Precision
Oscillator
Overview
Hugo Fruehauf
April 2007
hxf@fei-zyfer.com
Frequency Electronics Inc.
Discussion Outline
• Quartz Crystal Oscillators
• Atomic Oscillators
• Atomic Oscillator Size History & Future
• Performance Characteristics
Frequency Electronics Inc.
2
Main Categories of Precision Quartz Oscillators
+25°c
Temperature
Sensor
Compensation
Network
∆f
f
+1 x 10-7
-45°c
+100°c
XO
-1 x 10-7
Temperature Compensated (TCXO)
∆f
Oven
f
XO
Oven
Control
-45°c
-1 x 10-9
Oven Controlled (OCXO)
∆f
f
Ovens
Oven
Controls
+100°c
Temperature
Sensor
XO
Temperature
Sensors
Double Oven Controlled (DOCXO)
Frequency Electronics Inc.
+1 x 10-9
+1 x 10-10
-45°c
+100°c
-1 x 10-10
Quartz Crystal Oscillators have no wear out
mechanism. If manufactured properly, should
last 25 years or more
3
Precision Crystal Oscillators from raw materials
Z
Resonator
• Dynamic Cleaning
• Crystal Cutting i.e.
SC, AT, FC, etc
• Rounding
X
• Polishing
• Plating
Qz Disc
• Mounting
Crystal Oscillator
Y
• Tuning
• Sealing
• Testing
Piezoelectric
properties of quartz
Typically
0.75” x 1.5” x 1.5”
Frequency Electronics Inc.
4
Typical Resonator Package Examples
Frequency Electronics Inc.
5
The Piezoelectric Effect
Y
Y
_
+
+
+
_
_
_
_
+
+
+
+
_
_ -
_
+
• • +
+
+
+
+
+
+
_
+
Un-deformed lattice
+
_
_
X
_
_
_
+
_
+
+
_
_
_
_
+
+
_
_
X
+
+
+
_
_
_
+
_
_
_
+
_
_
+
+
+
+
+
+
_
_
_
_
+
+
+
+
+
_
_
_
_
_
+
+
+
+
_
_
_
_
_
+
Strained lattice
The piezoelectric effect provides a coupling between the mechanical
properties of a piezoelectric crystal and an electrical circuit.
Frequency Electronics Inc.
Courtesy, John Vig (Ft. Monmouth NJ)
6
Modes of Piezoelectric Motion
Flexure Mode
Extensional Mode Face Shear Mode
Thickness Shear Fundamental Mode Third Overtone
Thickness Shear Thickness Shear
Mode
Courtesy, John Vig (Ft. Monmouth NJ)
Frequency Electronics Inc.
7
Zero Temperature Coefficient Quartz Cuts
90o
60o
30o
IT
SC
z
θ
0
-30o
θ
gl y d
n
i
S tate
Ro t
Cu
FC
AT
SBTC
BT
-60o
Do
ub
Ro l y
ta t
Cu e d
t
-90o
θ
y
φ
x
xl
0o
10o
φ
20o
30o
The AT, FC, IT, SC, BT, and SBTCcuts are some of the cuts on the
locus of zero temp. coefficient cuts.
Courtesy, John Vig (Ft. Monmouth NJ)
Frequency Electronics Inc.
8
Oven Effect on Temperature Coefficient
Frequency
TURNOVER
POINT
OVEN SET POINT
TURNOVER
POINT
OVEN
OFFSET
2∆ To
OVEN CYCLING RANGE
Typical f vs. T characteristic
for AT and SC-cut resonators
Temperature
Courtesy, John Vig (Ft. Monmouth NJ)
Frequency Electronics Inc.
9
Aging Mechanisms
z Mass transfer due to contamination
Since f ∝ 1/t, ∆f/f = -∆t/t; e.g., f5MHz ≈ 106 molecular layers,
therefore, 1 quartz-equivalent monolayer ⇒ ∆f/f ≈ 1 ppm
z Stress relief in the resonator's: mounting and bonding structure,
electrodes, and in the quartz (?)
z Other effects
{
{
{
{
{
{
{
Quartz outgassing
Diffusion effects
Chemical reaction effects
Pressure changes in resonator enclosure (leaks and outgassing)
Oscillator circuit aging (load reactance and drive level changes)
Electric field changes (doubly rotated crystals only)
Oven-control circuitry aging
Frequency Electronics Inc.
