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I
I
o The "Arl" of
Phase Noise
f,lleasurement
DieterScherer
March1985
o
Rf & Mlcrowave
Measurement
Symposlum
ancl
txhlbltlon
ftE'HF$|IfJJ
o
O
o
o
DUCTION
INTRO
Measuring and specifying phase noise has become inereasingly important as phase
noise is the limiting facior in many RF and microwave systems,like Doppler radar and
space telemetry sy.te-. or communicationlinks. The complexity and subtleties of the
1nuurur.-unt have earned it the reputation of being more art than science.
This paper gives an introduction to phase noise measurementfocusing on the two most
and useful techniques,the "Two Source Phase Detector" and the "Delay Line
Frequenc;- Discriminator" methods. System limitations are pointed 9ut a-swell as the
"o--o1
potential ,our"". of erroneousdata when phase noise is measuredin a bench set up.
The lt72gc Carrier Noise Test Set is HP's latest contribution in this field, designed to
simplify and automate the complex task. A table of comparisons will show where the
ttTigC and the various other HP solutions are optimally employed.
O 1. Phase
Why Measure Noise?
Phasenoisecauses . .
.
environment
sensitivity multi-signal
o Lowerreceiver in
Transmiller
H
q-
DopplerSignal
DecorrelatedClutler Noise
J_
o Glutter RadarSystems
noisein Doppler
r Phase systems
errorsin digitalcommunication
phasenoiseimposes fundamentallimitations wherevera weak signal is processed the presence a
in of
.tiorrg interferini rij""r. In the aboveexample, phasenoisesidebands the receiverlocal oscillatorare
of
ti"".i"*"a to thI Ifpioduct of the strong interfering sjsnll and cover up the weak wanted signal.
signal in this caseis
A similar situatio;exists with cohereit Dopplerradar. The strong interferring
p;;;;J ty reflectionsfrom large stationarl' f5;".ts. Phasenoise side bands of this unwanted return
weak Dopplersignal'
lien"i"r. ,iecorrelateJbvdelav ind potentially coveras clutter noisethe
Phasenoise adds to
b,,r"n in the world of d-igitaliata tiansmission phasenoise is a limiting faetor.
the carrier or data clock
o*,"r^il system rroir. in.rJ"sing Bit Error Rate and may causea cycle slip in
recovery.
5
2. Noise
BasicRepresentation Phase
of o
2.1 In the Time Domain:
v(t): Signat
withrandom phasefluctuation ,0(t)
A
v(t): Vscos f?rtsl+ J O (t)l
DisPlaY
OscilloscoPe
V(t) = Vs cos 2rlsl
ar <> ao(t)
bY
Frequency Phase related
and are
f(r):##
In the time domain phase noise can be observedas phase jitter of the signal on an oscilloscopedisplal' or
a time interval counter may detect the instantaneous time fluctuations of the zero crossings.
phase or frequencyfluctuations are the same physical phenomena.One can be derivedfrom the other as
angular frequency is the first derivative of phase with respect to time.
6
O,, Domain:
In the Frequency
FJd(t):Jd(f)
S4
Fluctuations
Density Phase
Spectral of
SO(f)-Jd2rms(f)
f'3 F l i cke r FM
I d2rms
f' 2 Random W alk Phase
t-t FlickerPhase
fo White Phase
FourierFrequencY -
|
s3
Fluctuations
Density Frequency
spectral of
: :
Sr t(f) = Jf2rms(f) l2J @2rms(l) fzSO(f)
Spectraldensity distributions describe frequencyor phasenoisein the frequencydomain.Terms like
.,White,,' and ..Random
,,Flicker,' Walk" refei to the slopeof f , f-t, and f-2 of thd densitydistribution.
time domain -
rrluiiipri."tion by the Fourier frequency- conespond.rlsto differentiation in the
noise.
converti the spectraldensity of phasl noiie to the spectraldensity offrequency
7
2.3 Relation Phase
of Noise
Noiseto CarrierSideband
offset
o
The modulari6n pf the signal phase manifests itself in modulation sidebandsto the carrier at
frequencies u.hich ar" muliiples of the modulation The sideband levels are
rate rFourier frequencyr.
