Time Calibration Tests

Time Calibration Tests

Results using a waveform templateCross-talk measurementsStub asymmetry results

Kalle SulankeDavid HardtkeBob Stokstad

DOR

DOM

Scope at DOR

Scope at DOM

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

DORDOR

DOM

DOR - DOM test DOR - DOR test

DOR-DOR has same clock for transmitting and receiving

DOR-DOM AsymmetryTest

DOR - DOR

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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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DOR-DOR shifted by one clock tick = 50 ns

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

Average asymmetry = -1.3 ns

RMS asymmetry = 1.1 ns

DOR - DOR test

DOR

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

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

Waveform Analysis (cont.)Linear fit over limited range, calculate crossing point

with pedestal

Fit range

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.

Using measured waveform as template appears promising.

Simple, fast, accurate.

Robust? (likely)

Candidate for use in ice.

Waveform Analysis Summary

NOX_01_A

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DOR - DOM waveforms

DOR, DOM_B

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DORDOM_B

Better symmetry after some component adjustments

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.

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

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?

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

Cable Cross Talk rms =4.4 ns

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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

Cross-talk, cont.• Look at pedestal region:

Communications OFF Communications ON

Cross-talk

• Calculate rms of signal in baseline region:

Data transmission in another cable

=> Most cross talk is in cable

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

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.

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

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DOR, DOMa, and DOMb are actually one DOR card

Cable Stub TestsStub Configuration

DOR

DOMb

DOMa

130 cm

1750 cm3.4 km

3

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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