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°
*Δ
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)