relatedto the magnirucle the phasedeviationby Bessel
of terms.For small'anglemodulation,onl5'thefirst
Besselterm is signrficanr and the relation betu'eenphasedeviation and sidebandlevel is approximated b1'
anglemodulalion
Forsmall
( I ar. < l radian)
J d2rms
=
?P {-t d2rms(f)
A common,though indirect.representation phasenoiseis,7{fr,the ratio of the single sidebandnoise
of
po$.er in a I Hz band*'ldth to the total carrier power specified at a given offset, f of the carrier'
produce
This representation is applicable only for very small phase deviations, sufficiently small to
negligible higher order sidebands.
Definition Y (t)
ol
y(tt=ry
+- -+
-fott fogl= |
-
\
2,5 5, Sl f:
between
Refation st
8i
b
$r
lor -\6<< lradian
E!
E:
Y (t)= iS o(t)=i -t, srf (t)
1_ 11 i
E.b
.E'E
69
*l Hz
1
L
o Techniques
3 PhaseNoiseMeasurement
o DirectSpectrumAnalysis
) o Two Sources
and PhaseDetector
o Frequency
Discriminator
) o DelayLine Frequency
Discriminator
o Carrier (OndriaBridge)
Suppression
o Heterodyne
PeriodGounter
From the multitude of techniquesto measurephaseorfrequency noisetwobasicmethods are singled out
and explained in somedetail onthe following pages:the "Two Sourcesand Phase Detector" technique and
the "Dela5' Line Frequency Discriminator" technique'
Both methods are ielatively simple to implement and are broadband solutions.They also compliment
each other well. The first method rnl.rur"s phase noise;high sensitivity is obtainable and two sourcesare
needed. The second method measures frequency noise, has inherently lower sensitivity close in but no
secondsourceis required.
3.1Two Sourcesand PhaseDetectorTechnique o
Source
Test
Under
AmPl.
lsolation
lv' Low Noise
Low PassFiller Amplifier
PhaseDetector
t_
tl ^Al
(Double Mixer)
Balanced
AmPl.
lsolation Calibration
i+
I
L--
, 1! F = F
v
Allenuator
NarrowBand
PhaseLock LooP
sd (t)
y (t)
Hz)
JV273ns(1 (forJd<sd (t)=Jdimsltl=1/z
V2grms
forld<<1rad.
(1
J V2rms Hz)
=
9 $ l = 1 1 2s 6 ( l l 1 / q vzBrms
generates signal
a
With the LO and RF input in phasequadraturesteadystatewise,the mixer IF output
oroportional to the phasedifferenceof tl" two sources. linear operationthe phasedetectorcoxstant
In
;;;i;;;;;rr. of the sinusoidal beat signal producedwhen either Bource frequen-cv-offset.
is
"orftg"
Most sourc", ,nould-6rift out of quadratureover the periodof measurement. narrow band phaselock
A
l";;;;t;atically ioicesthetwo signalsinto phasequadrature. Atrates lessthan theloopbandwidth the
,ou-r.", now track each other; at rates higher than the loop bandwidt\ t-hephase fluctuations are
unaffected. The two isolation amplifiers shouldpreventinjection locking of the Bources.
phase noisemeasured the IF port represents nns-sumof the noisecontributionsof eachsource.
on the
For definite data on the sourceut d"r ttst, the phase noise of the referenceEouree should be either
well characterized. the absence any information on both sources,
In of onecan at least state
""gfigiUi. ", sourcenoise is worse than the measureddata. If 3 unknown sourcesare available, 3
that neither
accuratelyeach
i""rui"rn"nts with B different sourcecombinationsyield sufficient data to calculate
individual noiselevel.
10
O 311 The Mixeras PhaseDetector
Vg cos t,,11
Vs cos(-nt - 6(l))
v (t)= (t,n - ,L) t. O(t) +
cos ) ffi. oiL)t * o(r))+...
