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Enrico Rubiola – Phase Noise –
1. Introduction 2. Spectra3. Classical variance and Allan variance4. Properties of phase noise5. Laboratory practice6. Calibration7. Bridge (Interferometric) measurements8. Advanced methods9. References
1
www.rubiola.orgyou can download this presentation, an e-book on the Leeson effect, and some other documents
on noise (amplitude and phase) and on precision electronics from my web page
Phase Noise Enrico Rubiola
Dept. LPMO, FEMTOST Institute – Besançon, France email rubiola@femtost.fr or [email protected]
Summary
Enrico Rubiola – Phase Noise –
1 – Introduction
2
Enrico Rubiola – Phase Noise –
Representations of a sinusoid with noise3 introduction – noisy sinusoid
v(t) = V0 [1 + !(t)] cos ["0t + #(t)]
v(t) = V0 cos !0t + nc(t) cos !0t! ns(t) sin!0t
!(t) =nc(t)V0
and "(t) =ns(t)V0
Chapter 1. Basics 2
v(t)
v(t)V0
V0
phase fluctuation!(t) [rad]
phase time (fluct.)x(t) [seconds]
V0/!
2
phase fluctuation
Phasor RepresentationTime Domain
!(t)
ampl. fluct.
V0/!
2
(V0/!
2)"(t)
t
t
amplitude fluctuationV0 "(t) [volts]
normalized ampl. fluct."(t) [adimensional]
Figure 1.1: .
where V0 is the nominal amplitude, and ! the normalized amplitude fluctuation,which is adimensional. The instantaneous frequency is
"(t) =#0
2$+
1
2$
d%(t)
dt(1.3)
This book deals with the measurement of stable signals of the form (1.2), withmain focus on phase, thus frequency and time. This involves several topics,namely:
1. how to describe instability,
2. basic noise mechanisms,
3. high-sensitivity phase-to-voltage and frequency-to-voltage conversionhardware, for measurements,
4. enhanched-sensitivity counter interfaces, for time-domain measurements,
5. accuracy and calibration,
6. the measurement of tiny and elusive instability phenomena,
7. laboratory practice for comfortable low-noise life.
We are mainly concerned with short-term measurements in the frequency do-main. Little place is let to long-term and time domain. Nevertheless, problemsare quite similar, and the background provided should make long-term and timedomain measurement easy to understand.
Stability can only be described in terms of the statistical properties of %(t)and !(t) (or of related quantities), which are random signals. A problem arises
polar coordinates
Cartesian coordinates
|nc(t)|! V0 and |ns(t)|! V0
under low noise approximation It holds that
Enrico Rubiola – Phase Noise –
Noise broadens the spectrum4 introduction – noisy sinusoid
v(t) = V0 [1 + !(t)] cos ["0t + #(t)]
v(t) = V0 cos !0t + nc(t) cos !0t! ns(t) sin!0t
! = 2"#
! ="
2#
Enrico Rubiola – Phase Noise –
Basic problem: how can we measure a low random signal (noise sidebands) close to a strong dazzling carrier?
5 introduction – general problems
s(t) ! hlp(t)
s(t)! r(t" T/4)
convolution(low-pass)
time-domainproduct
vectordifference
distorsiometer,audio-frequency instruments
traditional instruments for phase-noise measurement(saturated mixer)
bridge (interferometric) instruments
Enrico Rubiola – Phase Noise – 6
How can we measure a low random signal (noise sidebands) close to a strong dazzling carrier?
Introduction – general problems
solution(s): suppress the carrier and measure the noise
s(t)! r(t)
Enrico Rubiola – Phase Noise –
Why a spectrum analyzer does not work?
1. too wide IF bandwidth2. noise and instability of the conversion oscillator (VCO)3. detects both AM and PM noise4. insufficient dynamic range
6 introduction – general problems
Some commercial analyzers provide phase noise measurements, yet limited (at least) by the oscillator stability
Enrico Rubiola – Phase Noise –
The Schottky-diode double-balanced mixer saturated at both inputs is the most used phase detector
7 introduction – φ –> v converterEnrico Rubiola – Phase Noise – 4
The Schottky-diode double-balanced mixer saturated at both inputs is the most used phase detector
Introduction – ! ! v converter
s(t) =!
