EX-219 Datasheet, PDF (6/9 Pages) Vectron International, Inc – Hi-Reliability Evacuated Miniature Crystal Oscillator

EX-219
Hi-Reliability Evacuated Miniature Crystal Oscillator (EMXO)
Application Notes
All data and notes are for reference only
1. EMXO Technology
The EMXO is an Oven Controlled Crystal Oscillator (OCXO)
hermetically sealed in an evacuated package. It is comprised of
a heated substrate (oven) and an output substrate. The oven is
mounted on a thermally insulated structure that maintains a
nearly constant temperature at about +95°C over the operating
temperature range whereas the output substrate is mounted
directly on the case. Unlike a conventional OCXO, the EMXO is
sealed in an evacuated package using high internal vacuum as
the insulation medium to achieve lower power consumption and
faster warm-up time.
2. Crystal Resonator
A doubly rotated crystal (IT-Cut), which is stress compensated,
is used to obtain good phase noise, better aging rate and lower
g-sensitivity. The crystal has a 4-point mounting structure for
robustness and low g-sensitivity. Synthetic swept quartz is used
for the flight model (FM) to achieve higher radiation tolerance.
The Temperature Characteristic (TC) of an IT cut crystal in a 3^rd
order polynomial function has an inflection temperature at
+75°C and an upper turn temperature (UTP) of +95°C. To
obtain the advantage of minimal frequency sensitivity, the oven
temperature is set at or around the UTP of the crystal. Figure 1
shows typical Temperature Characteristic (TC) of an IT cut
Crystal.
operating temperature. The warm-up time is inversely
proportional to the case temperature. Since the EMXO is
evacuated and has much less thermal mass than a
conventional OCXO, its warm-up time is much faster. Figure 2
shows the typical Warm-up Power characteristic at -40°C and
+25°C.
Warm -up Characteristics
2.5
2.0
1.5
1.0
0.5
0.0
1
-40^oC
+25^oC
10
100
1000
Time (second)
10000
Figure 2
During warm-up, the output frequency follows the TC of the
crystal frequency until the oven power has cut back to the
steady state condition. After oven cut back, the frequency still
slowly changes until the oven temperature reaches equilibrium
state. Figure 3 shows the Warm-up Frequency characteristic at
-40°C and +25°C.
20
0
-20
-40
-60
-80
-100
-120
-50 -25
IT Cut Crystal
0
25
50
Temp (c)
75
100 125
Warm -up Characteristics
10
8
+25^oC
6
4
2
0
-2
-4
-6
-40^oC
-8
-10
1
10
100
Time (second)
1000
Figure 3
10000
Figure 1
4. Operating Temperature Characteristic
3. Warm-up Characteristic
At cold turn-on, the oven is fully powered and the oven
temperature rises to the preset temperature which is about
95°C. When the set temperature has been reached, the oven
power consumption is cut back to the steady state condition. At
steady state, the oven is proportionally controlled and maintains
a nearly constant oven temperature. The turn-on power
consumption must be higher than the steady state power to
prevent power starving, especially at the cold end of the
The operating temperature specified herein is the device case
temperature. Since the oven is proportionally controlled, its
power consumption is inversely proportional to the case
temperature. Figure 4 shows the steady state power versus
case temperature. If the case temperature rises above the
maximum operating temperature, the oven will shut off. Thus,
the output frequency is no longer stable and follows the TC for
the crystal. Figure 5 shows frequency versus case
temperature. Although the maximum operating temperature is
+85°C, the case temperature can increase up to +95°C without
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