Download - Time Calibration Tests
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Time Calibration Tests
Results using a waveform templateCross-talk measurementsStub asymmetry results
Kalle SulankeDavid HardtkeBob Stokstad
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DOR
DOM
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Scope at DOR
Scope at DOM
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One-way time = 1/2 round trip timeONLY IF
Symmetry in pulse generation and transmissionSignal processing same at both ends
Golden Rule of Time Calibration
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DORDOR
DOM
DOR - DOM test DOR - DOR test
DOR-DOR has same clock for transmitting and receiving
DOR-DOM AsymmetryTest
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DOR - DOR
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Series1Series2
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DOR-DOR baseline subtracted
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V
t
t=V/(V/t)
••
••
•
Clock period 50 ns
Time resolution < 5 ns
Rise time ~400 ns
-> linear algorithm should be OK
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-200.0
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Series1Series2
DOR-DOR shifted by one clock tick = 50 ns
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391 392-2.3 -2.3-1.3 0.70.7 1.70.7 2.73.7 4.74.7 8.77.7 21.7
21.7 43.7 -22.0 -57.945.7 73.7 -28.0 -51.975.7 109.7 -34.0 -54.0
108.7 148.7 -40.0 -54.8148.7 189.7 -41.0 -48.8 -50.6192.7 230.7 -38.0 -44.7233.7 270.7 -37.0 -46.3272.7 308.7 -36.0 -46.2311.7 338.7342.7 352.7354.7 346.7347.7 319.7318.7 277.7278.7 229.7
V t (ns)
t av
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Average asymmetry = -1.3 ns
RMS asymmetry = 1.1 ns
DOR - DOR test
DOR
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DOR Card
Av. Asymm RMS asymm
DOM A -1.3 ns 1.1 ns
DOM B -1.2 ns 1.1 ns
DOR Card Test
of Two DOM Configuration
DOM A = 20 cm stub
DOM B = 40 cm cable
DO
R
DO
M A
DO
M B
• •
Runs A_02_04N
B_02_04N
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Timing Waveform Analysis• To get roundtrip time, need to analyze waveform:
– Template method -- compare two waveforms and calculate time shift
– Fitting method -- Fit each waveform with function• Failed fit functions -- Error Function, Gaussians, Polynomials• Best fit functions:
€
y = t − t0a
y > 0 ADC(y) = ped + Ay −3 / 2e−b(y+1/ y )
y <= 0 ADC(y) = pedDOMA_13_188
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Waveform Analysis (cont.)Linear fit over limited range, calculate crossing point
with pedestal
Fit range
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Round-Trip times using three methods
Waveform comparisonrms = 0.9 ns
Linear fit rms = 3.9 ns
Complicated fitrms = 7.2 ns
Note: absolute scale on x-axis not adjusted properly. OK for residuals, however.
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Using measured waveform as template appears promising.
Simple, fast, accurate.
Robust? (likely)
Candidate for use in ice.
Waveform Analysis Summary
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NOX_01_A
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DOR - DOM waveforms
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DOR, DOM_B
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DORDOM_B
Better symmetry after some component adjustments
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DOR - DOM typical results:
Round trip time rms ~ 1 nsfor 3.4 km cable in lab
using template
Boards otherwise "quiet"
No transmission of data in other twisted pair.
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Cross-talk studies
•DOR - DOM•3.4 km Ericsson quad on spool•Measure round trip rms deviation with and without data xmission at (1 Mbit/s) in other twisted pair
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Cross-talk measurement results
round trip residual (rms ns)
DOM A DOM B
Data transmission off 1.1 0.9to Ericsson quad
Data transmission on 4.4 4.7in Ericsson quad
Runs X01_A,B NOX01_A,B
Does Cross-talk occur in quad or on DOR card?
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Cross-talk measurement results, cont.
round trip residual (rms ns)
DOM A DOM B
Data transmission on 1.5 1.5to another quad
Data transmission on 4.4 4.7in Ericsson quad
Runs X01_A,B X03_A,B
=> Most Cross-talk occurs in quad
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Cable Cross Talk rms =4.4 ns
-15.0
-10.0
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rms =1.5 ns no cable x-talk
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Cable cross-talk rms =4.4 nsNo cable cross-talk rms =1.5 ns
Round Trip Time Residuals
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Cross-talk, cont.• Look at pedestal region:
Communications OFF Communications ON
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Cross-talk
• Calculate rms of signal in baseline region:
Data transmission in another cable
=> Most cross talk is in cable
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Cross-talk, cont.Try to reduce cross talk by using trapezoidal
communications pulse
Result
rms DOM A rms DOM B
4.4 ns 6.0 ns=> No Help
Runs X05_A,B_trap
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Timing error budget for clock calibration is 5 ns total -including frequency, offset, asymmetry
DOM clock calibration random systematic quad sumfrequency (sqrt 2 * intrinsic) 2.82clock drift 1offset (1/2 up-down asymmetry, component variations) 4DOM clock calibration subtotal 2.99 4 5.00
Conclude need to shut down data transmission during RAPCAL in order to meet timing requirement, given cross-talk levels in Ericsson quad.
Synchronized shutdown of communications for calibration is now the planned operating mode.
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Cable Stub TestsNo Stub Configurations
DOR
DOMa DOMb
15 cm 15 cmterminatedunterminated
3.4 km
cable end
DOR
DOMbDOMa
15 cm 1750 cm3.4 km
1
2
DOR, DOMa, and DOMb are actually one DOR card
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Cable Stub TestsStub Configuration
DOR
DOMb
DOMa
130 cm
1750 cm3.4 km
3
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Stub test results (preliminary)
DOMa DOMbasym rms asym rms
15-15 49.9 0.7 49.7 0.515-1750 49.1 0.5 49.7 0.5130-1750 49.7 0.4 49.8 0.7(NB 1 clock tick = 50 ns. Above absolute asymmetry is due to systematic logic error and is < 1ns.)
DOR card has single clock for all 3 channels
=> Can measure up - down asymmetry
Use centroid of positive portion of pulse
These results suggest that 1.3 m cable stub does not introduce an asymmetry with measurable effect on time calibration.
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