Test Strategies for High-

Frequency Wideband

Vector Analysis

Walt Schulte

Applications Engineer

Microwave and Communications Division

Agilent Technologies

10/16/2012

2

Agenda

• Nonlinear Distortion

• Methods to Characterize Nonlinear Distortion

• Two-Tone Measurements

• Multitone Measurements

• CCDF Measurements

• Noise Power Ratio (NPR) Measurements

• Making Wideband High Frequency Measurements

• Making Vector Based Measurements

10/16/2012

Linearity Concerns

4

Signals can interact

Non-linear power amp

Spectral re-growth

Unusable bandwidth

Need to characterize

H V

H V

10/16/2012

5th order

IMD

Nonlinear Distortion: Intermodulation

7

Amplifier

In Out

(3A-2B)

(2A-B)

(3B-2A)

2nd

harmonics

3rd

harmonics

2B 2A

f A B

3rd order

IMD typical

channel

bandwidth

(2B-A)

3A 3B

A B

2nd order

IMD

A B

(B-A)

Intermodulation

distortion

3rd order

IMD

5th order

IMD

10/16/2012

Non-Linear Distortion: Spectral Re-Growth

Page 8

Pt

Pi

f

Spectral

‘Re Growth’

Non-Linear

Effect

8

10/16/2012

IMD and Spectral Re-Growth

9

Pt

f

A B

A+

A

A+

B

B+

B

A+

A–

B

B+

B–

A

Pt

Pi

IMD3

Distortion

TOI or IP3

IMD3

Fundamental

Pt

f

A B

A+

A–

B

B+

B–

A

IMD3

1st, 2rd, 3th, etc.

harmonics mix together

forming IMD

10/16/2012

Two Tone or TOI Test

10

Advantages

• Quick test

• Simple to perform

• Uses common test equipment

• High signal to noise

Disadvantages

• Essentially narrow band

• Requires wideband matching

• Does not simulate correct loading conditions

• Probably needs components to increase source

to source isolation

10/16/2012

PXA performance

spectrum analyzer

PSG

CW signal generators

Traditional Two-Tone Measurements

11

DUT

LPF

Combiner

Isolator AMP

Attenuator

2nd & 3rd

harmonics

IMD

products

+

10/16/2012

Three Tone Testing

12

Advantages

• Reasonably quick test

• Simple to perform

• Uses common test equipment

• Better Intermodulation test

Disadvantages

• Essentially narrow band

• Requires wideband matching

• Open to interpretation

• Averaging required

3rd 5th 7th

Note:

Uses uneven spacing for tones

10/16/2012

>10 Tone Testing

13

In practice, using analog signal sources and combining techniques

proves impractical for the majority of users.

Why is this?

• < +20 dBm is typically maximum out of signal sources, but usually not

able to use this due to distortion due to the source levelling circuits

• Combiners with good port isolation have high attenuation

• Use of filters and isolators creates limited flexibility

• Post combiner amplification either not available or too expensive.

• Cost and physical size of signal sources

10/16/2012

Modern Multi-tone IMD

14

• 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

Why use multi-tone test signals?

10/16/2012

• Well established test procedure

• Common test equipment

• 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

15

Disadvantages of analog test approach

Advantages of analog test approach

10/16/2012

Analog I/Q modulation vs. digital I/Q up-conversion

Page 16

Conventional I/Q

modulation -

Analog I and Q

signals are

generated using an

AWG. An I/Q

modulator

generates the IF or

RF signal

Digital up-

conversion –

I/Q modulation is

performed digitally

- either in real-time

(in hardware) or

up-front in software

Mixer /

Multiplier

/ LO

AWG

D/A

D/A

Memory

Memory

Analog IQ Modulator

X

X

+ ~

90

AWG

Digital signal Analog signal

D/A

X

X

+ ~

90

Memory

Memory

X

~

10/16/2012

Vector Test Stimulus up to 1 GHz

17

I Q

DUT

Isolator

Dual LXI arbitrary

waveform generator

(N8241A)

(Differential)

PSG vector

signal generator

(E8267D)

PXA performance

spectrum analyzer

(N9030A)

10/16/2012

Vector Test Stimulus

18

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

• Available output power

• Carrier feed through

• Images

• Relative tone spacing

10/16/2012

• Up to 4097 tones

• Vary tone power

• Change phase settings

• Randomly spaced tones

• CCDF plot

• COM-based API

LAN/GPIB

PSG PXA

N7621A Signal Studio for Multi-tone Distortion

19

…and After

• Improved IMD

suppression

• Correct with additional

devices in the loop

• 80 MHz correction BW

(internal AWG)

• 1 GHz correction BW

(Agilent’s WB AWG)

Before…

Option 203

10/16/2012

Achieving the Right Signal Statistics

20

22 Pv

Average random power?