10
Summary - Most Significant Effects
Temperature
Control temperature deltas with ovens
Frequency Aging
Control aging with superior manufacturing technology
Dynamic Environments (vibration, shock, acceleration)
Control sensitivity with:
- Superior manufacturing technology
- Shock mounts
- Electronic g-compensation technology
Frequency Electronics Inc.
11
Typical Loiter Aircraft and Helicopter Random Vibration
0.5
V i b r a t i o n g 2/ H z
5g2/Hz
0.4
0.3
Helicopter
0.2
Loiter Aircraft
0.1
0.08g2/Hz
0.04g2/Hz
0
10
20
30
Frequency Electronics Inc.
40 50
70
100
Frequency (Hz)
200
300
1000
12
g-Compensation Technology
Sensing devices mounted in
each axis
Vibration applied
to the Oscillator
[2]
Quartz
Disk
Z
Г = (x2 + y2 + z2)½
[1]
X
Y
The actual
product
encloses the
disk with a cap
Quartz Crystal
Resonator base
Frequency Electronics Inc.
Sensing
devices
respond
[3]
[5]
Quartz
Resonator
responds
[4]
[7]
[6]
Electronic Compensation
Oscillator
Output
13
g-Compensation & Shock Mount Approach
–Acceleration sensitivities better than
2E-12/g
–Improvements of greater than 30dB
–Optimized compensation from DC to
200 Hz
–Broadband compensation from DC to
2 KHz is possible
–Economies in manufacturability
–Small package < 5in3
Compensated
Uncompensated
Uncompensated
Compensated
Frequency Electronics Inc.
14
Discussion Outline
• Quartz Crystal Oscillators
• Atomic Oscillators
• Atomic Oscillator Size History & Future
• Performance Characteristics
Frequency Electronics Inc.
15
Stand-alone Precision Oscillator
Technologies
Rubidium Vapor Atomic Oscillator
Qz
Osc.
Rb Vapor
Phy Pkg
Quartz
Crystal
Oscillator
Cesium Beam Atomic Standard
Qz
Osc.
Principle
Oscillator in
use today
Out
• Qz oscillator
frequency-locked to
Hyperfine Rb
frequency of ~6.8 GHz
Qz
Osc.
Cs Beam
Phy Pkg
Out
Hydrogen Maser Atomic Oscillator
Hm
Fountain
Phy Pkg
Precision
Quartz Crystal
Oscillators
Frequency Electronics Inc.
Qz
Osc.
Atomic
Oscillators
Out
• Qz oscillator
frequency-locked to
Hyperfine Cs
frequency of ~9.2 GHz
• Qz oscillator
frequency-locked to
Hyperfine Hm
frequency of ~1.4 GHz
(Passive Hm) or
Phase-locked to ~1.4
GHz (Active Hm)
16
Atomic Energy Levels
Electron Energy Levels -
Electrostatic interaction between Proton and Electron (+ and - charges)
(Energy out or in is generally in the
infrared-visible-UV frequencies)
Collapsing
the orbit
releases
energy
Fine Structure
Expanding orbit
requires energy
- Interaction between electron spin dipole moment and the magnetic field due to
the electron’s orbital motion. ~1/50 of the first energy level.
(Energy out or in is generally in the
microwave frequency area)
Hyperfine Structure
- Magnetic dipole interaction between the electron spin dipole moment
with the nucleus. ~1/1000 of fine structure interaction.
N
S
S
N
Zeeman Effect -
(Energy out or in is generally in the
microwave frequencies and below)
f ≈ 1.4 GHz for Hydrogen
f ≈ 6.8 GHz for Rubidium
f ≈ 9.2 GHz for Cesium
Magnetic interaction between external magnetic field and electron and
proton spin dipoles.
(Energy out or in is generally in the
audio frequency area and above)
Frequency Electronics Inc.
(Courtesy: Ed Mattison, Smithsonian from his tutorial 12-92 (a H. Fruehauf modification of his chart)
17
Frequency Electronics Inc.