2R0P0 cos [2!"0t + #(t)]
r(t) =!
2R0P0 cos [2!"0t + !/2]
signal
reference
r(t)s(t) = k!!(t) + “2"0” termsproductfiltered
out
The AM noise is rejected by saturationSaturation also account for the phase-to-voltage gain kφ
Enrico Rubiola – Phase Noise –
2 – Spectra
8
Enrico Rubiola – Phase Noise –
Power spectrum density
statistical expectation
In practice, we measure Sv(f) as
This is possible (Wiener-Khinchin theorem) with ergodic processes
Ergodicity: ensemble and time-domain statistics can be interchanged.This is the formalization of the reproducibility of an experiment
In many real-life cases, processes are ergodic and stationary
Stationarity: the statistics is independent of the origin of time.This is the formalization of the repeatability of an experiment
9 Spectra – definitions
In general, the power spectrum density Sv(f) of a random process v(t) is defined as
Sv(f) = E!F
"Rv(t1, t2)
#$
Fourier transformautocorrelation function
E!
·"
F!·"
Rv(t1, t2)
Sv(f) =!!F
"v(t)
#!!2
Enrico Rubiola – Phase Noise –
Physical meaning of the power spectrum density10 Spectra – meaning
P =Sv(f0)
R0
Sv(f0)R0
power in 1 Hz bandwidth dissipated by R0
Enrico Rubiola – Phase Noise –
Physical meaning of the power spectrum density11 Spectra – meaning
The power spectrum density extends the concept of root-mean-square value to the frequency domain
Enrico Rubiola – Phase Noise –
Sφ(f) and ℒ(f) in the presence of (white) noise12 Spectra – Sφ(f) and ℒ(f)
v0+f
v0 v
N
B
SSBP0
!p
!R0P0
!R0NB
L =N
2P0
v0+f
v0 v
N
B
DSBP0
!p
!R0P0
v0–f
B
!R0NB/2
S! =N
P0dBrad2/HzdBc/Hz 3 dB
!rms =!
12
!p =!
NB
2P0!rms =
!12
!p =!
NB
P0
Enrico Rubiola – Phase Noise –
ℒ(f) (re)defined
The problem with this definition is that it does not divide AM noise from PM noise, which yields to ambiguous results
13
The IEEE Std 1139-1999 redefines ℒ(f) as
ℒ(f) = (1/2) × Sφ(f)
ℒ(f) = ( SSB power in 1Hz bandwidth ) / ( carrier power )
Spectra – Sφ(f) and ℒ(f)
The first definition of ℒ(f) was
Engineers (manufacturers even more) like ℒ(f)
Enrico Rubiola – Phase Noise –
y(t) is the fractional frequency fluctuation ν-ν0 normalized to the nominal frequency ν0 (dimensionless)
14 Spectra – useful quantities
Useful quantities
x(t) =1
2!"0#(t)
y(t) =1
2!"0#(t) = x(t)
phase time
fractional frequency fluctuation
x(t) is the phase noise converted into time fluctuationphysical dimension: time (seconds)
y(t) =! ! !0
!0
Enrico Rubiola – Phase Noise –
Power-law and noise processes in oscillators15 Spectra – power lawEnrico Rubiola – Phase Noise – 15
Noise processes in oscillators
Spectra – power-law
Enrico Rubiola – Phase Noise –
Relationships between Sφ(f) and Sy(f)16 Spectra – power law
Enrico Rubiola – Phase Noise –
JitterThe phase fluctuation can be described in terms of a single parameter, either phase jitter or time jitterThe phase noise must be integrated over the bandwidth B of the system (which may be difficult to identify)
The jitter is useful in digital circuits because the bandwidth B is known – lower limit: the inverse propagation time through the system this excludes the low-frequency divergent processes) – upper limit: ~ the inverse switching speed
17 Spectra – jitterEnrico Rubiola – Phase Noise – 17
Jitter