15
vB peak
V (t) = VBpeak ({rn - col1t. O(t))
cos KL = Conversion
Loss
VB peak= PeakVoltageof
BeatSignal
for c,rL <,.,8 and d(t) = (k +1) 90" - Jd(t)
=
JV (t) = (t) VB peaksin Jd(l)
for ld< I VoltsI
Jv (t) = (t) K6 -\d(t) K6=vBpeak L ,d J
basedon one signal gating the
The frequencyconversionof signals applied.toa.mixer |f qhvsically
other or on the nonlinear conductance oriite mixer diodes.Either caserepresents multiplying process.
a
generates productresultingin the difference
a frequency the input
of
Among many terms,ih" mixer also
signals. (linearrelationbetween and IF
RF
with a sinusoidalinput at the RF port and assuminglinearoperation
voltage),the beat sigrial is also ,it" wave with a peak voltage VB peak'The phaseslopeof this beat
signal at zerocrossings equals=" VB peak-'
setting both inpui ft;;ir t; trreiaf;6 hequencyand at a.phase offset of 90ophasefluctuationsJdrt)
Jv(t rwhich for smalllhase devjationsarelinearly related. The mixer actsas
resultin voltagefluclua"tions
a phasedeteciorwith a phasedetector constantof K6 equalto VB peak'
11
3 . 1. 2 with BeatSignal
Calibration o
Jv(f) =Kd r O(f) Ko = vB peak
: fvg 76s
1 . 1 --
J d76s(f):;; JV 765(f)- JV rms(f)
ffi-,
JV2rms (1 Hz)
=
S O(t): J d2rms(f) 172 v2Brms
e (l -- 1/2so(f): 1 / 4 JV2 rms(l Hz)
forJ 6<<1 v'B ,r,
g (t') J V 2 r m s ld B m Phasenoisespectrumin dBm
correcledfor bandwidthand
r
analyze characteristics.
-V2BrmsldBm Beatsignalin dBm.
-Kel dBm Atlenuation beatsignalwas
(if
attenuated calibration).
in
-6 dB Accounls lor rms valueof beat
signal(3 dB) and conversionof
s 6(f)roS (f) (3 dB).
+2.5dB Accounts log amPlifier
for and
videoliltering(averaging) noise
of
(if analogspectrum analYzerls
used).
Assuming VR ,.ooL as the phasedetectorconstantdictateslinear operationof the mixer. The calibra'
ti""lilr,"."p"."trtifln"lyzer for iz tf ror Sl6rfrcan then be read from the aboveequations.
PM or FM
Othercalibration methodsare basedon thllharacterization of the phaseslope, calibrated
on
sidebands one of the two sources on the injection of a calibrated
on or spurioussignal.
12
O 313 SystemNoiseFloor
lVn MtX
Jvn t.t.tr
Low NoiseAmplifier
JV2ntlttx +JV2nLNe
t system(f) =
v2g rms
The noise floor of the measurement system is establishedby the equivalent amplifier and mixer noise
tshot noise, flicher noiser at the IF port redueed by the phase detector gain K6 (VB peak for linear
operation r.System sensitivity is therefore maximized by using a high level mixer, selecting a mixer u'ith
low flicker noise and follou'ing the mixer with a low noise amplifier.
dB c
-80
N
.r Example:3047A Mixer-Amplifer MHz- 1.6GHz
5
ob -100 - SyslemNoisewlth High LevelDoubleBalanced
F@
urg Mixerand Low NoiseAmplifier
9 - ^Y
et -120
=\
urO
O-
gE -140
ACE
-tr \
6g \
U'E -160
E
\
o -
-180
lHz 1 0H z 1 00Hz 1 kHz 10kHz 100kHz l MHz
f [HzJ
t3
31.4 PotentialError Sources o
o Suppression peaking noisenearor belowthe phase
or ol
lock loop bandwidth.
o Inieclionlocking
r Deviationfrom phase (resulting an
quadrature in
lowerK6)
effectively
o Non-linear operalion mixer(if linearity
of wasassumed
in calibration)
o Distortion RF-Signal
of (resulting a deviation K6
in ol
from VB peaf)
o Saturation the preamplilier spectrum
of or in
analyzer
calibration by high spurious
or (e.9.line
signals
spurious)
o Changeof impedance while going lrom
interface
calibration measurement
to
e lnsuflicient
cancelation commonsourcenoisein a
of
residualnoisetest
r AM-noise particular noiseof the common
(in AM
noisetesl)
sourcein a residual
o Closelyspacedspurious(e.9.line multiples)
as
misinterpreted Phasenoise
circuitry (powersupply,
o Noiseinjectedby peripheral
phaselock looP)
o Noiseinjectedby peripheral (.9.,
instrumentatioh
DVM)
oscilloscope,
o Microphonic
noise.