Noise vs. pseudo noise

Peak to average ratio

CCDF signal statistic

PSG NPR adjustable

Generator seed selectable

20

t

Average

v

Power

% Time

Power

% Time

Power

% Time

Power

% Time

2

cdf1

cdf1log10

CCDF

10/16/2012

Complementary Cumulative Distribution Function

21

Link- CCDF demo video

10/16/2012

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

E8267D PSG

Enhanced Multi-tone Measurements

22

DUT

N9030A PXA

10/16/2012

Complicated Loading Scenarios: NPR

23

Multiple signal bandwidths, amplitudes & modulation types

3rd’s, 5th’s, etc… Can add together

Difficult to predict, so measure with NPR test

?

f

10/16/2012

NPR Measurement Overview

24

Notch

Depth

No

tch

Frequency

Amplitude

Broadband Noise

Notch

Depth

Frequency

Amplitude Notch Bandwidth

Spectral Re-Growth

NPR

10/16/2012

Traditional NPR Test Setup

25

LO

RF IF

Up converter

Noise Source

Band stop

filter

Spectrum analyzer

CW signal generator

DUT

10/16/2012

Traditional NPR Test Problems

26

Notch filter shape issues

Depth & bandwidth

Filter Q requirement

Cavity filters

Fixed center frequency

Noise flatness

Test station correlation

Notch

Depth

Frequency

Power Notch Bandwidth

NPR

Band Stop

Filter

10/16/2012

PXA Performance

Spectrum Analyzer

(N9030A)

I Q

DUT

(Differential)

27

Arbitrary Waveform Generator for NPR

Dual LXI arbitrary

waveform generator

(N8241A)

PSG Vector

Signal Generator

(E8267D)

10/16/2012

Using a Vector Signal Generator and an AWG for NPR

28

Repeatable, flat noise power, square notch….

Deeper notch with easily adjusted center frequency

Up to 80 MHz bandwidth in PSG & 1 GHz with the N8241A!

Conventional Analog NPR Stimulus Digitally Synthesized NPR Stimulus

10/16/2012

Signal Studio for Multitone Distortion

Option 204

29

LAN/GPIB

PSG

Digitally Synthesized NPR

Stimulus

PXA

Synthesize NPR stimulus

Vary notch depth

Vary notch bandwidth

Vary notch frequency

Distortion correction

Vary stimulus’ CCDF

10/16/2012

NPR Measurement

30

Amplifier Measurement

Notch Creation

38 GHz!

Using Noise and Band Power Markers

10/16/2012

Arbitrary Waveform Generator Requirements

31

• Wide bandwidth (1 GHz)

• High dynamic range

• Low distortion products

• Flatness

• Repeatability

• IF and IQ generation

capabilities

N6030A (PXI) N8241A (LXI)

10/16/2012

New ARB – M8190A

16 QAM Example with Analog IQ Modulation using

Vector Signal Generator

32 10/16/2012

High-Precision AWG Example: Analog IQ Modulation,

Fc=10GHz

Wideband digital

modulation:

QAM16, 1.76G Sym/s

Fs = 7.2 GHz

with amplitude

correction

EVM=1.17%

33 10/16/2012

High-Precision AWG Example: Digital Upconversion,

Fc= 1GHz (without PSG RF Sig Gen)

Wideband digital

modulation:

QAM16, 1G Sym/s

Fs = 7.2 GHz

with amplitude

correction

EVM=0.89%

34 10/16/2012

Page 35

Vector Modulation Analysis - 89600 VSA Software Use the SAME measurement tool at ALL stages of your block diagram!!!