The phase fluctuation can be described in terms of a single parameter, either phase jitter or time jitter
The phase noise must be integrated over the bandwidth B of the system (which may be difficult to identify)
xrms !1
2"#0 $%B S&' f ( df
&rms ! $%B S&' f ( df
The jitter is useful in digital circuits because the bandwidth is known - lower limit: the inverse propagation time through the system
this excludes the low-frequency divergent processes)- upper limit: the inverse witching speed
time jitter phase jitter
converted into time
phase jitter
Victor Reinhardt (invited), A Review of Time Jitter and Digital Systems, Proc. 2005 FCS-PTTI joint meeting
radians
seconds
Enrico Rubiola – Phase Noise –
Typical phase noise of some devices and oscillators
18 Spectra – examples
Phase Noise Metrology 191
function R!(!). The one-side spectrum is preferred because this is whatspectrum analyzers display. Complying to the usual terminology, we use thesymbol " for the frequency and f for the Fourier frequency, i.e. the frequencyof the detected signal when the sidebands around " are down converted tobaseband.
The power-law model is most frequently used for describing phase noise.It assumes that S!(f) is equal to the sum of terms, each of which varies asan integer power of frequency. Thus each term, that corresponds to a noiseprocess, is completely specified by two parameters, namely the exponent andthe value at f = 1 Hz. Five power-law processes, listed underneath, arecommon with electronics.
noise type S!(f)white phase b0f0
flicker phase b!1f!1
white frequency b!2f!2
flicker frequency b!3f!3
random-walk frequency b!4f!4
All these noise types are generally present at the output of oscillators, whiletwo-port devices show white phase and flicker phase noise only. For reference,Fig. 1 reports the typical phase noise of some oscillators and devices.
-200-200-200
S (f
) (
dB
rad /H
z)!
2
-40
-60
-80
-100
-120
-140
-180
-160
0.1 100 100k10k1 10 1k
Fourier frequency (Hz)
10 GHz Dielectric Resonator Oscillator
10 GHz Sapphire Resonator Oscillator (SRO)
10 GHz SRO with noise degenerationRF amplifier
microwave ferrite isolators
100 MHz quartz oscillator
5 MHz quartz osc.
microwave amplifier
Fig. 1. Typical phase noise of some oscillators and devices
Phase noise can be measured by means of a phase-to-voltage converterin conjunction with a spectrum analyzer, which can be of the low frequency
Enrico Rubiola – Phase Noise –
3 – Variances
19
Enrico Rubiola – Phase Noise –
Classical variance
For a given process, the classical variance depends of N
Even worse, if the spectrum is f-1 or steeper,the classical variance diverges
The filter associated to the measure takes in the dc component
20 Variances – classicalEnrico Rubiola – Phase Noise – 20
Classical variance
y !1"0
1#$#
"%t & dt
'2!
1N(1 )
i!1
N
%yi(1N )
j!1
Ny j&
2
normalized reading of a counter that measures (averages) over a time T
classical variance, file of N counter readings
average of the N readings
For a given process, the classical variance depends of N
Even worse, if the spectrum is f-1 or steeper,the classical variance diverges
The filter associated to the measure takes in the dc component
Enrico Rubiola – Phase Noise – 20
Classical variance
y !1"0
1#$#
"%t & dt
'2!