Technique
Discriminator
Os: DelayLine Frequency
Source PowerAmPlifier
underTesl
Delay Line ( r)
Srt(t) = lf2r|nr{f)
tort=fi2JVrms = K62tr Jf *.
Jvtrms (t Hz)
srt(f)
O
7 (f) derivedfrom Srt(f) Srt(l)
JV"r. (1 Hz)
ro<<1 (tl=*irs-rtt=i +
ror :I n
6"t-
A delay line and a mixer operating as a phase detectorhave the combinedeffect of a frequency
discriminator.The delayline transformsany frequency fluctuationinto a phasefluctuationand the mixer
with the L and R inputs at g0ooffsetlinearly convertsthe phasefluctuationsinto voltagefluctuationsat
the IF port. As derivedon the next page,the equivalentfrequencydiscriminatorconstantKp is propor-
tional to r and K6.
The frequen"yio phaseconversion has a sin x/x characteristicwith a null at f = 1/r. Measurementsare
thereforelimited to f < L/Zt twith correction l.
The systemcan becalibratedby characterizing frequency
the slopegt KOand or moreconvenientlyb5'
",
.aaing fftl sidebandsto the sourcunder test ror a substitute)and determiningtheir level as reference
level with an RF spectrumanalyzer.
15
Discriminator
s.2.1 Theoryof DelayLine Frequency o
rd(r)(
v(r)=Kd rd(r)
Delay time r
t(t) = lo +Jt sin 2;ft
V(t) = Ve cos (2;fst - f .ot 2nltl
Carrierwithsinusoidal FM fs = Carrier
frequencY
| = FM rate
Jf = FM deviation
Phase Difference Phase
on Detector JO(t)
Jd(t) = Zrts(t - r)..*"ot 2rrl(r-r) - 2ilsl-f 2trlt
"ot
Jd(t) = -2rrls' .,+ (cos 2rrl(t - rl - cos 2iltl
JO(t) - 2nlsr * 2f sinzrf sinp'r 1t- 7\
= r
PhaseDetector Output:V(t) = K6 -\@(t)
=
lor 21116r (2k+1)?(PhaseQuadrature):
V(f) = KO2f sin z:'lrsin 2trt(r -il
Function:
Transfer
Jv = Ko2{sin nlr= K62,..rlt #
sin-zrfz = |
=fi:
forr tlr
JV = K6 2nr Jl
r_-
Kp t#l = Frequency Constant= K62nr
Discriminator
()szz SystemNoiseFloor
lVn urx
JVn lxa L o w N o i s eA m p l i f i e r
Srt(f ) system
DelayLine
!'r
t' Psz
(if Jdnr =
Noise RFAmplitier used):
Phase ol 1t * f t
ffi
operation): = VB peak= fiffiott
Ko (in linear Kd
with L = Conversion
Loss(Power)of Mixer
Mixer noiseand baseband amplifier noiseare interpretedby the systgmas frequencynoise.This also
holdsfor phase uv un nr amplifier.The amplifiermight have beenaddedto boostthe
"oir.l"tioJu."a
signal level lowered b1'the lossy deial'line'
':{:l;#- JV2n..nl
(X5Z--1'
Jr-l2pp
(2;rl2
1(tt=++ sYstem
srt(t) for J6<<1
, (#l' ('*f - *f - rr+23r1
,lJ.t
amplifier and RF amplifiernoiseall have a flicker noisecharacteristic closein and
Mixer, baseband
amplifier arereduced Ko u'hich
showwhite noisefarther out.The contribution. of mixer and baseband !v
p"i"t. out the benefit of the RF amplifier as it maximizesKg'"A bet*:8:Itllon, though' is to emplol' a
the needfor an RF amplifier and Yith il Jon-r"
;;;;; amplifier u.r*.-itr. signal split and eliminate
' with f-2 and f-3 towards the
S;;;;a:fn", flicker rndth"r, white noisecharacteristic,L(f)increases
response) but poor sensitivity as
carrier. This means sood sensitiyity far out (limited by the sinx/x
"
compared with the phasedetectormethodclosein'
N
{(,
6 ApproximaleSyslemNoise
!{ -3 Floor of the DelaYLine
=\ DiscrlminalorTechnique
2Z'.