18
Atomic Vapor Oscillator
(5)
Glass Cells (3)
Heaters (2)
Photo Cell (7)
DC+Mod Freq
87Rb
Lamp (4)
85Rb
(could also be a
Laser Diode)
~6.8 GHz
Servo
(8)
Qz Osc
(9)
Output
Rubidium (1)
Synth
(8a)
(6)
10 MHz
Atomic Vapor Oscillators have
no wear out mechanism. If
manufactured properly, should
last 25 years or more
Frequency Electronics Inc.
(could also be a
Cesium Source)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Active Element of Choice
Controlled Environment
Element Container
Atomic Pump
Resonator
Irradiation Source
State Detector(s)
Control Electronics
Frequency Source
19
Optical Pumping Process
fc>fRb
fm
t
t
fc=f 2f
m
Rb
f
fm
fm
fm
t
t
t
fc<fRb fc=fRb fc>fRb
t
Modulated
Photo Current
Output
fm
Cavity (6.834, 682, 613 GHz)
Frequency
Modulation
Photo Current
fc<fRb
Dip Due to Rb
Resonance
fc
Microwave Frequency
Resonance Cell
87Rb
85Rb
Filter
Cell
Photo
Detector
6.8 GHz
from Osc.
C
S
(20 to 50 ns)
N
N
S
Frequency Electronics Inc.
87Rb
Lamp
Spectral
Line
Filtered
Spectral
Line
Excited
B
A
6.8 GHz
Separation
(~0.15 ns)
20
Modulation Scheme
Dip Due to Rb Resonance
fc<fRb
fm
fm
~500 Hz
t
Photo Current
t
fc=fRb
2fm
fm
t
t
t
fc=fRb
fc>fRb
f
fc<fRb
Frequency Electronics Inc.
Frequency
Modulation
t
Modulated Photo
Current Output
fc>fRb
Microwave Frequency
fc
21
Rubidium Vapor Atomic Oscillator
Size: ~1.5” x ~3” x ~3”
Physics Package
Frequency Electronics Inc.
22
Cesium Beam Atomic Frequency Standard
State Selection
Magnets (7)
Hot Wire Ionizer (7)
DC+Mod Freq
(2)
Servo
(8)
Cesium Oven (4)
Cesium Source (1)
(10)
Beam Tube (3)
(6)
(5)
~9.2 GHz
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Active Element of Choice
Controlled Environment
Element Container
Atomic Pump
Resonator
Irradiation Source
State Detector(s)
Control Electronics
Frequency Source
Ion Pump and Getters
Frequency Electronics Inc.
Synth
(8a)
5 MHz
Cesium Oscillators have a wear
out mechanism, mainly due to the
detector getting noisy from ungettered ions. It begins to show up
in 7 to 10 years
Qz Osc
(9)
Output
23
Passive Hydrogen Maser Atomic Oscillator
(2)
(5)
Bulb (3)
Receiving Antenna (7)
~1.4 GHz
~1.4 GHz
(10)
Synth
(8a)
State
Selection
Magnets (7)
(6)
Servo
(8)
H
(2)
H2 Disassociator (4)
Hydrogen Source (1)
Qz Osc
(9)
Output
H2
Passive H-Maser Oscillators have
a wear out mechanism, mainly
from Hydrogen depletion and Ion
Pump failures, which begin to
show up in 5 to 7 years
Frequency Electronics Inc.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Active Element of Choice
Controlled Environment
Element Container
Atomic Pump
Resonator
Irradiation Source
State Detector(s)
Control Electronics
Frequency Source
Ion Pump and Getters
24
Active Hydrogen Maser Atomic Oscillator
(5) & (9)
(2)
Bulb (3)
Receiving Antenna (7)
~1.4 GHz
(10)
RCVR &
PLL (8a)
State
Selection
Magnets (7)
(6)
H
(2)
H2 Disassociator (4)
Hydrogen Source (1)
Qz Osc
(8)
Output
H2
Active H-Maser Oscillators have a
wear out mechanism, mainly from
Hydrogen depletion and Ion Pump
failures, which begin to show up in
3 to 5 years
Frequency Electronics Inc.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
Active Element of Choice
Controlled Environment
Element Container
Atomic Pump
Resonator
Irradiation Source
State Detector(s)
Control Electronics
Frequency Source
Ion Pumps and Getters
(6) No Irradiation Source;
the Cavity Oscillates and thus
is the Frequency Source, not
the Qz Oscillator as in
previous configurations
25
Discussion Outline
• Quartz Crystal Oscillators
• Atomic Oscillators
• Atomic Oscillator Size History & Future
• Performance Characteristics
Frequency Electronics Inc.