1N(1 )
i!1
N
%yi(1N )
j!1
Ny j&
2
normalized reading of a counter that measures (averages) over a time T
classical variance, file of N counter readings
average of the N readings
For a given process, the classical variance depends of N
Even worse, if the spectrum is f-1 or steeper,the classical variance diverges
The filter associated to the measure takes in the dc component
Enrico Rubiola – Phase Noise –
Zero dead-time two-sample variance(Allan variance)
Definition(Let N = 2, and average)
Estimated Allan variance, file of m counter readings
The filter associated to the difference of two contiguous measures is a band-pass
The estimate converges to the variance
21 Variances – AllanEnrico Rubiola – Phase Noise – 21
Zero dead-time two-sample variance(Allan variance)
Definition(Let N = 2, and average)
Estimated Allan variance, file of m counter readings
The filter associated to the difference of two contiguous measures is a band-pass(about one octave)
The estimate converges to the variance
! y2"
12 #$y2%y1&
2 '
!y2"
12 $m%1& (i"1
m%1
$ y2%y1&2
Enrico Rubiola – Phase Noise – 21
Zero dead-time two-sample variance(Allan variance)
Definition(Let N = 2, and average)
Estimated Allan variance, file of m counter readings
The filter associated to the difference of two contiguous measures is a band-pass(about one octave)
The estimate converges to the variance
! y2"
12 #$y2%y1&
2 '
!y2"
12 $m%1& (i"1
m%1
$ y2%y1&2
Enrico Rubiola – Phase Noise –
The Allan variance is related to the spectrum Sy(f)22 Variances – Allan
Enrico Rubiola – Phase Noise –
Convert Sφ and Sy into Allan variance23 Variances – Allan
noisetype S!(f) Sy(f) S! ! Sy !2
y(") mod!2y(")
whitePM b0 h2f2 h2 =
b0
#20
3fHh2
(2$)2"!2
2$"fH"1
3fH"0h2
(2$)2"!3
flickerPM b!1f!1 h1f h1 =
b!1
#20
[1.038+3 ln(2$fH")]h1
(2$)2"!2 0.084 h1"!2
n"1whiteFM b!2f!2 h0 h0 =
b!2
#20
12h0 "!1 1
4h0 "!1
flickerFM b!3f!3 h!1f
!1 h!1 =b!3
#20
2 ln(2) h!12720
ln(2) h!1
randomwalkFM
b!4f!4 h!2f!2 h!2 =b!4
#20
(2$)2
6h!2" 0.824
(2$)2
6h!2 "
frequency drift y = Dy12
D2y "2 1
2D2
y "2
fH is the high cuto! frequency, needed for the noise power to be finite.
Enrico Rubiola – Phase Noise –
4 – Propertiesof phase noise
24
Enrico Rubiola – Phase Noise –
Ideal synthesizer- noise-free- zero delay time
time translation:output jitter = input jitter phase time xo=xi
linearity of the integral and the derivative operators: φo = (n/d)φi => νo = (n/d)vi
spectra
Frequency synthesis25 Properties of phase noise – synthesis
Enrico Rubiola – Phase Noise – 24
Frequency synthesis
Ideal synthesizer- noise-free- zero delay time
time translation:output jitter = input jitter phase time xo=xi
linearity of the integral and the derivative operators:!o = (n/d)!i => "o = (n/d)"i
spectra
S!o " f # $ " nd #
2
S! i " f #
Properties of phase noise – synthesis
Enrico Rubiola – Phase Noise –
Carrier collapse
random noise =>phase fluctuation
Simple physical meaning, complex mathematics. Easy to understand in the case of sinusoidal phase modulation
26 Properties of phase noise – synthesis
Enrico Rubiola – Phase Noise –
Filtering <=> Phase Locked Loop (PLL)
The PLL low-passfilters the phase
Output voltage: the PLLis a high-pass filter
The signal “2”tracks “1”