uJ=
.h l-
ICE
Ag
cg
Y! e G,
-r
o
t!t,**;"""G
o
F
1 Hz 10 Hz 100Hz 1 kHz 10 kHz
17
is to lump
A different*.a5.ofesrimatingthe s)'stemnoisefloor of the delal'line discriminatortechnique
all noise contributions into an equivalent phase noise perturbation J02r-tor "rrr' The delal' line
phase noise by a factor of
discriminator.interpreting Jc) as frequency rrbi.u enhancei this equivalent
| /2;f ;.
Example:
= -160 dBc/Hz'
Phase noise of the mixer at i kHz ! t 't kHz'
with a 100 nsec dela5'time the resulting system noise floor is
J2=!t l| i l' ' .
2rf; 'Hz
= -160 dBc + 61 dB = -96 dBc
-100
-90
-80
-70
-60
9 rttl
e, tn -50
Losl *40
Enhancemenlof
-30 equivalentPhasenoise
perturbation delaY
bY I
-20 t,tll=gxl=rl rti
l " r ?( r )g r ( t ) \ 2 ; f ;r
+10
0
100Hz
18
O with Resonator
Discriminator
s.2.3 Frequency
Low Noise
plifier
r'h
t-r[rro,
56(l) for t '*
CavityResonalor
CrystalFiller
Bandwidth . $ I'
Resonator
Inside 1t
ddl o
E q u i va l e n t e l a yT i me r =Eilfo=r[
D
KD= K52;r =*ri}
,?a
=
Jvrms(f) Kdfi rttmsltl
to
Although not a broadbandsolution,it can be advantageous replace the delay line with a cavity
resonatoior crystal filter. Groupdelay td6/du\ produces equivalentr of Q/ rfo for Fourierfrequencies
an
less than half the bandwidth. Inside fo/zq, the systemthereforemeasures the spectraldensity of
frequencynoise*'ith a discriminatorconstant of K6 2Q'/fo.
Bandwidth ' $ t,
Resonator
Outside 1f
=
Jvrms(Q Kd Jdrms(f)
Outside fot}Q,the system ma]' be vieg'ed as 2 signals applied to a phase ddtector u'ith the sideband
noise of one"signalstripped off by the cavity resonator.The system then measuresJd216s with a phase
detectorconstant K6.
19
4 HP Phase Solutions
NoiseMeasurement
o HP 11729C/8662APhaseNoiseTestSystem
(phasedetectormode)
o HP 11729C CarrierNoiseTestSet
mode)
(delayline discriminator
o HP 3047APhaseNoiseMeasurement
System
o HP 11740A PhaseNoise
Microwave
System
Measurement
Following is a comparisonof HP phase noise measurement solutions with particular focus on the
LLTZ1CCarrier NoiseTest Set,HP's most recentcontributionto phasenoisemeasurement.
20
o 4.1 HP 11729C/8662APhaseNoiseTestSystem
Principle Operation
ol
(Phase Method)
Detector
H P 11729CCarrierNoiseTesl Set
r
I
ill*Li Microwave
Source
640 MHz UnderTest
Low Noise
Reference Generation Selection 5- 1280 Hz I
M .01-18 GHz
Signal al
lF-Amp
I
HP 8662A
Synthesized Low Noise
Amp I
SignalGenerator
Opl.003 Speclrum
Analyzer
x0 DC 5-1280 MHz
R
1 0H z - I
EFC FM
Inpul Inpul
1 0M H z
I
I r
I I
,l
I l l Conlroller
I I
I L .J
J
The HP 86624Synthesized signal Generatorprovides astateof'theartlownoieereferenesignalat640MHz
to the Hp 11Z2gC Carrier NoiseTest Set.This signal is appliedto a steprecoverydiodemultiplier which gen-
eratesa combof signals spaced 640MHz ranging beyond18GHz.A switchedin filter selects
by an_appropriate
combline. This microwavireference signal downconverts themicrowavesourceutdertestinto lFrange of 5
an
to 1280MHz.
