AD9953-PCB Analog Devices, Inc., AD9953-PCB Datasheet - Page 23

• Manufacturer Part Number: AD9953-PCB
• Description: 400 Msps 14-bit, 1.8v Cmos Direct Digital Synthesizer
• Manufacturer: Analog Devices, Inc.

OSK Ramp Rate Timer
The OSK ramp rate timer is a loadable down counter, which
generates the clock signal to the 14-bit counter that generates
the internal scale factor. The ramp rate timer is loaded with the
value of the ASFR every time the counter reaches 1 (decimal).
This load and countdown operation continues for as long as the
timer is enabled, unless the timer is forced to load before reach-
ing a count of 1.
If the load OSK timer bit (CFR1<26>) is set, the ramp rate timer
is loaded upon an I/O UPDATE or upon reaching a value of 1.
The ramp timer can be loaded before reaching a count of 1 by
three methods.
DDS CORE
AMPLITUDE SCALE
FACTOR REGISTER
COS(X)
(ASF)
0
1
Figure 20. On-Off Shaped Keying Block Diagram
0
OSK ENABLE
FACTOR GENERATOR
CFR<25>
OUT
OSK PIN
INC/DEC ENABLE
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AUTO SCALE
UP/DN
HOLD
TO DAC
SYNC_CLK
The first method of loading is by changing the OSK input pin.
When the OSK input pin changes state, the ASFR value is
loaded into the ramp rate timer, which then proceeds to count
down as normal.
The second method in which the sweep ramp rate timer can be
loaded before reaching a count of 1 is if the load OSK timer bit
(CFR1<26>) is set and an I/O UPDATE is issued.
The third method in which the sweep ramp rate timer can be
loaded before reaching a count of 1 is when going from the
inactive auto shaped on-off keying mode to the active auto
shaped on-off keying mode; that is, when the sweep enable bit is
being set.
AUTO DESK
CFR1<24>
ENABLE
RAMP RATE TIMER
LOAD OSK TIMER
CFR1<26>
AMPLITUDE RAMP
RATE REGISTER
LOAD
(ASF)
DATA
EN
CLOCK
AD9953