Signal Delay Measurement Method for Timing ...

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Beam Instrumentation Workshop 2010. GSI. Rx transmission fibre circulator. Tx phase - .... Helmholtz Centre for Heavy Ion Research GmbH. RF Department.
Signal Delay Measurement Method for Timing Systems – Part 1

GSI

M. Bousonville, GSI, Darmstadt, Germany J. Rausch, Technische Universität Darmstadt, Germany

Helmholtz Centre for Heavy Ion Research GmbH RF Department Darmstadt, Germany

Beam Instrumentation Workshop 2010 Abstract

Measurement Method

→ Accuracy 100 fs → Cost efficient → Measurement of absolute delay

Measurement signal: a sequence of sinusoidal oscillations Step 1: Low frequency ⇒ absolute delay measurement unit

location:

Introduction A conventional timing system

Tx

Rx

propagation:

phase difference:

Rx

control

reference signal

τ M ,1 =

FAIR timing system with dense wavelength division multiplex Advantages: 1. Low attenuation ≈ 4 dB 2. Reference signal ≠ measurement signal

τ



∆ϕ M ,1 360 °

High accuracy

Indexes: τ M ,step τ ∆ϕ M , step f M ,step

∆ϕ M ,1 2 ⋅ 360°

⋅ TM ,1

measurement signal

⋅ TM ,1

(1)

f M ,1

Delay measured Delay true value Measured phase difference Measurement frequency

TM , step K step

τ accu, step ∆ϕ accu,step

= TM ,1 > 2τ

clock 2

Tx

λ2

multi- λ1, λ2 plexer

λ1, λ2, λM

Add/Drop

SMF

λ1

λM FBG

λ1, λ2

demultiplexer λ2

Rx

clock 1

Rx

clock 2

circulator transmission unit

λM Tx

φsend

phase comparator

φreceive

λM Rx

∆ϕ M , 2

TM,2

2τ = 2{ TM , 2 + K2

∆ϕ M , 2 360°

360°

receiver unit

I2

⋅ TM , 2

⋅ TM , 2

φM,2 = (φsend – φreceive) mod 360°= 220°



Integer factor K2

Second delay value (step = 2):

τ M , step =

K step 2

⋅ TM , step +

Accuracy in each step:

∆ϕ M , step 2 ⋅ 360°

⎢ 2τ M , step −1 ⎥ K step = ⎢ ⎥ (5) ⎢⎣ TM , step ⎥⎦

⋅ TM , step (4)

τ accu , step =

∆ϕ accu , step 2 ⋅ 360°



1 f M , step

Step 3 to N

d) From Eq. (3) follows measurement unit

ΔφM,2*

a) Increasing measurement frequency each step. b) Calculate delays for each step according to Eq. (4). c) Approximately ∆ϕ accu, step is not depending on f M , step

fM I1

360°

TM,2

(2)

Measurement signal period Integer factor Accuracy delay determination Accuracy of phase comparator

→ Basic condition for the following measuring method λ1

time:

Boundary condition:

1

360°

phase difference:

ΔφM,1 = φsend – φreceive = 160°

First delay value:

DWDM

Tx

φreceive = -940°

backward

τ

time:

2τ =

phase -comparator

clock 1

φsend = 0°

phase:

φreceive = -160°

forward

reflector splitter

phase shifter

Rx

measurement unit

measurement signal

transmission fibre

splitter

FBG reflection point

⇒ Low accuracy

circulator reference signal generator

measurement unit

location:

measurement unit

φsend = 0°

phase:

Disadvantages: 1. High attenuation ≈ 15 dB 2. Reference signal = measurement signal

FBG reflection point

Step 2: Higher frequency ⇒ better accuracy

f M , step ↑ ⇒

τ accu , step ↓

Accuracy getting better each step

(3)