The doublebalancedmixer phasecompares IF signalwith the outputsignal o{the HP 8662A(.01to 1280
the
MHz). phase quadratureis enforced phaselocking the HP 8662Ato the signal rurdertest either thru the
by
limited electroniccontrol of the HP 8662A's10 MHz crystal oseillator or thnr its DGFM port. The loop band'
widths can be set over a 4 decade range.
A firstorder phaselock loopis enabledbythecapturefeaturemakinglock acquisitioneasy.Then thesecond
orderphaselock loop (with very high dc gain) maintains lock and phasequadr-ature. enablephasenoise
To
-"".u".-.nts within the loop via
Larrd*idth, the phasenoisesuppression be characterized the looptest
can
ports.
21
N
N
HP 11729CCarrierNoiseTest Sel - - --'l
1 r--1 r---1 '
I r 't
i o<---o_n= ^,n*:JOLi r lI
I
Microwavc Sortrco
Undor Tesl
I r+_ 2{- ^"-ilAfj I----1---T--0ri_i8GHr
IHIHH Hi'I"'Tti i(@:- - + - J :I- f I lt+-t llII":::
tfgl^::;-;;; e n e r a t o r
combG cED
(w!E !i,uL
ltooi."ii
PowerAmP L -l- J
l*i
rr-amoV I
I
I 6a0 mHt SAtt lillcr
I 5-1280 MHz
I I
640 MH2 40 dB I
I
I LNA
Inpul
l0 Hr-l
lo"p I '1.5MHr l0 MHzl
resl I HP 3582A/356t4
Loop Conlrol Low Frequency
Speclrum Analyrer
Loop Conlrol Oulpul DC'FM
Aur. OulPul
HP 98364
DG3kTop Compuler
40 MHz Xlal I I
lo MHz Slal osc'
160 MHz sral
640 MHz Low Noise
Relerence Signal
I
I
I
o
0l- 1 2 8 0M H z O r r l P t t l' 0 dBm
I
I
L- o l0 - 20 MHz
I Hz Sleps
| .l Hr SlePs
J
11 NoiseFloorof HP 11729C/8662A Noise
Phase Test
System
04 (PhaseDetector
Method)
I
N
-24
o
o
E -40
\
-60 \ \
I
F \ I
;2in DC FM
tr -80 \ \-86!
tr,
g \ \
E -100 I
\
tr
\
o \ \ rlpicalHpr'rz2eclaeize
o
F 12A
\
\ $ytt"m Noise@ 10 GHz
'
ll\-
llJ 640 MHz ReferenceSignal t-.a
\
L -140 from HP 8662A \
o tl \
z \ -,----
ltJ \_,r
o -160 -- ---
I
o.
o -180
o
@ Hz 1 0H z 1 0 0H z 1 k H z 10 kHz 100kHz MHz 1 0M H z
Oflsetfrom Carrier | [Hz]
Typical Typical Typical Typical
J1 Js ts Ollset 640llHz 320-640 Two-porl Two-porl
/ s y s t e m= 1 0 l o g ( N zr ' l Q r o 1 0 1 0 1 0 1 0 )
- - flom low llHz tun- nolseof noise ol
carrier noise ableE662A HP 11729CH P 1 1 7 2 9 C
N = Multiplicalionnumber of the 640 MHz signal oulput oulput @ 5 G H z @ 10 GHz
/ r = Absolule SSB PhaseNoise of lhe 640 MHz lHz -54 dBc -64 dBc -99 dBc - 9 3 d B c
reference signal (dBclHz). 10Hz -94 dBc -94 dBc -112 dBc -106 dBc
? a = AbsoluteSSB PhaseNoise of lhe 5 lo 640 100H2 -114 rlBc -1ltf dBc -125 dBc - 1 1 9 d B c
(1280)MH: lunable signal (dBc/Hz). 1 kHz -126 dBc -125 dBc -132 dBc - 1 2 6 d B c
,lg = Two-porl noise of HP 11729C(dBc/Hr). 10 kHz -149 dBc -136 d8c -137 dBc - 1 3 1 d B c
100 kHz -159 dBc -136 rlBc -1t18rlBc - 1 4 2 d B c
1 IlHz -159 dBc -146 dBc -153 dBc -147 dBc
For most microwaveapplications,11, the SSB phase noise of the 640 MHz reference signal, is the
dominatingfactorin settingthe noisefloorof the system its phase
as noise multipliedup to microwave
is
frequencies.