The FFT analyzer (notneeded here) can be usedto measure Sφ(f)
27 Properties of phase noise – PLLEnrico Rubiola – Phase Noise – 26
Filtering <=> Phase Locked Loop (PLL)
S!2" f #
S!1" f #$
%ko k!H c" f #%2
4&2 f 2'%ko k! H c" f #%2
Svo" f #
S!1" f #$
4& f 2 k!2
4&2 f 2'%ko k! Hc" f #%2
The PLL low-passfilters the phase
Output voltage: the PLLis a high-pass filter
ko "rad (s (V #
k! "V (rad #
The signal “2”tracks “1”
The FFT analyzer (notneeded here) can be usedto measure S!(f)tracks “1”
Properties of phase noise – PLL
Enrico Rubiola – Phase Noise – 26
Filtering <=> Phase Locked Loop (PLL)
S!2" f #
S!1" f #$
%ko k!H c" f #%2
4&2 f 2'%ko k! H c" f #%2
Svo" f #
S!1" f #$
4& f 2 k!2
4&2 f 2'%ko k! Hc" f #%2
The PLL low-passfilters the phase
Output voltage: the PLLis a high-pass filter
ko "rad (s (V #
k! "V (rad #
The signal “2”tracks “1”
The FFT analyzer (notneeded here) can be usedto measure S!(f)tracks “1”
Properties of phase noise – PLL
Enrico Rubiola – Phase Noise –
For slow frequency fluctuations, a delay-line t is equivalent to a resonatorof merit factor
Frequency discriminator
A resonator turns a slow frequency fluctuation Δν into a phase fluctuation
phase φ
ν0 Qresonator
Parametersν0 resonant frequencyQ merit factor
28
ν0
ν
ν
Properties of phase noise – discriminator
Enrico Rubiola – Phase Noise –
The Leeson effect:phase-to-frequency noise conversion in oscillators
29 Properties of phase noise – Leeson
Enrico Rubiola – The Leeson Effect – 1
The Leeson EffectEnrico Rubiola
Dept. LPMO, FEMTO-ST Institute – Besançon, Francee-mail [email protected] or [email protected]
noise of electronic circuits
oscillator noise
D. B. Leeson, A simple model for feed back oscillator noise, Proc. IEEE 54(2):329 (Feb 1966)
S!" f #
f
Leesoneffect
resonator
out
fL = !0/2Q
S! " f # $ %1&" '0
2Q #2
1f 2 ( S) " f #
oscillatornoise
amplinoise
www.rubiola.orgsome free documents on noise (amplitude and phase) and on
precision electronics will be available in this non-commercial site
D. B. Leeson, A simple model for feed back oscillator noise, Proc. IEEE 54(2):329 (Feb 1966)
E. Rubiola, The Leeson effect, Tutorial 2A, Proc. 2005 FCS-PTTI (tutorials)E. Rubiola, The Leeson effect, e-book, (http://arxiv.org/abs/physics/0502143 or rubiola.org)
Enrico Rubiola – Phase Noise –
5 – Laboratory practice
30
Enrico Rubiola – Phase Noise –
Practical limitations of the double-balanced mixer
1 – Power narrow power range: ±5 dB around Pnom = 5-10 dBm r(t) and s(t) should have (about) the same power
2 – Flicker noise due to the mixer internal diodes typical Sφ = –140 dBrad2/Hz at 1 Hz in average-good conditions
3 – Low gain kφ ~ –10 to –14 dBV/rad typical (0.2-0.3 V/rad)
4 – White noise due to the operational amplifier
31 Laboratory practice – background noise
Enrico Rubiola – Phase Noise –
Typical background noise
RF mixer (5-10) MHzGood operating conditions (10 dBm each input)Low-noise preamplifier (1 nV/√Hz)
32 Laboratory practice – background noise
Enrico Rubiola – Phase Noise –
The operational amplifier is often misused
Warning: if only one arm of the power supply is disconnected, the LT1028 may delivers a current from the input (I killed a $2k mixer in this way!)
