FORMING RESERVED OUTPUT SIGNAL OF AN ATOMIC CLOCK ENSEMLE
K. Mishagin, I. Chernyshev, V. Soloviov, S. Podogova
6th International Symposium “METROLOGY OF TIME AND SPACE”
«Vremya-CH», Nizhny Novgorod, Russia
MotivationModern atomic clock ensemble etalons are required to produce continuous output signal� long continuous measurements� critical applications: communication with space
stations, etc.
Requirements to reserving system:
� Failure of certain atomic clock must not lead to phase/frequency jumps of the output signal
� Designed system is desired to be full-automatic� It is attractive to get physical signal possessing
frequency stability of ensemble weighted average
1 PPSCLOCK-1
CLOCK-2
CLOCK-n
Sw
itch
Computer
Phase comparator
orTime interval
counter
5 MHz 1 PPS
5 MHzAOG-1
AOG-2
AOG-n
1 PPS
5 MHz
1 PPS
5 MHz
Standard approach to output signal reserving
Standard approach to output signal reserving
Disadvantages:
• Long time for input signal analysis and commutation • Unavoidable phase/frequency shift during commutation• System complexity
Alternative approach∆f1,i
∆f2,i
∆f3,i
CLOCK-1
CLOCK-2
CLOCK-n
CLOCK-3M
ulti-
cha
nne
l pha
se (
fre
que
ncy)
com
para
tor
Pro
cess
or Voltage controlled quartz
oscillator5 MHz
DAC
Former of output signals
f1
fn
5, 10, 100 MHz, 1 Hz
1 PPS synch.
f2
f3
Scheme for output signal reserving in atomic clock ensemble
Real-time atomic clock
combinerVCH-317
Advantages:
� Fast detection and program detaching of failure signal� No phase/frequency shifts due to attaching/detaching
input signals� Can be realized in one device and reserved additionally � Frequency stability of output signal can be improved (it
can be better than the stability of the best reference standard)
PID-control algorithm for frequency stabilization
( ) ( )( )
∆
−=
+−−−−−∆+=
−
−−−+
1
2111
1
2DACDAC
nnn
nnnd
nnp
ni
nn
xxy
yyykyykyk
τ– relative frequency difference
– programmed frequency offset Loop sample time τ = 10 ms
Output frequency calculation
∑=
++=N
nn
Nn fwtf
1out νδ
ki, kp, kd are optimized Introduced phase noise and AVAR are minimized
Frequency instability introduced by the system
100
101
102
103
10-17
10-16
10-15
10-14
10-13
τ, s
σ y(τ
)HROG-5
AOG-110
VCH-317
Time TechClean-up osc.
No temperature stab.
in the room
Optimal weights selection problem
min2317
1
222out →+=∑
=σσσ
N
iiiw
∑=
−
−=
N
kk
iiw
1
2
2
)(
)()(
τσ
τστ
Output signal frequency instability is minimized for single averaging time only!Possible solutions:
1) Virtual atomic time scale + control of auxiliary oscillator 2) Multi-scale control
Frequency stability of the output signal
∑=
=N
nnn fwf
1out
∑=
−=∆N
n
Sn
Snk ywU
1
One-time-scale control algorithm:
Two-time-scale control algorithm:
( )∑ ∑= =
−−−=∆
N
n
N
m
Lm
Ln
Lm
Sn
Snk yywywU
1 1
Addition long averaging time estimation of frequency differences is required
( )∑ ∑= =
−−−=∆
N
n
N
m
Lm
Ln
Lm
Sn
Snk yywywU
1 1
Weights estimation for two-scale frequency control:
∑=
−
−=
N
k
Sk
SnS
nw
1
2
2
)(
)(
τσ
τσShort time:
Long time: ∑=
−
−
= N
k
Lk
LnL
nw
1
2
2
)~(
)~(
τσ
τσ
Estimation of frequency stability of reference signals is needed
∑=
−
−=
N
k
Sk
SnS
nw
1
2
2
)(
)(
τσ
τσ
∑=
−
−
= N
k
Lk
LnL
nw
1
2
2
)~(
)~(
τσ
τσ
Results of modeling. Dynamics of weights
Summary
� Atomic clock combiner system seems to be effective for output signal reserving (fast detection and exclusion of invalid reference signals, no phase/frequency jumps)
� Simple modification of the algorithm allows to obtain output signal frequency stability better than the best input signal has for all τ
THANK YOU FOR YOUR ATTENTION!
WELCOME TO THE POSTER SECTION
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