23
4.1.2 HP 11729C in
Operating Discriminator
--
Mode
--l
o
Calibration
I
I source f- I
L- t Signalal Carrierlreq. or lF wilh
I Calibrated Sidebands
FM
I
I
I
H P 1 1 7 2 9 C a r r i e rN o t s eT e s l S e t
C
fcalibration
MicrowaveSource
u n d e rT e s t
, Calibralion
b
Comb CombLine I o.o1 18GHz
to
Generalion Section -6'rl i
lF-Amp
ExternalDelay Line
5 l o 1 2 8 0M H z
Baseband
Spectrum
Analyzer
iox.toI
I 'i"l
t_
a Low noisedown convercion microwave
of signalunderlest
a Delaylineoperating lF (5-1500 MHz)
at
o Calibrationsignalprovidedby HP 8662A
o Phase quadrature Indication.
The HP LL729C may also be usedin a delay line discriminator mode.The microwave referencesignal
generatedby the 640MHz signal down convertsthe Bource under test into the IF range.The powersplitter
ind auxiliaiy IF output allows one to simply ineert an appropriate delay line ext*nally.
Delayingt-he signal at IF meanslower delayline losses and alsoa wider choiceof delaydevices, e.g.
like
SAW d;lav line. Any signal generator with FM sidebandsat IF or RF can Eenleas a calibration tool.
24
4.1.3 Sensitivity HP 11729C
of
Mode)
Discriminator
LineFrequency
(Delay
-20
o
o -40
!
1OOns
o t Delay
G -60
cg \ Free'Running
Typical
C) - -y'Source at 10 GHz I
o
o
,9
(!
o -'*r "^J./
usclllalor
at 10GHz
\..'
\ \.\
\\-
o -trof I
z
o
G
3
r
@
o
-,..1- \
\.-
- L.-..-.
o
o
-ruo
L tOOHz 1 kHz 1OkHz lOOkHz 1 MHz 10MHz
1Hz 10Hz
Offset From Carrier(Hz)
PhaseNoiseMeasurement
4.2.1
RF
on Pulsed Signals o
P u l s e d F S o u r c e( D U T )
R
I
I
I
Anti-aliasingFiller
t- J
A
PulseDrive
NarrowBand
PhaseLock LooP
The baseband signal ofa pulsedRF signal phaselocked a reference
to source equalsthe basebandsignal
of a. ut pulsedRf signal jated by the pulseenvelope(seeFig. A, B, C). The CW noisespectrumJ (0 is
multiplied by the envelope function of the pulse,
(-t)n n2'rt
h(t)=
+**3, n
n nt
Sln -It cos -T\
Observed the frequencydomain,this gating process
in meansconvolvingthe two spectrato obtain the
pulsedbasebandsp""tto- (seeFig. C). The resulting spectrumhas J (f) folded around multiples of the
part of this spectrumis yieldedby the DC tcrm of the pulse
iuise repetitionfrequency(PRF).The relevant
enrrelopefunction, it"t.ttshowsthattheleveloftheunpulsedphasenoisespectrum.c(0isreducedbythe
unPursrd
rqu"r.'J the duty cycle.
=
J $1,*o (+)' Jl3por""a
A lowpass filter, the antialiasing filter, with a corner frequency of eliminaie all the aliasing products (SeeFig. D). It also sen'eeto filter any phaeetransients associated
;th lh; pulse modulatoi which otherwise would limit the low noiee amplifier.
ftr. ,vrt"- sensitivity decreaseswith decreasingduty cycle.A sampleand hold circuit in the baseband
iri"en by the puisesignal,wouldimprovetheeystemaensitivityforlowduty cvcle!.Aeimplerway
"ir.uit, systemnoisein the pulse off period is to gate either the LO or the R drive of the mixer'phase
to reduce
deteetor.
