understanding low phase noise signals · each type of noise process has distinct characteristics...

Agilent Copyright 2014

Understanding Low

Phase Noise Signals

Presented by: Riadh Said

Agilent Technologies, Inc.


Introduction

Instabilities in the frequency or phase of a signal are caused by a number of different effects.

Each type of noise process has distinct characteristics that can be measured using time

domain and frequency techniques.

In many cutting edge radar and communication systems, phase noise is the characteristic

that limits the system performance. In radar systems, phase noise degrades the ability to

process Doppler information in radar. And, in digitally modulated communication system,

phase noise degrades error vector magnitude.

I

I

Frequency

Instability

Effects

Q

3 Agilent Copyright 2014

Phase Noise can Matter:

Getting the Best Possible Performance

– Phase noise may be limiting parameter in measurement/sys. performance

Balancing Phase Noise with Cost, Other Factors

– How to identify, quantify effects

– Identifying When it’s Not Important

Phase Noise Tradeoffs

– Acquisition cost

– Switching speed

– Frequency and offset noise

3

•A Lot

•Some

•Not At All


Agenda

• Frequency Stability

– Terminology & representation

– Architecture implications

• When Phase Noise Matters

– Example: Doppler Radar

– Example: Phase noise and EVM in OFDM signals

– Degrading phase noise performance for real-world signal substitution

• Signal Generator Choices, Performance & Tradeoffs

• Getting the Most from the Signal Generator You Have

4


Random perturbations that

appear as instabilities in

frequency can be represented in

either the frequency domain or

the time domain.

• Frequency Domain

- Frequency Offsets of a few Hz

to tens of MHz

• Time Domain

- For close-in noise (<<1 Hz)

- Short-Term Stability

5

Frequency Stability: Frequency & Time Domain Measurements


Frequency Stability: Short & Long Term

Terms, Measurements, Displays

Short Term Stability

• Short term = seconds

• Terminology: Phase Noise, Jitter

• L(f) curves, integrated totals, spot

measurements, jitter (p-p)

• Can be a function of both signal

generator and frequency reference

Long Term Stability

• Long term = minutes - years

• Terminology: Accuracy, drift, aging

• Often determined by frequency

reference

Understand Your System and

its Sensitivity vs. Frequency

6

Detail References Phase Noise Measurement Methods

and Techniques


Pedestals, Slopes & Bumps: Signal

Generator Architecture & Phase Noise

Example: Agilent PSG Microwave Signal Generator

7

Reference Section

Synthesizer

Section YIG

Oscillator

Output

section

Detail References Reducing Phase Noise at Microwave

and RF Frequencies


Agenda










8


When Phase Noise Matters

Matters More

• Doppler RADAR

• OFDM

• Oscillator substitution

• ADC testing

Matters Less

• OFDM (matters more and less, depending on offset)

• Wideband single-carrier modulation

• Harmonic distortion testing

• Wideband ACPR testing

• Amplifier gain testing

9


Example: Phase Noise Doppler RADAR

10


Phase Noise and RADAR Applications

Doppler Example

11

F 0 Fd1

BW = 1/t

STALO phase noise sidebands

with no target clutter

STALO

LNA IFA

PA

F0

F0r + Fd1

Pt

Pr


and RF Frequencies


Doppler Frequency Shift and

Phase Noise Offset Frequencies

Close-In (example: Airport Surveillance Radar)

• 100 mph, S-band (3 GHz): fd = 900 Hz

Wider Offsets (example: Military Radar)

• Mach 1.5, X-band (10 GHz) fd = 33,000 Hz

12

R

Doppler Frequency fd :

Rvc

fRvfd

022

Detail References Radar & Electronic Warfare Threat

Simulation


Consider Noise Contributions from

Amplifiers, Including Broadband Noise

13

Additive noise of the transmitter

is present in the large reflected

signal from the clutter and can

mask the targets response

F0r

BW = 1/t

STALO

Pulse Mod

PA

PA

STALO

Fd2


Also Consider Spurious Performance

for RADAR and EW Applications

14

Noise and Spurious Effects

F 0 Fd1

BW = 1/t

Fs1 Fs2 Fd2

System Spurious Signals within the Receiver BW

STALO

LNA IFA

PA

F0,Fs1,Fs2

F0 + Fd1


F0r

BW = 1/t

Transmitter phase noise sidebands with clutter

Example: 1 GHz Doppler radar

Doppler BW = 10 kHz

Target = 1 m2

Range = 100 km

Min Det Vr = 80 knots

Clutter visibility = 80 dB

Transmitter Noise Sidebands:

