FP 420 BPM Workshop Signal Processing for BPMs Marek GASIOR CERN-AB-BI
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Transcript of FP 420 BPM Workshop Signal Processing for BPMs Marek GASIOR CERN-AB-BI
FP 420 BPM Workshop 1M. Gasior, CERN-AB-BI
FP 420 BPM Workshop
Signal Processing for BPMs
Marek GASIOR
CERN-AB-BI
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Comparison among signals processing Comparison among signals processing for BPMfor BPM
G. Vismara G. Vismara
Introduction Introduction
Signal analysisSignal analysis
Design parametersDesign parameters
System familiesSystem families
System descriptionsSystem descriptions
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IntroductionIntroduction
Very large evolution since early days Processing choice depends on machine
parameters No unique solution Wide range of signal processing:
Individual
Multiplexed (MPX)
Difference-over-Sum ()
Normalization (Phase & Time)
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Signal analysisSignal analysis
Beam currentIb = [Qb*Nb]/trev
Qb = charge/bunch, Nb = number of bunches, trev = revolution period
Ib or Qb ? Ib measurements over several revolution cycles
Qb measurements on individual bunches
Induced signalV (t) = Zt*Ib (t) Zt is the PU’s transfer impedance
Bunch shape: (longitudinal charge density) Gaussian for leptons, (Cosine)2 for protons
Bunching factor: BF = (Bunching period)/(Bunch widthfwhm)
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Beam structure (rf bucket filling)Beam structure (rf bucket filling)
Un-bunched beam Un-structure beam. No rf (Protons & Heavy Ions machines).
Very difficult to be treated. All
Beam bunches in all rf bucket. Optimized for maximum Ib
(SPS) The easiest to be treated. Almost monochromatic freq.spectrum
Few Beam bunches in few rf bucket with longitudinal symmetry.
The highest bunch density (LEP). Variable
Particular structure (no longitudinal symmetry); it includes single bunch filling and single passage (transfer lines)
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Beam structuresBeam structures
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Signal processing methodsSignal processing methods
The beam positionbeam position is uniquely related to the amplitude ratioamplitude ratio of the induced signals on opposite electrodes.
Processing methods for position calculation:
Difference over Sum () Analog and Digital process
Amplitude to phase/ time Passive analog process
Log-ratio (logA-logB) Active analog process
Transfer Function
-1
-0.5
0
0.5
1
-1 -0.5 0 0.5 1
Normalized
Position (U)
Computed
Position (U)
D/ SAtn(a/ b)loga-logb
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Reference parameterReference parameter
Position = Kx,y* (A-B)/(A+B) = Kx,y*Np
Kx,y = scaling factor; A, B = induced signals; Np = Normalized
Position
Np is dimensionless and varies between 1U passing through 0 for a
centered beam. 1U is the “Normalized half aperture” Na
The “Normalized half apertureNormalized half aperture”” should be the reference parameter when specifying a processing system.
This will make possible comparisons among systems
r = Kx,y
A -1U B 1U
D
C
0
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The ability to minimize the beam position errors Error sources:
mechanic, magnetic and electronics causes The offset for a centered beam should be minimized
Beam based alignment techniques Electronics error sources:
Impedance mismatching on interconnecting cables Electromagnetic interference and noise on the
input stage Non-linearity and beam intensity dependence Channels gain differences and calibration errors Digitizer granularity
Parameters: AccuracyParameters: Accuracy
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Parameters: ResolutionParameters: Resolution
Important in colliding machines for luminosity Minimum position difference that can be resolved
Single shot: Stdev of individual measurements referred to the
normalized aperture Averaged:
as above but integrated over several revolutions Limiting factors:
At low level, it depends on the input noise and the BW For large signals, on the ADC resolution and the time
jitter State of art resolutions :
Single shot: < 0.02% of Na (few micron)
Averaged : < 20 ppm of Na (sub-micron)
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Parameters: StabilityParameters: Stability
The measurement’s uncertainty will affect the global resolution of system.
