measurement of time difference - nict · measurement of time difference • using time interval...
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Measurement of Time Difference
Kuniyasu Imamura, Hiroyuki Itoh, Noboru Kotake and Fumimaru Nakagawa
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Outline
• Time Interval Counter• DMTD method
◆ Principle of DMTD◆ Measurement of Time Difference using DMTD system◆ Demonstration of DMTD system and comparison with
a commercial time interval counter.
• Clock transportation◆ Method of Clock transportation◆ Practice of Clock transportation
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Procedure of Measurement ofTime difference by SR620
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Procedure of Measurement ofTime difference by SR620
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Dual Mixer Time Difference (DMTD)
• Using two double balanced mixer, both a reference signal and a DUT signal are down-converted by the same local signal.
• Before and after the down-convert, a phase difference between Reference and DUT dose not change, but frequency is decreased.
• As a result, a time difference measured by TIC is amplified and a measurement precision of time difference is improved.
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Demonstration of DMTD
• Frequency stability of TIC(SR-620)• Frequency stability of DMTD system• Measurement of Cesium atomic clock by
TIC• Measurement of Cesium atomic clock by
DMTD system
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Measurement of Time Difference
• Using Time Interval Counter* Measurement of absolute value (using 1pps)*The precision is a few 10ps→ ~10s averaging time for Cs clock→ ~10000s averaging time for HM clock
• Using DMTD method*Measurement with high precision*Only measurement of relative value is possible.*Using carrier signal (ex. 5Mhz)*The precision is below a few 0.1ps→ We can measure the frequencies both Cs and HM from 1s averaging time.
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Frequency stabilities of measurement systems and atomic clocks
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Measurement of Time Difference and Cable Delay
using Clock Transportation
(1)Measurement of time difference between two clocks with some distance
(2)Measurement of cable delay
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●Check TIC parameter at each measurement ・Reference signal ・Trigger parameter(level,impedance,slope…)
Impedance □50Ω □HighSlope □positive □negativeTrigger level ______________V
Let’s practice Clock transportation !!(measurement of cable delay)
⑤Calculation
・Calculate the cable delay from ② and ④.
④ - ② Cable delay
_____ - _____ = ______
①Measurement-1
・Connect a reference cable to input-A of TIC.
・Set parameters of TIC
・Measure a time difference three times and
record a value and timeC2
0.000003277613
START STOP
Time Interval Counter
Portable Clock
CT measurement set
Process 1
(Tref(t1) -C0-τ1-C1)-(TPC(t1)-C2) …(1)
Reference Clock
Tref(t1) TPC(t1)
C1
Time : t1
τ1
τ2
C0
Time Time diff Jitter
_____ _____ _____
_____ _____ _____
_____ _____ _____
_____ _____ _____
1st
2nd
3rd
Avg.
①
②Measurement-2
・Connect a DUT cable to input-A of TIC.
・Set parameters of TIC
・Measure a time difference three times and
record a value and timeC2
0.000003277613
START STOP
Time Interval Counter
Portable Clock
CT measurement set
Process 2
Reference Clock
Tref(t2) TPC(t2)
C1
Time : t2
τ1
τ2
C0
(Tref(t2) -C0-τ2-C1)-(TPC(t2)-C2) …(2)
Time Time diff Jitter
_____ _____ _____
_____ _____ _____
_____ _____ _____
_____ _____ _____
1st
2nd
3rd
Avg.
②
③Measurement-3
・Connect a reference cable to input-A of TIC.
・Set parameters of TIC
・Measure a time difference three times and
record a value and timeC2
0.000003277613
START STOP
Time Interval Counter
Portable Clock
CT measurement set
Process 3
Reference Clock
Tref(t3) TPC(t3)
C1
Time : t3
τ1
τ2
C0
(Tref(t3) -C0-τ1-C1)-(TPC(t3)-C2) …(3)
Time Time diff Jitter
_____ _____ _____
_____ _____ _____
_____ _____ _____
_____ _____ _____
1st
2nd
3rd
Avg.
③
④Estimation
・Estimate the time difference between the reference
point and the portable clock at ② using linear fitting
Estimation from (1) and (3)
Process 4
Time
Time differencebetween Tref and Tpc
x
x
t1 t3t2
●(4)
(1)
(3)
(Tref(t2) -C0-τ1-C1)-(TPC(t2)-C2) …(4)
Time Time diff
_____ _____
_____ _____
_____ _____
①
③
④
④