L(f) < -120 dBc/Hz @

200 Hz offset

STALO

PULSE MOD

PA

PA

STALO

Fd2

Estimating Required Phase Noise

Performance

15

Detail References Introduction to Radar Systems

Skolnik


Example: Phase Noise and OFDM

16


OFDM and Pilot Tracking

Pilots Shown in Time (I/Q) and Frequency

17


OFDM and Pilot Tracking

BPSK Pilots: Demodulation Reference, No Data Transmitted

Pilot Tracking “Tracks Out” Some Freq/Phase Instability

Instability Not Just Constellation Rotation, also FFT Leakage or

Inter-Carrier Interference

18

No Pilot Tracking Pilot Tracking Enabled Common Pilot Error: Phase


Translating Phase Noise to EVM

in OFDM

Assumptions

• Estimating effects of only phase noise and broadband (wide offset) noise

• Spurious and other nonlinearities are not significant

• Equalization effective in removing linear errors

• Pilot tracking is effective to ~10% of subcarrier spacing

– Common phase error removed in demodulation

Example: WiMAX

• 10 kHz subcarrier spacing

• 10 MHz channel bandwidth

19


Integrate Power

for

Total EVM

Phase

Noise

Tracked

Out

10 MHz Channel Bandwidth

10 kHz Subcarrier Spacing

Phase Noise

Filtered Out

Example: Phase Noise Contribution to

EVM in OFDM

EVM a function of

integrated phase noise

beyond tracking BW

and inside channel BW (and correct SSB to DSB)

20

-95 dBc/Hz integ. over ~100 kHz

& Convert SSB to DSB: add 3 dB

-95 dBc/Hz + 10log(100 kHz) + 3 dB

EVM = -95 dB + 50 dB + 3 dB

EVM = -42 dB (conservative)

Error power calculated on log scale:

95 dBc/Hz pedestal


Signal Generation and Signal Analysis

for Design & System Integration

Q: Generate with no phase noise or representative amount?

A: Yes, both

– Understand ultimate performance and residual error (error budget)

– Understand phase noise tolerance, design for “just good enough”

performance

Q: Measure with pilot tracking enabled or disabled?

A: Yes, both

– Even when tracked out, phase noise can reduce demodulation margins

21


Adding Known Phase Noise Using FM

Signal Modulated with Uniform Noise

Simple Technique for -20 dB/Decade

22

Example: Agilent PSG

• Set up an signal generator for FM modulation, by selecting:

– FM path 1

– FM on

– FM deviation, as specified

– FM waveform to noise, uniform

• Ensure that noise of the PSG in FM off is at least 10 dB less than the desired calibrated noise at a desired offset frequency, to ensure accuracy.


and Techniques


Degrading Phase Noise for Accurate

Signal Substitution

Simulate VCOs, Lower-Performance Synthesizers

When “Representative” is Better than “Perfect”

Use Baseband Real-Time Processing

23


Selectively-Impaired Phase Noise

Performance

24

Llow

Lmid

f1

Lhigh

f2

Llow

Lmid

f1

Lhigh

f2

•User sets f1, f2, and Lmid

•Slope -20dB/decade below f1 and above f2

f1=5kHz, f2=500kHz,

Lmid=-80dBc

f1=10kHz, f2=1MHz,

Lmid=-90dBc


Agenda










25


Sig. Gen. Choices: Frequency Stability Narrowing the Hardware & Software Choice

CW or “Analog” vs. Digital Modulation or “Vector”

• Phase noise performance choices may interact with other capabilities

– Internal and/or external digital modulation

– Pulse modulation

– Internal/external software

– Memory and/or real-time baseband signal generation

– Power, distortion

Single-Loop vs. Multiple Loop

Phase Noise Performance Levels as Options

VCO (voltage-controlled oscillator) vs. YIG (yttrium iron garnet)

• Switching speed, phase noise, cost

26

New X-Series

Single- & Multiple-Loop Synthesizers

Single Loop (example: EXG)