The position measurements should be independent of the beam intensity, the bunch shaping and the rate. They should be stable vs. temperature and time, at least during the time interval between two calibrations
Stability versus input signalStdev from a series of digitized positions measured over the whole dynamic range.
Position temperature coefficientSlope of the position drift versus temperature
Long term position stabilityStdev of a series of digitized positions versus time
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Parameters: Sensitivity & DynamicParameters: Sensitivity & Dynamic
Sensitivity: The minimum input level at which a beam position measurement
still fulfills the accuracy specifications (> 107 p/b) Dynamic
It determines the capability of the system to absorb very different beam intensities conditions
It’s defined as the difference, expressed in dB, between the maximum input level before a large non-linearity on the output signal appears (saturation) and the minimum input level at which a pre-defined signal to noise ratio (S/N) is reached
Processors using a discrimination level will not be limited by the S/N ratio, the lower limit being determined by the discriminator's threshold.
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Parameters: Acquisition timeParameters: Acquisition time
The time required for the signal processor to store a full set of data into the memory
The importance of this parameter is related to the capability of resolving individual bunches and the absolute resolution of the processor
Several elements contribute to build-up this time: The LP and BP filters The switching and acquisition time (MPX processors) The PLL’s time to synchronize (synchronous detector) The AGC’s set-up time (constant sum) The S&H circuit and the ADC’s conversion time
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Processing system familiesProcessing system families
Advantages Weakness
Large Bandwidth Limited dynamic
Long term stability No turn by turn
Center stability Gain switching
Amplitude No intensity independent information
Multiplexed
Individual
PassiveNormalization
ElectrodesA, B
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No intensity information Reduced N°of digitizing
bit
Advantages Weakness
Long term stability Gain matching
Large dynamic Limited linearity
Large Bandwidth Time matching
Simplicity Phase matching
Processing system familiesProcessing system families
ConstantSum
Amplitude
to phase
Amplitude
to time
Logarithmic conversion
Normalizers
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Processing system familiesProcessing system families
Definition Types
Individual bunches - Track & Hold separated by >10 ns - Log amplifiers to single - Amp to Time Normalizer
Turn-by-turn - Heterodyne
or individual bunches - Amplitude to separated by >100 ns Phase normalizer
Non consecutive - MPX turns measurements
WideBand
NarrowBand
SlowAcquisitio
n
Acquisition
Time
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Processing system familiesProcessing system families
Legend: / Single channel
Wide Band
Narrow band
Normalizer
Processor
ActiveCircuitr
y
Heterodyne POS = (A-B) Synchronou
sDetection
AGCon
MPX
ElectrodesA, B
PassiveNormaliz.
POS = [log(A/B)] = [log(A)-log(B)]
DifferentialAmplifier
Logarithm. Amplifiers
IndividualTreatment
Limiter,t to Ampl.
Amp.to Time POS = [A/B]
POS = [ATN(A/B)] Amp.
to Phase
.Limiter, to Ampl.
POS = HeterodyneHybrid
HomodyneDetection
POS = or = (A-B)/(A+B)
Sample,Track,Integr. & Hold
Switch. gain
Amplifier
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MPX schematicsMPX schematics
MPXPre-Ampl
Active
Matrix
A
B
C
D
X
Y
AGC
BPFilter
BPFilter
VCOPLLLimiter
BPFilterIF.
AmplMixer
VLSI
Freq.Synt.
Mixer
MPX
A
B
C
D
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MPX descriptionMPX description Conceived for closed orbit of stable stored beams
The input signals are sequentially multiplexed into a single receiver
Multi-stage configuration of GaAs switches (Channels isolation >50 dB)
A BP filter selects the largest line of the spectrum
Pre-amplifier with AGC. Large input dynamic (>80 dB) and gain control (>50 dB) Noise Figure difficult to optimize.
Active mixer, driven by a frequency synthesizer, down convert to standard IF
IF amplifier with AGC and synchronous detection, by comparing the phase of a sample of carrier signal with a reference signal via a VCO in a phase lock loop (VLSI)
BP filter to suppress side-bands (100 kHz > BW< 1MHz).
