December 2002December 2002

Generation and Conditioning of Multitone Test Signals

Generation & Conditioning of Multitone Test Signals

Agenda

• Linear vs. nonlinear behavior

• Nonlinear distortion

• Methods to characterize nonlinear distortion

• Two-tone measurements

• Multitone measurements

• Noise power ratio (NPR) measurements

• Summary

Output

Linear versus nonlinear behavior

Linear behavior: input and output frequencies are

the same (no additional frequencies created)

output frequency only undergoes magnitude and phase change

Frequencyf

1

Time

Sin 360o * f * t

Frequency

A phase shift = to * 360o

* f

1f

DUT

Time

A

to

A * Sin 360o * f (t - to)

Input Output

Time

Nonlinear behavior: output frequency may undergo

frequency shift (e.g. with mixers) additional frequencies created

(harmonics, intermodulation)

Frequencyf

1

Nonlinear distortion

Linear behavior

Vin = Vacos(wat)Amplifier

[A]Vout = AVin

A A

Linear behaviorVs.

Non-linear behavior

Vin = Vacos(wat)Amplifier

[A]Vout = AVin + A1(Vin)2 + A2(Vin)3 +…

harmonic distortion

A A 2A 3A

2nd

harmonic

3rd

harmonic

5th orderIMD

Nonlinear distortion

Amplifier

In Out

(3A-2B)

(2A-B)

(3B-2A)

2nd

harmonics

3rd

harmonics

2B2Af

A B

3rd orderIMDtypical

channelbandwidth

(2B-A)

3A 3B

A B

2nd orderIMD

A B

(B-A)

Intermodulationdistortion

3rd orderIMD

5th orderIMD

Methods to characterize nonlinear distortion

ACPR

AM - AMAM - PM

NPR

Multitone

Two-tone

PSA performance spectrum analyzerPSA performance spectrum analyzer

PSG CW signal generators

PSG CW signal generators

Two-tone measurements

DUT

LPF

Combiner

Isolator AMP

Attenuator

2nd & 3rd

harmonicsIMD

products

2nd

3rd

f

Q

VGS

IDS

VInput

• 1st, 2rd, 3th, etc. harmonics mix together forming IMD

• Power source cannot supply current

IOutput

• “Clipped” sine waves Fourier transform

• Rate of compression determines harmonic amplitude & IMD Tones

POutput

PInput

Two-tone IMD

Amplifier linearity behavior & common metrics

IP3 or TOI

POutput

PInput

“linea

r”

• Linear amplification

• Saturated power

• Gain compression

• Power at 1 dB of compression

• Two-tone intermodulation (IMD)

• Third order intercept point (TOI)

Psat.

P1dB

P3rd P5th

Amplifier

PowerIn

AB AB

PowerOut

Multitone IMD

Why use multitone test signals? Why use multitone test signals?

•For wideband components two-tone measurement results vary depending on tone spacing

•Simulate real-world operating conditions

•Stress device with higher peak-to-average ratio

•Test with multiple phase sets

Effect of phase relationships…on peak-to-average ratioPSG CCDF PlotsPSG CCDF Plots

Equal phase set peak-to-average

17.88 dB

Random phase set peak-to-average

6.70 dB

63-tone signal63-tone signal

Effect of phase relationships…on IMD performance

Random phase set #13rd order IMD

-60.22 dBRandom phase set #2

3rd order IMD -48.65 dB Equal phase set

3rd order IMD -52.89 dB

Conventional analog test stimulus

DUT

LPF

Combiner+

+

+

Isolator AMP

PSG CW signal generators

PSG CW signal generators

PSA performance spectrum analyzerPSA performance spectrum analyzer

Advantages of analog test approach Advantages of analog test approach

•Well established test procedure

•Common test equipment

Disadvantages of analog test approach Disadvantages of analog test approach

•Complicated test setup

•Signal parameters are not easily modified

•Manual tuning

•Difficult to generate random phase sets

•Equipment and capital intensive

Conventional analog test stimulus

Vector test stimulus

I Q

Internal Baseband Generator

Internal Baseband Generator

E8267C PSG Vector Signal

Generator

E8267C PSG Vector Signal

Generator

DUT

Isolator

Multitone Number of tones: 2 to 64Vary tone spacing: 100 Hz to 80

MHz (2-tone)Tone power: 0 to –40 dBInitial phase: fixed or random

E8267C PSG vector signal generator personalities

Two-tone Vary tone spacing: 100 Hz to 80 MHz

Two-tone Vary tone spacing: 100 Hz to 80 MHz

•Up to 64 tones

•Vary tone power

•Change phase settings

•80 MHz correction BW

•CCDF plot

•COM-based API

LAN/GPIB

PSG PSA

E8267C PSG vector signal generator personalities…and After

• Improved IMD suppression

•Correct with additional devices in the loop

Before…Signal Studio

for Enhanced Multitone

(opt. 408)

IMD products from DUT

Low IMD reduces test uncertainty

Tone correction Minimize test stimulus IMD …

even at the output of an external power amplifier!

Non-linear distortion measurement

E8267C PSG

E4440A PSA

Enhanced Multitone Measurements

DUT

Vector test stimulus

Advantages of vector test approach Advantages of vector test approach

•Simple test setup and procedure

•Easily modify signal parameters

•Apply pre-distortion to improve signal quality

•Repeatable and accurate test results

•Save time and capital equipment cost

Disadvantages of vector test approach Disadvantages of vector test approach

•Available output power

•Carrier feed through

•Images

•Relative tone spacing

Traditional NPR test methods

LO

RFIF

Up converter

Noise Source

Band StopFilter

Noise generatedBy DUT

NPR

Noise Stimulus

Measurement Bandwidth

DUT

PSA performance spectrum analyzerPSA performance spectrum analyzer

PSG CW signal generators

PSG CW signal generators

NPR challenges and alternatives

• CHALLENGES:

• Need signal generator + AWGN

source + band stop filter

TIME & COST

• AWGN is constant only if measured

in a long period

REPEATABILITY

• ALTERNATIVE:

• Use multiple tones with a large tone

density to simulate noise signal

Features

•Vary tone spacing and notch depth

•Distortion correction

Value •Simplified test setup•Repeatable test results

Features

•Vary tone spacing and notch depth

•Distortion correction

Value •Simplified test setup•Repeatable test results

NPR

wideband component

and satellite test

wideband component

and satellite test

ComingSoon

Signal Studio for

NPR

E8267C PSG Vector Signal Generator personalities

LAN/GPIB

PSG PSA

Summary

• Nonlinear behavior must be characterized and addressed to minimize in-band and out-of-band interference

• Distortion Measurements are typically performed using CW signals

• Common test signals include two-tone, multitone, and NPR signals

• Digital multi-tone generation approach provides repeatability and cost advantages over analog generation approaches

• Digital generation approach uses pre-distortion to improve dynamic range, which can minimize cost and setup time

Where to find additional information…

[1] Kent K. Johnson, Agilent Technologies, “Predicting BER II –Measurements for Lowering Radio Cost”, http://www.agilent.com/find/BroadbandSymp/

[2] “Characterizing Digitally Modulated Signals with CCDF curves”, Agilent Technologies Application Note, literature number 5968-6875E

[3] “Spectrum Analysis Basics”, Agilent Technologies Application Note 150, literature number 5952-0292

[4] “Optimizing Dynamic Range for Distortion Measurements”, Agilent PSA series Product Note, literature number 5980-3079EN

[5] www.agilent.com/find/psg

[6] www.agilent.com/find/signalstudio

[7] www.agilent.com/find/psa