DSP

Digital (SSI) IF/RF BB (I-Q)

Logic Analyzer Oscilloscope Signal Analyzer

DUT

Wideband High-Frequency Vector Measurement Options

Page 36

Bandwidth

Dyn

am

ic R

an

ge

PXA 160MHz

@78 dB

Wide Band VSA

(PXA + Infiniium)

900 MHz @ 40 dB*

X93204A Infiniium scope

32 GHz @ 40 dB

MXA 25MHz

@78 dB

10/16/2012

Instrument and System Calibration

Page 37

Calibration

Amplitude Flatness Phase linearity

Minimum Error Vector Magnitude EVM

I

Q

Ideal Signal

Measured

signal

θ

Amplitude error

Phase linearity error

The goal is to measure the EVM of the DUT not the

EVM introduced by the measuring system

10/16/2012

0-3.6 GHz low band

3 Hz-26.5 GHz

Input

Cal input

2 dB-step mech atten

μW converters

8.3-14 GHz LO

10.9M

.3M

4.8 GHz LO

RF converter

3.8-8.73 GHz LO

2nd converter

FPGA

300 MHz LO

200 MHz CK

100 MHz CK

ADC

ADC

Switched filters,

F0=22.5 MHz

X1 3.6-13.6 GHz

X2 13.6-26.5 GHz

140 MHz

3.5-26.5 GHz high band

FPGA

140 MHz Front End

Swept IF & 10 MHz BW

& 25 MHz BW (option B25)

25 MHz

966K

303K

79K

9K

Switched filters,

F0=322.5 MHz

140 MHz BW (option B1X)

2 2 6 10 20 30

RF preamp

40 MHz

400 MHz CK

40 MHz BW (option B40)

ADC

F0=250 MHz

F0=300 MHz

F0=322.5 MHz

Linearity

Corrections

Low noise path

μW preamp

YIG filter with

bypass relay

1 dB-step electronic atten

F0= 5.1225 GHz

4 GHz

ASIC

2Gbyte

SDRAM

ASIC

2Gbyte

SDRAM

PXA Simplified Block Diagram

38 10/16/2012

Example of Quality of Magnitude and Phase Corrections

on 140 MHz BW

EVM Results for 138 MHz OBW QPSK Signal vs. Center Frequency in Band 0

39 10/16/2012

PXA Simplified Block Diagram (900 MHz IF Path)

40

3 Hz-26.5 GHz

Input

8.3-14 GHz

3.6-13.6 GHz Path

3.5-26.5 GHz high band

Front End Low noise path

μW preamp

YIG filter with

bypass relay

13.6 - 26.5 GHz Path

Aux IF out

Option CR3 Option MPB

Rear Panel

900 MHz IF BW centered at 600 MHz

10/16/2012

Setting up the Vector Signal Analyzer

Page 44

1. Connect a source to

the PXA

2. Connect the VSA the

scope over the LAN, and

the PXA’s wideband IF

output to channel 1 of

the scope’s input

10/16/2012

Setting up the Vector Signal Analyzer

Page 45

3. Configure the VSA for use

with a downconverter.

10/16/2012

Correcting Downconverter Frequency Response

Page 46

1. Configure your

source for a 0 dBm

CW at the desired

carrier

2. Set VSA averaging

to “continuous peak

hold”

10/16/2012

Correcting Downconverter Frequency Response

Page 47

1. Program your source to

slowly sweep across the

desired band

2. Be sure that the ADC is not

being overdriven during the

sweep.

3. Use an external leveling

loop if necessary

10/16/2012

Applying Frequency Response Corrections

Page 48

1.

2.

10/16/2012

Applying Frequency Response Corrections

Page 49 10/16/2012

Amplitude Corrections

Page 50 10/16/2012

Vector Analysis with Wideband QPSK, APSK, and

SOQPSK Agilent 89601B VSA

Page 51

10 GHz QPSK signal

BW = 900 MHz and

EVM = 1.4%

APSK and SOQPSK

10/16/2012

Summary

52

Nonlinear behavior must be characterized and addressed

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

Digital signal generation approach provides repeatability and cost advantages over analog

generation approaches including notch depth, bandwidth, and adjustability

Multiple techniques and measurements non-linear behaviors in the PXA

Using the PXA as a down-converter is a technique for lower cost high-frequency

wideband measurement

VSA software enabled is a flexible platform that allows for easy input of corrections as

well as a platform to make a large amount of vector/modulation quality measurements

10/16/2012

Thank You!

53

10/16/2012