De-multiplexer, Track & Hold and active matrix produce 7 signals (A, B, C, D, Sum, X, Y) store theirs values in four analog memories
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Reduced number of channels (x4)
Identical gain for all the channels
No need for gain selection (AGC)
Large dynamic range (>80dB)
Excellent position stability
No temperature dependence and components aging.
Reduced N° of bits at equivalent resolution (Normalization)
MPX performancesMPX performances
Stable beam during the scanning
No turn by turn acquisition
Slow acquisition rate (MPX)
Reduced Noise Figure (front end matching & MPX insertion losses, AGC pre-ampli.)
Reduced linearity, for non-linear PU’s since the is not constant
Large engineering
No intensity information (AGC)
Advantages Limitations
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LPFilter
LPFilter
A
B
0° 0°
180°0°
Pre-Ampl
Pre-Ampl
Sample& Hold
Sample& Hold
Wide band processing
Difference over Sum (Difference over Sum () )
BPFilter
BPFilter
A
B0°
0°0°
180°
Sample& Hold
Sample& Hold
Narrow band processingMixer
Mixer
PreAmpl
PreAmpl
Limiter
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Difference over Sum (Difference over Sum () description) description
The and signals are obtained from a passive four port 180° hybrid
Wide-bandIt offers wide-band response (from kHz to GHz over >3 decades), very
large dynamic only limited by the electronics, isolation among ports (>30 dB)
Programmable gain amplifiers (Ga As switches) and track or peak & hold circuits
Wide bunches may be directly digitized by FADC (>1 GS/s)A & B signals can be treated separately by suppressing the 180° hybrid
Narrow-band BP filters are used to select the largest line in the spectrum. Programmable gain amplifiers and homodyne detector (a fraction of
signal is limited and used as local oscillator). Track & Hold and an externally triggered ADCs, digitize the
andsignals
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Difference over Sum ( Difference over Sum ( ) ) performancesperformances
[W.B.] & {N.B.}
The central position independent on input intensity.
Intensity measurement available
Excellent Noise Figure
[Wide band allows measurements on multiple bunches (t <20 ns)]
{ Large dynamic > 90 dB}
Programmable gain amplifiers
Multiple calibration coefficients
The absolute position is f(gain)
{Tight phase matching(at all the gainsrequired by the synchronous detection (5°) }
{ Pedestal error on }
LimitationsAdvantages
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LPFilter
LPFilter
A
B
LogampI to V
Converter
Diff.Ampli
Position = K * VoutLogamp
I to VConverter
Logarithmic amplifier schematicsLogarithmic amplifier schematics
Each signal is compressed by a logarithmic amplifier, filtered and applied to a differential amplifier.
The position response is Pos. [log(A/B)] = [log(A)-log(B)]
(Vout) where Vout is the voltage difference between the log-amplifiers outputs
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10 dB
Full-waveDetector
Ampli-limiter
+Out-
+Log. Out -
+I n-
10 dB
Full-waveDetector
Ampli-limiter
10 dB
Full-waveDetector
Ampli-limiter
10 dB
Full-waveDetector
Ampli-limiter
10 dB
Full-waveDetector
Ampli-limiter-80 -60 -40 -20 0 dBm
.4
.8
1.2
1.6
2.0
0
1.0
-1.0
2.0
-2.0
dB
V
Logarithmic amplifier descriptionLogarithmic amplifier description
New generation circuits use several cascaded limiting amplifiers, with fix gain and wide bandwidth. Full wave rms detectors are applied among each stage and by summing theirs output signals, a good approximation to a logarithmic transfer function is obtained. Typical parameters are:
Input dynamic range : >90 dB Input noise: < 1.5 nV/Hz Non conformance lin.: < 0.3 dB Limiter Bandwidth: D.C. to >2 GHz Video Bandwidth: D.C. to 30 MHz
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Logarithmic amplifiers performancesLogarithmic amplifiers performances
Possible applications in the time and frequency domain (NB & WB)
Very large dynamic range (>90 dB) without gain adjustment
Wide input bandwidth No bunch shape dependency Simultaneous digitization of
