Performance Evaluation
59
CG635 Synthesized Clock Generator
Calculate the rms noise, N
T
, using the equation N
T
= (N
0
2
+ 4N
1
2
)
1/2
Calculate the rms
jitter, N
J
, from the rms noise using the equation N
J
= N
T
/2
ʌ
F, where F is the carrier
frequency.
For example, if N
0
= 2.3 mradrms and N
1
= 0.66 mradrms and F = 620.80 MHz, then
N
T
= (2.3
2
+ 4×0.66
2
)
1/2
= 2.65 mradrms
and
N
J
= 2.65×10
-3
/(2×3.14×620.80×10
6
) = 0.68 ps.
The calculated jitter should be less than the maximum allowed jitter specified in Table
32.
Timebase Calibration
The accuracy of the internal timebase may be tested against a house reference if it is
known that the house reference has a superior stability and accuracy than the timebase
installed in the CG635. Use the setup shown in Figure 11 to test the accuracy of the
timebase.
Figure 11: Setup for timebase calibration
The accuracy and stability of the CG635 timebase depends on the type of timebase
installed. An optional timebase, if installed, can be identified on the rear panel of CG635
under the serial number as Option 2, OCXO timebase, or Option 3, Rubidium timebase.
If the standard timebase or OCXO is installed, an FS725 Rb frequency standard may be
used as the 10 MHz reference. If a rubidium timebase is installed, a cesium based
reference will be required as a reference.
SR620 Configuration
Use the following procedure to set up the SR620:
1.
With the power off hold down the ‘CLR’ button in the DISPLAY section and
turn the power on. This resets the SR620 to default settings.
Q
Q
CMOS
CG635
10 MHz
Reference
SR620
EXT A
B REF
10 MHz IN
10 MHz OUT