• Less complex, less expensive

• Moderate performance, can

provide very good ACPR

• Simpler to design, optimize

Multiple Loop (example: MXG)

• Typically fine loop + offset/step loop

+ sum loop

• Better phase noise

• Lower spurious

• More optimization choices and

flexibility

27

EXG N5173B Microwave Analog

EXG N5172B RF Vector

MXG N5183B Microwave Analog

MXG N5182B RF Vector


1Hz 10Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz

Single vs. Multiple-Loop Architecture

New Agilent X-Series (MXG, EXG)

28

MXG enhanced low

phase noise option

MXG standard

EXG SSB Phase Noise @ 10 GHz

L(f) [dBc/Hz] vs. Frequency


MXG N5183B Analog, N5182B Vector

Spurious and Broadband Noise May be as Important

as phase noise

29

MXG std. -134 dBc/Hz typ. (20 kHz offset @ 1 GHz)

kHz

MXG opt. UNY -146 dBc/Hz typ. (20 kHz offset @ 1 GHz)

Spur/Non-Harm. -96 dBc typ.

(opt. UNY @ 1 GHz)

Broadband Noise -163 dBc typ.

(10 MHz offset @ 1 GHz)


-160

-140

-120

-100

-80

-60

-40

-20

0

1 10 100 1,000 10,000 100,000 1,000,000 10,000,000

Ph

ase

No

ise

(dB

c/H

z)

Frequency Offset from Carrier (Hz)

PSG (15 GHz)

60 GHz (15 GHz x4)

90 GHz (15 GHz x6)

120 GHz (15 GHz x8)

180 GHz (15 GHz x12)

270 GHz (15 GHz x18)

450 GHz (15 GHz x30)

Generally Worse with Increasing Frequency

Delta = 20*log(N), where N = multiplication factor

Phase Noise vs. Frequency

Agilent PSG Microwave/Millimeter Signal Generator


Phase Noise vs. Frequency

31

Agilent MXG RF Signal Generator (opt. UNY)

100 Hz 10 kHz 1 MHz 10 MHz

Not always a Simple Relationship


Oscillator and PLL Technologies Affect

SSB Curve Shape, Tradeoffs

32

New MXG vs. EXG vs. ESG @1GHz

100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz


Tradeoffs

Switching Speed

• Generally faster with VCOs (vs. YIGs)

• Faster with wider loop bandwidths

• But wider loop BW may move noise to undesirable offset region

Phase Noise

• YIGs generally better than VCOs

• Multi-loop significantly better than single-loop

• Move problem energy to a non-problem region

• Optimize for wide offsets vs. optimize for close-in

33


Other Capabilities, Tradeoffs vs. Phase

Noise Performance

Modulation Capability

• Maximum modulation bandwidth

• Modulation quality

– In-band: EVM or MER, etc.

– Out-of-band: ACPR

• Modulation inputs & outputs (bandwidths can be different)

Pulse Capability

• Complex pulse scenarios, pulse performance

– Modulation on pulses, Doppler, PRT

• Software/application support

Multi-Channel Synchronization

34


Agenda










35


Methods for Improving Signal

Generator Phase Noise

Connect to a Low-Noise External Frequency Reference

Advanced Architectural Improvements to the Reference and

Synthesizer Design

Adjustment of the Reference Oscillator & VCO PLL Bandwidth

Use of Dividers at Lower Frequencies Instead of Heterodyne

Mixing

36


and RF Frequencies


Optimizing Signal Generator Phase

Noise

Choice of External Reference Oscillator

Choosing External Reference Bandwidth

Optimizing for Close-In or Wide Offset Noise

Optimizing for Broadband Noise

Optimizing for low frequency coverage

Noise Subtraction, Including Phase Noise Subtraction

Read Documentation, Specs for Product-Specific Optimization Choices

37


1Hz 10Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz L(f) [dBc/Hz] vs. Frequency

Residual Phase Noise: Comparisons

with Perfect Reference

38

Using perfect external10 MHz reference

up to 20 dB

improvement @ 1 Hz


Residual Phase Noise: Comparisons

with Perfect Reference

39

Agilent PSG UNY

up to 20 dB improvement @ 1 Hz


Optimize Frequency Reference Choice

and Settings: Signal Analyzer Example

Quality of external 10 MHz ref. oscillators can make a big

difference in phase noise measurements (& signal generation)

40

• If an external reference

oscillator has better close-in

phase noise than the PXA the

wide locking bandwidth can

be used to obtain better close-

in (< 30 Hz) measurement

performance.