You may duplicate the low-noise amplifier designed at the FEMTO-STRubiola, Lardet-Vieudrin, Rev. Scientific Instruments 75(5) pp. 1323-1326, May 2004
33 Laboratory practice – background noise
Enrico Rubiola – Phase Noise –
A proper mechanical assembly is vital34 Laboratory practice – background noise
Enrico Rubiola – Phase Noise – 35 Laboratory practice – useful schemesEnrico Rubiola – Phase Noise – 34 Laboratory practice – useful schemes
Two-port device under test (DUT)
Enrico Rubiola – Phase Noise – 36 Laboratory practice – useful schemes
Two-port device under test (DUT)Enrico Rubiola – Phase Noise – 35 Laboratory practice – useful schemes
other configurations are possible
Enrico Rubiola – Phase Noise –
A frequency discriminator can be used to measure the phase noise of an oscillator
37 Laboratory practice – useful schemes
Enrico Rubiola – Phase Noise –
Phase Locked Loop (PLL)
Phase: the PLLis a low-pass filter
Output voltage: the PLLis a high-pass filter
compare an oscillator under test to a reference low-noise oscillator– or –
compare two equal oscillators and divide the spectrum by 2 (take away 3 dB)
38 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise – 26
Filtering <=> Phase Locked Loop (PLL)
S!2" f #
S!1" f #$
%ko k!H c" f #%2
4&2 f 2'%ko k! H c" f #%2
Svo" f #
S!1" f #$
4& f 2 k!2
4&2 f 2'%ko k! Hc" f #%2
The PLL low-passfilters the phase
Output voltage: the PLLis a high-pass filter
ko "rad (s (V #
k! "V (rad #
The signal “2”tracks “1”
The FFT analyzer (notneeded here) can be usedto measure S!(f)tracks “1”
Properties of phase noise – PLL
Enrico Rubiola – Phase Noise – 26
Filtering <=> Phase Locked Loop (PLL)
S!2" f #
S!1" f #$
%ko k!H c" f #%2
4&2 f 2'%ko k! H c" f #%2
Svo" f #
S!1" f #$
4& f 2 k!2
4&2 f 2'%ko k! Hc" f #%2
The PLL low-passfilters the phase
Output voltage: the PLLis a high-pass filter
ko "rad (s (V #
k! "V (rad #
The signal “2”tracks “1”
The FFT analyzer (notneeded here) can be usedto measure S!(f)tracks “1”
Properties of phase noise – PLL
Enrico Rubiola – Phase Noise – 39 Laboratory practice – oscillator measurement
Phase Locked Loop (PLL)Enrico Rubiola – Phase Noise – 38 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise – 40 Laboratory practice – oscillator measurement
A tight PLL shows many advantagesEnrico Rubiola – Phase Noise – 39 Laboratory practice – oscillator measurement
but you have to correct the spectrum for the PLL transfer function
Enrico Rubiola – Phase Noise –
Practical measurement of Sφ(f) with a PLL
1. Set the circuit for proper electrical operationa. power level
b. lock condition (there is no beat note at the mixer out)
c. zero dc error at the mixer output (a small V can be tolerated)
2. Choose the appropriate time constant
3. Measure the oscillator noise
4. At end, measure the background noise
41 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise – 42 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise – 41 Laboratory practice – oscillator measurement Warning: a PLL may not be what it seems
Enrico Rubiola – Phase Noise –
PLL – two frequencies
At low Fourier frequencies, the synthesizer noise is lower thanthe oscillator noise
At higher Fourier frequencies, the white and flicker of phase of the synthesizer may dominate
The output frequency of the two oscillators is not the same. A synthesizer (or two synth.) is necessary to match the frequencies
43 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise –
PLL – low noise microwave oscillators
Due to the lower carrier frequency, the noise of a VHF synthesizer is lower than the noise of a microwave synthesizer.
With low-noise microwave oscillators (like whispering gallery) the noise of a microwave synthesizer at the oscillator output can not be tolerated.
