Operation 24
CG635 Synthesized Clock Generator
where f
DDS
is frequency being output by the DDS chip, and f
OUT
is the current output
frequency.
The parameters FT3, FT2, FT1, and FT0 define the current frequency tuning word for the
DDS chip. They satisfy the equation,
)
MHz
20
(
2
0
65536
1
65536
2
65536
3
64
2
3
×
×
+
×
+
×
+
×
=
M
FT
FT
FT
FT
f
DDS
,
where M is the DDS clock multiplier which is normally set to 5. See the Circuit
Description chapter for more information about the operation of the RF synthesizer and
DDS chip.
PRBS ON/OFF
If the PRBS option is installed, the PRBS ON function enables the PRBS output, and the
PRBS OFF disables it. The CG635 will briefly display ‘PRBS on’ or ‘PRBS off’,
respectively, when the functions are accessed.
If the PRBS option is not installed, the CG635 will briefly display ‘no PRBS.’
The PRBS on/off state is saved when instrument settings are saved. If PRBS is installed,
the current status (on/off/disabled) of the PRBS can viewed via the STATUS function. A
status of ‘disabled’ indicates that the PRBS is requested on but disabled because the
current frequency is too high.
FREQ/2, FREQx2
The functions FREQ/2 and FREQx2 cause the CG635 to decrease or increase the current
frequency by a factor of two. They also force the CG635 to display frequency.
REL
ș
= 0
This function defines the current phase to be zero degrees. It does not affect the output. It
also forces the CG635 to display phase.
ș
+ 90°
This function advances the current phase by 90°. It also forces the CG635 to
display phase.
GPIB
This function enables the GPIB remote interface and disables the RS-232 remote
interface. The CG635 will briefly display ‘Enabled’ after enabling the interface. This
function is not executed until the user presses ‘Hz’. The GPIB LED in the INTERFACE
section of the front panel will be on when GPIB is the selected interface.