• If higher offset frequencies

are more important the narrow

setting can be used.

External reference

lock wide

External reference

lock narrow


and Techniques


Reference Oscillator PLL Bandwidth

Adjustment: PSG Signal Generator

41

The 10 MHz

reference signal

can be internally

generated or

externally supplied

Adjusting the

PLL integrator

bandwidth


and RF Frequencies


PLL Bandwidth Adjustment: PSG

Microwave Signal Generator Example

42

300 Hz

650 Hz

125 Hz

55 Hz

25 Hz

Agilent Copyright 2014 43

Optimizing Pedestal Phase Noise: PSG

Microwave Signal Generator Example


Optimizing Signal/Noise vs.

Phase Noise

44

10 kHz 1 MHz 10 MHz


Generating Lower Frequencies:

Freq. Division vs. Heterodyne Mixing

Frequency division reduces the phase noise sidebands of the

signal by a factor of 20 dB/decade or 6 dB/octave

• Example: Dividing by 4 reduces phase noise by 12 dB. (20*log(1/4) )

Divider tradeoff: Maximum FM and PM deviations are reduced

by the same factor as the division number

Heterodyne mixing provides fine frequency adjustment while

retaining full bandwidth FM and PM

Heterodyne mixing tradeoff: Heterodyne mixing to lower

frequencies provides no phase noise reduction

45


Subtracting Signal Generator Phase

Noise Power In some scalar (power) measurements the phase noise

contribution from the signal generator can be subtracted from

the measured result

46

Raw measurement Reference measurement Result after subtraction


Subtracting Signal Generator

Broadband Noise Power

47

B M a r k e r 4 4 3 0 5 9 0 . 3 8 1 H z - 1 3 5 . 7 7 5 d B m / H z

T R A C E A : F 1 P S D 1 / K 1

A M a r k e r 4 4 3 0 5 9 0 . 3 8 1 H z - 1 2 3 . 6 d B m / H z

C e n t e r : 4 . 4 2 0 7 7 7 8 8 1 M H z S p a n : 5 0 k H z

- 5 0

d B m / H z

- 1 5 0

d B m / H z

L o g M a g

1 0

d B

/ d i v


Noise Sidebands May Not Be Entirely

Phase Noise

AM Noise may be Significant Fraction of Noise Sideband Power

AM Noise may Affect a System or Not

• Example: Pilot Tracking Usually Removes Close-In AM Noise

48

• AM noise is included in direct

noise sideband measurements

• X-Series phase noise meas.

app (N9068A) can reject AM

noise < 1 MHz

• AM rejection can improve phase

noise measurements

• Understand system sensitivity,

signal generator AM noise

AM Rejection

off

AM Rejection

on


and Techniques


Phase Noise can Matter:

Getting the Best Possible Performance

– Phase noise may be limiting parameter in measurement/sys. performance

Balancing Phase Noise with Cost, Other Factors

– How to identify, quantify effects

– Identifying When it’s Not Important

Phase Noise Tradeoffs

– Acquisition cost

– Switching speed

– Frequency and offset noise

49

•A Lot

•Some

•Not At All


References, More Information

“Techniques for Improving Noise and Spurious in PLLs” Eric Drucker,

Microwave Journal, May 2012

“Reducing Phase Noise At Microwave and RF Frequencies” Agilent A/D

Symposium 2011

“Signal Generators Provide Perfect and Precisely Imperfect Signals” Ben

Zarlingo, Microwave Journal, May 2012

“Testing Low-Noise Components in Pulsed or Moving Target Radars” Agilent

A/D Symposium 2009

“Phase Noise Measurement Methods and Techniques” Agilent A/D

Symposium 2012

“Radar & Electronic Warfare Threat Simulation” Agilent A/D Symposium 2011

“Introduction to Radar Systems” by Merrill Skolnik, 2002,

ISBN 978-0072881387

understanding low phase noise signals · each type of noise process has distinct characteristics...

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