individual + and - charges Auto-triggering capability Simple engineering
State of art performances are not simultaneously available
Poor position stability vs.. input level, for particular conditions
Limited linearity ( few % of the normalized aperture)
Limited long term stability Temperature dependence
LimitationsAdvantages
BI Review - Rhodri Jones (CERN - SL/BI)
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INPUT OUTPUT
A A
BB
T1 = 1.5 ns
T1 = 1.5 ns
The Front-End Electronics
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-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Time [ns]
Am
plitu
de A
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Am
plitu
de B
1.5ns
A
B
B + 1.5ns
A + (B + 1.5ns)A B
Beam
The Wide Band Time Normaliser
BI Review - Rhodri Jones (CERN - SL/BI)
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-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Time [ns]
Am
plitu
de A
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Am
plitu
de B
1.5ns
A
B
A + 1.5ns
B + (A + 1.5ns)
A + (B + 1.5ns)A B
The Wide Band Time Normaliser
t depends on position
BI Review - Rhodri Jones (CERN - SL/BI)
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-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Time [ns]
Am
plitu
de A
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Am
plitu
de B
A B
A+(B+1.5ns)
B+(A+1.5ns)+10ns
System output
The Wide Band Time Normaliser
Interval = 10 1.5ns
BI Review - Rhodri Jones (CERN - SL/BI)
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The Wide Band Time Normaliser
CAL. and TESTGENERATOR ADC
LOWPASS
FILTER
CALIBRATOR
PICK-UP
50 CABLE
Intensity
Measurement
Trigger
AutoTrigger
50 CABLE
LOWPASS
FILTERCALIBRATOR
NORMALISER INTEGRATOROPTICAL
LINK
TUNNEL SURFACE
DAB
BI Review - Rhodri Jones (CERN - SL/BI)
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-5%
-4%
-3%
-2%
-1%
0%
1%
2%
3%
4%
5%
1E+08 1E+09 1E+10 1E+11 1E+12
Number of Charges per Bunch
Per
cent
age
Err
or w
.r.t.
Hal
f Rad
ius
[%]
Linearity - High SensitivityLinearity - Low SensitivityNoise - High SensitivityNoise - Low sensitivity
Pilot Nominal Ultimate
WBTN - Linearity v IntensityFor LHC Arc BPMs 1% ~ 130m
BI Review - Rhodri Jones (CERN - SL/BI)
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WBTN - Linearity v Position
-8%
-6%
-4%
-2%
0%
2%
4%
6%
8%
-1 -0.5 0 0.5 1
Normalised Position
Per
cent
age
Err
or w
.r.t.
Hal
f Rad
ius
[%]
Calibration Point
Measured Value
Calibrated Value
Linearised Value
For LHC Arc BPMs 1% ~ 130m
BI Review - Rhodri Jones (CERN - SL/BI)
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Accuracy and ResolutionBunch Type Pilot Bunch Bunches of Nominal IntensityMode of Operation Trajectory
(singleshot)
Orbit(224 turnaverage)
Trajectory(single shot,
single bunch)
Trajectory(single shot,
average of allbunches)
Orbit(average of all
bunches over 224turns)
Resolution(rms) 200m 20m 50m 5m 5m
EL
EC
TR
ON
ICS
Accuracy(rms) 150m
AlignmentError (rms) 200m
ME
CH
AN
ICA
L
Residual afterk-modulation
(rms)<50m
3 = 750m20% of 4mmClosed Orbit ‘budget’(Spec = 500m)
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Amplitude to Time Normalizer Amplitude to Time Normalizer performancesperformances
Reduced number of channels (x2)
No need for gain selection Input dynamic > 50 dB Signal dynamic independent on
the number of bunches ~10 dB compression of the
position dynamic (recombination)
Acquisition rate > 40 MS/s Auto-trigger Reduced N° of bits at
equivalent resolution (Normalization)
Mainly reserved to bunched beams
Tight time adjustment Propagation delay stability and
switching time uncertainty are the limiting performance factors
No Intensity information
Remark: A specifically designed monolithic Ga-As chip will allow for a large speed breakthrough
LimitationsAdvantages
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a
b
2nd analogfrequencytranslator
2nd analogfrequencytranslator
Evolution of radio systems: as processing and sampling technologies improve,digital moves from the baseband end (a) towards the pick-up sensor (b).