-
A side effect of phaselocking to a pulsedRF signal is the reduction of the effectiveloop bandwidth
by t/T, For duty cycles <.:|ttu, becomes
it increasingly important to have a well balancedmixer-phase
detector.
26
Time Domain Frequency omain
D
-+l
PRF zPar
Speclrum PulseEnveloPe
of
FigA: Pulse nvelope
E
t
c
A
c
G
s
F i g B : U n p u l s e dB a s e b a n d i g n a l
S UnpulsedPhaseNoiseSpectrum
(UnPulsed hase P Noise)
l\/l\
t
G
A
g
!ut
!
g
G
pulsed
G
o
-\ ,\ \
-2
Fig C: Pulsed BasebandSignal PulsedPhaseNoiseSpeclrum
beforeLow Pass belore Low Pass
t
G
o
A
E
3
G
a
o
G
a
Fig D: Pulsed Signal
Baseband PulsedPhaseNoiseSpectrum
afler Low Pass aller Low Pass
4.2.2. Pulsed PhaseNoiseMeasurements
(Phase
withthe HP 11729C Detector
Mode)
LPF
HP 11729C
ffi
Noise
Spectrum
Output
640 5 to 1280 PLL Gontrol
Input lnput Voltage
Output
Selectingpulse mode (phasenoise) on the HP 11729Capplies an error cunent to the mixer/phase
detector and switches in a user-suppliedlow pass filter to remove the pulse repetition frequency
feedthrough.
l
4.3 HP 3047APhase System
NoiseMeasurement
ExamPle:
Apptication
Two-por4phase divider
noisemeasurement lrequency
on
HP 3047A Phase Noise llelcurement Syrlem
HP 98il6A or9816A
Derk Top ComPuter
125 Mllz
1 2 5M H z
Comparison
Device t_
The Hp 304?4. phase NoiseMeasurement system represents high sensitivity phasedetectorsystem
a
automatesthe calibration and measurement
with controllableprr"". r""r, circuits. Extensive softwlre
procedures
is.an ^oax-l^ of o residual phasenoise meas
ri--!r^-^ i^ ^- example^f a -acidrrql nhecp noise measure-
Determining the phasenoise of frequencydividers
and the svstemwill measurethe rms sum of
ment. Here,the phasenoiseof the 8662;. i;t;;i;;".J"a
noiseof both dividers.
LrI i lLrL Eri F[rt]F r P L E S ! , i i 5 E t 0l H Z
+tstshr
-3S
-.ig
-59
- E gF
-i6
-BU
-so t- .
- r8g
- ilBF.
-ra6
-t30
-r{8
- l5Ei
-r661-.
-r79
lH=
29
4.4 Phase
Microwave
HP 11740A Noise
System
Measurement
Deviceunder Test
'10.4 Hz
G u n nV C O a l G
HP 11729CCarrierNoise
Tesl Sel HP 3(X7A Spectrum AnalYzerSYslem
HP 9836A or 9815A
Desk Top GomPuler
800 MHz
540 MHz
RelerenceSignal
In the Hp 11?40AMicrowaveNcise Measurement System,the HP ll7290 providesa broadbandand
signal eliminating the needfor a eecond comparable source'
-- noisemicro*'avereference
lo*,
of the HP 11729Cwith either the
The Hp gOaZephasedetectorsystemthen comparesthe IF output
IF eource.
b-12g0 MHz outfut of the HP 8662A or any other suitable and tunable
-\
\l- ---T
-\ --T
''i". ''rl
lek tez< Ir'! reY
. (. ) .dBc./P.z r v's { !:12-l ?er.
:?
30
Iou Comparison SystemSensitivities
of
-20
-40
N l tP 11729C
E C ;AW@\
(, -60
tr t,nz
00ns
l, a\
elay
\
o
G
E
L
o
L
L-
-100
G
o \
o \
o \\ -HP 117:
I -120 t.\ l9c/8662A
0