/Q Imbalance Modeling (1)

Following model may be used for I/Q imbalance modeling [8]:

where y(t)is the ideal complex transmit signal, yd(t)is the distorted

complex signal, and distortion coefficients are given as

where and are phase and gain imbalances, respectively

)(*)()( tytyty rrd

)2/sin()2/cos(

)2/sin()2/cos(

rrrr

rrrr

jv

j


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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.515

20

25

30

35

40

45

50

55

IQ gain imbalance (dB)

TX

EVM(

dB)

TX EVM vs. flat TX IQ imbalanace (with no pre-compensation), TX Floor SNR of 50dB

Phase imb. =0

Phase imb. =1

Phase imb. =2

Phase imb. =3

Phase imb. =4

Phase imb. =5

Phase imb. =6

TxEVM(-dB)


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We propose that including I/Q imbalance in the

simulations be optional

Slides presented here regarding I/Q imbalance may

serve as a reference


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Conclusion

We propose the following impairments/parameters to

be included in the simulations:

PA distortion

OBO

Phase noise

Frequency/Symbol Clock offset

We propose that inclusion of the I/Q imbalance

impairment is optional


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References [1] A.A.M. Saleh, "Frequency-independent and frequency-dependent nonlinear

models of TWT amplifiers," IEEE Trans. Communications, vol. COM-29,November 1981, pp.1715-1720.

[2] C. Rapp, "Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal for aDigital Sound Broadcasting System", in Proceedings of the Second EuropeanConference on Satellite Communications, Liege, Belgium, Oct. 22-24, 1991, pp.179-184.

[3] M. Honkanen and Sven-Gustav Haggman, New Aspects on Nonlinear PowerAmplifier Modeling in Radio Communication System Simulations, Proc. IEEEInt. Symp. On Personal, Indoor, and Mobile Comm, PIMRC 97, Helsinki, Finland,Sep.1-4, 1997, pp. 844-848.

[4] A. Ghorbani, and M. Sheikhan, The effect of Solid State Power Amplifiers(SSPAs) Nonlinearities on MPSK and M-QAM Signal Transmission, Sixth Int'lConference on Digital Processing of Signals in Comm., 1991, pp. 193-197.

[5] IEEE Document 15-06-0477-01-003c-rf-impairment-models-60ghz-band-

sysphy-simulation.pdf. [6] Mikko Varonen, et. al.Millimeter-Wave Amplifiers in 65-nm CMOS.

ESSCIRC 2007. 11-13 Sep. 2007. pp. 280-283.

[7] IEEE Document 11-03-0814-31-000n-comparison-criteria.doc.

[8] Alireza Tarighat,and Ali H. Sayed, Joint Compensation of Transmitter andReceiver Impairments in OFDM Systems, IEEE Transactions on WirelessCommunications, VOL. 6, NO. 1, January 2007, pp. 240-247.


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References

[9] Yongwang Ding and Ramesh Harjani, A High-Efficiency CMOS +22-dBm

Linear Power Amplifier, IEEE Journal of Solid-State Circuits, VOL. 40, NO. 9,

September 2005, pp. 1895-1900.

[10] Mostafa Elmala, Jeyanandh Paramesh, and Krishnamurthy Soumyanath, A

90-nm CMOS Doherty Power Amplifier With Minimum AM-PM Distortion,

IEEE Journal of Solid-State Circuits, VOL. 41, NO. 6, June 2006, pp. 1323-1332.

[11] Mathias Pauli, Udo Wachsmann, Magnus Sundelin, and Peter Schramm,

Transmitter Impairments in OFDM-Based Wireless LAN, Vehicular Technology

Conference, 53rd VTC 2001 Spring, VOL 1, 6-9 May 2001, pp. 692696.

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