This scheme is useful• with narrow tuning-range oscillator, which can not work at the same freq.• to prevent injection locking due to microwave leakage
44 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise –
Designing your own instrument is simpleStandard commercial parts:• double balanced mixer• low-noise op-amp• standard low-noise dc components in the feedback path• commercial FFT analyzer
Afterwards, you will appreciate more the commercial instruments:– assembly– instruction manual– computer interface and software
45 Laboratory practice – oscillator measurement
Enrico Rubiola – Phase Noise –
6 – Calibration
46
Enrico Rubiola – Phase Noise –
Calibration – general procedure1 – adjust for proper operation: driving power and quadrature
2 – measure the mixer gain kφ (volts/rad) —> next
3 – measure the residual noise of the instrument
47 Calibration – general
Enrico Rubiola – Phase Noise –
Calibration – general procedure4 – measure the rejection of the oscillator noise
Make sure that the power and the quadrature are the same during all the calibration process
48 Calibration – general
Enrico Rubiola – Phase Noise –
Calibration – measurement of kφ (phase mod.)
The reference signal can be a tone: detect with the FFT, with a dual-channel FFT, or with a lock-in (pseudo-)random white noise
tone:
white noise
Some FFTs have a white noise outputDual-channel FFTs calculate the transfer function |H(f)|2=SVm/SVd
49 Calibration – measurement of kφ
Vm
Enrico Rubiola – Phase Noise –
Calibration – measurement of kφ (rf signal)50 Calibration – measurement of kφ
Enrico Rubiola – Phase Noise –
Calibration – measurement of kφ (rf noise)A reference rf noise is injected in the DUT path
through a directional coupler
51 Calibration – measurement of kφ
Enrico Rubiola – Phase Noise –
7 – Bridge (interferometric) measurements
52
Enrico Rubiola – Phase Noise – 53 Bridge – Wheatstone
Wheatstone bridgeEnrico Rubiola – Phase Noise – 52 Interferometer – Wheatstone bridge
Enrico Rubiola – Phase Noise –
Wheatstone bridge – ac version
equilibrium: Vd = 0 –> carrier suppression
static error δZ1 –> some residual carrier real δZ1 => in-phase residual carrier Vre cos(ω0t) imaginary δZ1 => quadrature residual carrier Vim sin(ω0t)
fluctuating error δZ1 => noise sidebands real δZ1 => AM noise nc(t) cos(ω0t) imaginary δZ1 => PM noise –ns(t) sin(ω0t)
54 Bridge – Wheatstone
Enrico Rubiola – Phase Noise – 55 Bridge – Wheatstone
Wheatstone bridge – ac versionEnrico Rubiola – Phase Noise – 54 Interferometer – Wheatstone bridge
Enrico Rubiola – Phase Noise – 56 Bridge – schemeEnrico Rubiola – Phase Noise – 55 Interferometer – scheme
Bridge (interferometric) phase-noise and amplitude-noise measurement
Enrico Rubiola – Phase Noise – 57 Bridge – synchronous detection
Synchronous detectionEnrico Rubiola – Phase Noise – 56 Interferometer – synchronous detection
Enrico Rubiola – Phase Noise –
Synchronous in-phase and quadrature detection58 Bridge – synchronous detection
Enrico Rubiola – Phase Noise – 57
Synchronous in-phase and quadrature detection
Interferometer – synchronous detection
Enrico Rubiola – Phase Noise – 59 Bridge – background noise
White noise floorEnrico Rubiola – Phase Noise – 58 Interferometer – noise floor
Enrico Rubiola – Phase Noise –
White noise floor – example
60 Bridge – background noiseEnrico Rubiola – Phase Noise – 59 Interferometer – noise floor
White noise floor – example
Enrico Rubiola – Phase Noise –
What really matters (1)61 Bridge – summary
Enrico Rubiola – Phase Noise –
What really matters (2)62 Bridge – summary
Enrico Rubiola – Phase Noise –
A bridge (interferometric) instrument can be built around a commercial instrument
You will appreciate the computer interface and the software ready for use
63 Bridge – commercial
Enrico Rubiola – Phase Noise –
8 – Advanced Techniques
64
Enrico Rubiola – Phase Noise – 65 Advanced – flicker reduction
Low-flicker schemeEnrico Rubiola – Phase Noise – 64 Advanced – flicker reduction
Enrico Rubiola – Phase Noise – 66 Advanced – flicker reduction
Interpolation is necessaryEnrico Rubiola – Phase Noise – 65 Advanced – flicker reduction
Enrico Rubiola – Phase Noise –
Correlation can be used to reject the mixer noise
67 Advanced – correlation
Enrico Rubiola – Phase Noise –
Correlation – how it works
68 Advanced – correlation
Enrico Rubiola – Phase Noise –
Flicker reduction, correlation, and closed-loop carrier suppression can be combined
E. Rubiola, V. Giordano, Rev. Scientific Instruments 73(6) pp.2445-2457, June 2002
69 Advanced – matrix
dualintegr matrix
D
R0=
50Ω
matrixB
matrixGv2
w1
w2
matrixB
matrixG
w1
w2
FFTanalyz.
