Introduction 10
CG635 Synthesized Clock Generator
Clock Output
The CG635 interfaces to a number of optional clock receiver modules which can be used
to get a clock signal from the CG635 to where it is needed. The receiver modules
regenerate the clock locally providing the user with clean, fast clock edges, even if the
CG635 is several meters away. Receiver modules are available for generating most of the
standard CMOS and ECL signal levels.
All modules provide both +CLK and –CLK with a source impedance of 50
ȍ
, and
connect to the rear-panel RJ-45 connector using standard Category-6 cable. Table 5
summarizes the features of the optional receiver modules offered by SRS. The maximum
frequency (F
max
) listed in the table for each module is the maximum frequency at which
the module operates at specification. With the exception of the CG640, the modules
continue to operate above F
max
, but with reduced amplitude.
Table 5: Optional Receiver Modules
Model Description
Termination
Impedance
Transition
Time(max)
F
max
(2)
CG640 CMOS
(+5
V
cc
)
High Z
2.0 ns
105 MHz
(1)
CG641 CMOS
(+3.3
V
cc
) High Z
800 ps
250 MHz
CG642 CMOS
(+2.5
V
cc
) High Z
800 ps
250 MHz
CG643 PECL
(+5
V
cc
)
High Z
800 ps
250 MHz
CG644 PECL
(+3.3
V
cc
) 50
ȍ
100 ps
2.05 GHz
CG645 PECL
(+2.5
V
cc
) 50
ȍ
100 ps
2.05 GHz
CG646
RF (+7 dBm)
50
ȍ
100 ps
2.05 GHz
CG647 CML/NIM
50
ȍ
100 ps
2.05 GHz
CG648 ECL
50
ȍ
100 ps
2.05 GHz
CG649 LVDS
50
ȍ
100 ps
2.05 GHz
Notes
: (1) Output is set to logic ‘0’ above F
max
.
(2) Maximum operating frequency is limited by the CAT-6 cable length.
The maximum frequency may also be limited by the CAT-6 cable length. At 2 GHz, the
cable may be up to 10 feet long. At 10 MHz, the cable may be up to 200 feet long.
Figure 3 summarizes the limitation on maximum frequency due to cable length.
If clock regeneration is not needed, the user can interface directly to the clock signals
provided on the various pins of the RJ-45 connector. The clock signals and pin
assignments are printed on the rear panel of the CG635 in the CLOCK OUT section.