26
Volume History of Rubidium and Cesium Osc.
Volume (size) in Cubic Inches
105
Vapor Std's
Vapor Std Best Guess
Beam Std
Beam Std. Best Guess
104
~5500 in3 (Lab)
3
~2400 in3 (HP, TRACOR, GENRAD)
103
3
(1 in = 16.4 cm )
3
~350 in (FTS)
3
~ 180 in
3
102
~64 in (Efratom)
Cesium Beam
3
60 in
3
47 in (Efratom)
3
24 in (Efratom, EG&G)
3
~13 in (FEI, TNT)
101
~7.35 in3 (Symmetricom)
Rb Vapor
6.0
~6.4 in3 (AccuBeat)
3.0
100
~1 in3 ?
1.8
0.6
0.3
10-1
0.18
1960
1970
Frequency Electronics Inc.
83 85
1980
93
1990
99
02
2000
06
12
(DARPA Man-Pac
Spec, Low Pwr)
~1.0 cm3
(my guess, HF)
16
2010
27
Discussion Outline
• Quartz Crystal Oscillators
• Atomic Oscillators
• Atomic Oscillator Size History & Future
• Performance Characteristics
Frequency Electronics Inc.
28
Accuracy, Precision, and Stability
f
Accurate but
not precise
Not accurate and
not precise
Precise but
not accurate
f
f
Accurate and
precise
f
0
Time
Stable but
not accurate
Time
Not stable and
not accurate
Frequency Electronics Inc.
Time
Accurate but
not stable
Time
Stable and
accurate
29
Qz Osc Best-in-Class Frequency Domain Noise
(Phase Noise for a 10 MHz Carrier)
60
70
80
90
100
CMAC CFPO-LN
dBc/Hz
110
FEI-Zyfer 10 MHz- LN
Module (- 4036)
120
130
FEI State of Art
140
150
HP 10811 Qz
160
170
180
10-1
1Hz
Frequency Electronics Inc.
10 Hz
100 Hz
Frequency (Hz)
1KHz
10KHz
100KHz
30
FEI 6.3 MHz LN Osc. Test Plot, 03-09-2006
FEI State of Art
Equivalent for 10 MHz
Measurement problem;
should be at -165 floor
HP 10811 Qz
Frequency
FrequencyElectronics
ElectronicsInc.
Inc.
31
31
Qz Osc Best-in-Class Time Domain Noise
(Short-term Stability for 10 MHz)
10-8
Allan Variance½, σy(τ)
10-9
10-10
FEI-Zyfer 10 MHz- LN
Module (- 4036)
10-11
HP 10811 Qz
10-12
FEI State of Art
10-13
1 Day
1 Hr
10 Hrs.
10-14
10-3
10-2
10-1
Frequency Electronics Inc.
100
101
102
Averaging Time, T(Sec.)
103
104
105
32
Comparison of Qz, Rb, GPS, Cs, and Maser
Time Domain Noise
10-10
Sym 5061A, Cs
Sym 5071A, Cs
GPS-Disciplined Qz/Rb
High Performance Rb
10-12
VR
1
(AllanVariance) 2, σy (τ )
10-11
Good Qz Osc
EM
Y
10-13
10-14
Kva
rz P
A(
ass
FE
I) V
ive
CH
Ma
ser
-10
06
Pa
Kva
s si
ve
rz A
Ma
ctiv
ser
eM
ase
r
Sym 5071A
Option 001 Cs
10-15
1 Hr
1 Day
10 Hrs.
1 Week
1 Mo.
10-16
1
10
Frequency Electronics Inc.
102
103
104
Averaging Time, T(Sec.)