atten
atten
x t( )
Q
II−Q
modul
’ γ’atten
Q
II−Q
detectRF
LO
Q
II−Q
detectRF
LOg ~ 40dB
g ~ 40dB
v1
v2
v1
u1
u2 z2
z1
atten
DUT
γΔ’
0R
0R
10−20dBcoupl.
pow
er sp
litte
r
pump
channel a
channel b (optional)
rf virtual gndnull Re & Im
RF
suppression controlmanual carr. suppr.
pump LO
diagonaliz.
readout
readout
arbitrary phase
var. att. & phase
automatic carrier
arbitrary phase pump
I−Q detector/modulator
G: Gram Schmidt orthonormalizationB: frame rotation
inner interferometerCP1 CP2
CP3
CP4
−90° 0°
I
QRF
LO
Enrico Rubiola – Phase Noise – 70 Advanced – comparison
1 10 32 4 5
−180
10 10 10
−140
−170
−160interferometer
correl. saturated mixer
Fourier frequency, Hz−220
−210
saturated mixer
correl. sat. mix.
double interf.
interferometer
residual flicker, by−step interferometer
residual flicker, fixed interferometer
residual flicker, fixed interferometer
residual flicker, fixed interferometer, ±45° detection
S (f) dBrad2/Hzϕ real−time
correl. & avg.
nested interferometer
mixer, interferometer
saturated mixer
double interferometer
−200
−190
10
−150
measured floor, m=32k
Comparison of the background noise
Enrico Rubiola – Phase Noise –
9 – ReferencesSTANDARDSJ. R. Vig, IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology--Random Instabilities, IEEE Standard 1139-1999 ARTICLESJ. Rutman, Characterization of Phase and Frequency Instabilities in Precision Frequency Sources: Fifteen Years of Progress, Proc. IEEE vol.66 no.9 pp.1048-1075, Sept. 1978. RecommandedE. Rubiola, V. Giordano, Advanced Interferometric Phase and Amplitude Noise Measurements, Rev. of Scientific Instruments vol.73 no.6 pp.2445-2457, June 2002. Interferometers, low-flicker methods, correlation, coordinate transformation, calibration strategies, advanced experimental techniquesBOOKSChronos, Frequency Measurement and Control, Chapman and Hall, London 1994. Good and simple reference, although datedW. P. Robins, Phase Noise in Signal Sources, Peter Peregrinus,1984. Specific on phase noise, but dated. Unusual notation, sometimes difficult to read.Oran E. Brigham, The Fast Fourier Transform and its Applications, Prentice-Hall 1988. A must on the subject, most PM noise measurements make use of the FFTW. D. Davenport, Jr., W. L."Root, An Introduction to Random Signals and Noise, McGraw Hill 1958. Reprinted by the IEEE Press, 1987. One of the best references on electrical noise in general and on its mathematical properties.E. Rubiola, The Leeson effect (e-book, 117 pages, 50 figures) arxiv.org, document arXiv:physics/0502143E. Rubiola, Phase Noise Metrology, book in preparation
ACKNOWLEDGEMENTSI wish to express my gratitude to the colleagues of the FEMTO-ST (formerly LPMO), Besancon, France, firsts of which Vincent Giordano and Jacques Groslambert for a long lasting collaboration that helped me to develop these ideas and to put them in the present form.
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