Pick-up or sensorSupplying rf signal
Analogdemodulatorand filter
Digitalfrequencytranslator
Digitaldemodulatorand filter
Digital signal
processor(DSP)
output
outputADC
ADC1st analog frequencytranslator
Analogfrequencytranslator
AnalogDigital
Digital receiver (basic)Digital receiver (basic)
Digital receiver is a new approach of the heterodyne receiver
The basic functionality is preserved but implemented differently
Present situation allows to place the digital transition just after the IF amplifier
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Programmability
Narrow and wide band processing
Identical gain for all the channels due to possible permanent calibration
Resolution may be improved by over-sampling techniques
Excellent linearity (ADC)
Large dynamic range (AGC)
Reduced N° of bits at equivalent resolution (Normalization)
Digital Receiver performancesDigital Receiver performances
No single shot measurement
No “plug and play” system
Large engineering
All problems related to a new un-experienced processing system
The present advantages alone do not justify the man power investment, but I consider this technique as one of the most promising for the future
LimitationsAdvantages
FP 420 BPM Workshop 39M. Gasior, CERN-AB-BI
Conclusions for FP 420 BPMs
No obvious solution to satisfy all FP 420 BPM requirements, especially
– Required „normalized accuracy” in the order of 10 um / 100 mm, i.e. 10-4
– Bunch by bunch measurement
Already „bunch by bunch” resolution in the order of 10-4 is difficult to achieve
Propositions
– Measurement with a single multiplexed channel for a few bunches
– Something special, which employs specific features of the FP 420 BPM system
What can help to relax the difficult requirements?
– Required accuracy concerns relative distance beam – SI detector
– Required measurement range is much smaller than the vacuum chamber diameter
FP 420 BPM Workshop 40M. Gasior, CERN-AB-BI
An idea of a PU with reduced „working aperture”
jaw 1 jaw 2
electrode 1signal
electrode 2signal
optical measurementof relative jaw position
Sidetector
A „collimator arrangement” to reduce the PU „working aperture”
If the jaw distance can be reduced to some 10 mm, then the „normalized accuracy” drops to 10-3, which is much more reasonable
One PU electrode on one unit with the Si detector, giving excellent relative positioning
Jaw relative position measured with optical means
Possible dynamic jaw positioning with respect to the beam
Some know-how could be quickly transferred from the collimator people, especially if they could think about using a similar idea for the collimator system
FP 420 BPM Workshop 41M. Gasior, CERN-AB-BI
A version more robust for scattered particles
ima
ge
be
am
probe 1signal
probe 2signal
This version may be also interesting for collimators, for symmetric jaw positioning with respect to the beam
Signal quality not very demanding for simple signal equalization from both probes
FP 420 BPM Workshop 42M. Gasior, CERN-AB-BI
Spare slides
FP 420 BPM Workshop 43M. Gasior, CERN-AB-BI
Wall Current Monitor (WCM) principle
The BEAMBEAM current is accompanied by its IMAGEIMAGE A voltage proportional to the beam current develops on the RESISTORSRESISTORS in the beam pipe gap The gap must be closed by a box to avoid floating sections of the beam pipe The box is filled with the FERRITEFERRITE to force the image current to go over the resistors The ferrite works up to a given frequency and lower frequency components flow over the box wall