105
106
33
Stability & Accuracy of Precision Oscillators
Short & Long Term
Stability
10-4
Accuracy
10-4
TCXO
10-5
Approx. Time Error at One Day
(Lab Conditions)
10-6
10-5
~250 ms
10-6
TCXO
~10 ms
10-7
10-7
MCXO
10-8
(Allan Variance) ½ [σγ(τ)]
Range
~300 µs
MCXO
10-9
10-11
~30 µs
~10 µs
GPS/Rb (Cs
Substitute)
STD. Cs
Space Qz & Su
per OCXO
10-12
~90 µs
OCXO
Low Cost
Rb
STD. Cs
10-10
OCXO
Hi-Perf. Rb
Hi-Perf. Cs
&
10-13
Space Rb
Passive - Hm
10-14
Active - Hm
10-15
~1 µs
~86 ns
~25 ns
~3 ns
~1 ns
10-8
O
r OC X
Supe
e Qz
Spac
t Rb
Cos
w
o
L
10-9
b
eR
pac
S
t
Cos
w
+ Lo
Rb
Rb
.
f
ace
r
p
e
S
P
Hierf.
Hi-P
GPS/Rb (Cs Subst)
& STD. Cs
s
C
.
rf
e
P
HiM
Passive - H
- HM
Active
10-10
10-11
10-12
10-13
10-14
~100 ps
10-15
10-16
1
10
100
1000
104
105
106
1-Day
Averaging Time in Seconds
Frequency Electronics Inc.
107
108
1-Year
Elapsed Time
34
500 MHz Osc Output; Best-in-Class
Frequency Domain Noise
(Qz and SAW combo)
Frequency Electronics Inc.
35
35
Typical Specs for Precision Quartz Oscillators
Basic Parameters
TCXO
OCXO (0.5” High) OCXO (0.75” High)
DOCXO
(Temp. Comp. XO) (Oven Control XO) (Oven Control XO) (Double Oven XO)
10 MHz, Sine
0.5 Vrms, 50 Ω
1 E-9
5 E-10
5 E-10
1E-11
1E-11
1E-10
5E-12
1E-11
1E-11
- 55 dBc/Hz
-115 dBc/Hz
-130 dBc/Hz
- 80 dBc/Hz
-135 dBc/Hz
-145 dBc/Hz
- 90 dBc/Hz
-135 dBc/Hz
-145 dBc/Hz
- 90 dBc/Hz
-135 dBc/Hz
-145 dBc/Hz
-75 dBc/Hz
-125 dBc/Hz
-145 dBc/Hz
--5E-7/yr
5E-10/day
2E-7/yr
2E-10/day
2E-8/yr
2E-10/day
2E-8/yr
5E-11/day
5E-10/yr
Temp Range
Frequency Stability
0° to 75°C
5E-7
0° to 75°C
2E-8*
0° to 70°C
2E-10
0° to 60°C
3E-10
Power Consumption
Warm-up Time
50 miliwatts
50 milisec
2 watts
10 min, 1E-8
3.5 watts
10 min, 1E-8
8 watts
4 min, ~1E-9
--12 Vdc± 10%
1E-9 for +/-10%
--12 Vdc± 10%
1E-9 for +/-10%
2E-11/Gauss
15 to 28 Vdc
2E-11 for +/-10%
2.0” x 2.0” x 0.75” H
3
3 in
< 0.22 lbs
2.0” x 2.0” x 1.0” H
3
4 in
< 0.3 lbs
3.0” x 3.0” x 1.4” H
3
13 in
0.75 lbs
Short Term Stab.
Phase Noise,
1s
10s
100s
1Hz
100Hz
1000Hz
Aging/Day/Month/Year
Magnetic Field Sensitivity
Input Volts Range
Supply Volts Sensitivity
--5 Vdc± 0.25%
1E-8 for +/-10%
Size
Volume
Weight
1.0” x 0.7” x 0.22” H
3
0.154 in
< 0.1 lbs
Frequency Electronics Inc.
--12 Vdc± 10%
1E-9 for +/-10%
1.5” x 1.5” x 0.5” H
3
1.125 in
< 0.15 lbs
0° to 75°C
2E-9*
2.5 watts
10 min, 1E-8
* With GPS learning algorithm, X20 improvement
10 MHz, Sine
0.5 Vrms, 50 Ω
Rubidium Osc.
10 MHz, Sine
0.5Vrms, 50 Ω
Output
10 MHz, Sine
0.5 Vrms, 50 Ω
For Reference Only
5E-12
1E-11
1E-11
10 MHz, Sine
0.5 Vrms, 50 Ω
3E-11
7E-12
3E-12
36