FP 420 BPM Workshop 44M. Gasior, CERN-AB-BI
WCM as a Beam Position Monitor
For a centered BEAMBEAM the IMAGEIMAGE current is evenly distributed on the circumference The image current distribution on the circumference changes with the beam position Intensity signal () = resistor voltages summed Position dependent signal () = voltages from opposite resistors subtracted The signal is also proportional to the intensity, so the position is calculated according to / Low cut-offs depend on the gap resistance and box wall (for ) and the pipe wall (for ) inductances
LR
fL π2
L
RfL π2
FP 420 BPM Workshop 45M. Gasior, CERN-AB-BI
A new design: Inductive Pick-Up (IPU)
An eight electrode “tight” design to avoid resonances in the GHz range
The electrodes cover 75 % of the circumference
The electrode internal diameter is only 9 mm larger then the vacuum chamber of 40 mm and it is occupied by the ceramic insertion (alumina)
The transformers are as small as possible to gain high frequency cut-off with many turns
The transformers are mounted on a PCB
The connection between the electrodes and the cover is made by screws
Electrode diameter step is occupied by the ceramic tube
The tube is titanium coated on the inside
FP 420 BPM Workshop 46M. Gasior, CERN-AB-BI
Active Hybrid Circuit – Performance
The CMRR at 100 MHz is as high as 55 dB (datasheet 42 dB)
The CMRR for frequencies below 10 MHz is limited by the measurement setup
signal high cut-off frequency about 200 MHz
2 3 5 2 3 5 2 3 5 2 3 5
F re q u en cy [H z ]
-6 0
-4 0
-2 0
0N
orm
aliz
ed a
mpl
itud
e [d
B]
1 0 0 k 1 M 1 0 M 1 0 0 M
C M R R = c o m m o n s ig n a l / d if fe re n tia l s ig n a l
d if fe ren tia l m o d e s ig n a l
c o m m o n m o d e s ig n a l
C M R R = -5 5 d B @ 1 0 0 M H z
FP 420 BPM Workshop 47M. Gasior, CERN-AB-BI
F req u en cy [H z ]
-1 0
-5
0
Nor
mal
ized
am
plit
ude
[dB
]
1 k 1 0 k 1 0 0 k 1 M 1 0 M 1 0 0 M1 0 0
s ig n a l
s ig n a l
IPU and AHC – Frequency Characteristics
A wire method with a 50 coaxial setup which the IPU is a part
signal – flat to 0.5 dB within 5 decades, almost 6 decades of 3 dB bandwidth (no compensation)
signal – 5 decades (four decades + one with an extra gain for low frequencies)
BW: 1 kHz – 150 MHz (> 5 decades)
BW: 300 Hz – 250 MHz ( 6 decades)
FP 420 BPM Workshop 48M. Gasior, CERN-AB-BI
IPU and AHC – Displacement Characteristics
[mm] 05.078.9position vertical
[mm] 01.061.9positionhorizontal
V
H
-1 0 -8 -6 -4 -2 0 2 4 6 8 1 0W ire d isp lacem en t [m m ]
-1
-0 .8
-0 .6
-0 .4
-0 .2
0
0 .2
0 .4
0 .6
0 .8
1
Rat
io
/
D isp lacem en t m ax . = 2 0 m m
-6 -4 -2 0 2 4 6H o rizo n ta l (H ), v e rtic a l (V ) d isp lac em en t [m m ]
-0 .2
-0 .1
0
0 .1
0 .2L
inea
rity
err
or [
mm
]H e rro r = V e rro r =
D isp la c em en t m a x . = 2 0 m m
s ig n a l is c o n s ta n tw ith in re so lu tio n o f th e m e a su re m e n t o f 0 .1 %
F req u e n c y = 1 M H z
9 .6 1 / + 0 .0 1 [m m ]9 .7 8 / + 0 .0 5 [m m ]
x = H
x =V
x - w ire d isp lac e m e n t [m m ]H
x - w ire d isp lac e m e n t [m m ]V
H
V
A thin wire forming a coaxial line was displaced diagonally across the pick-up aperture. The measurement was done with a network analyzer: signal was applied to the wire and hybrid signals were observed.