AD9953-PCB Analog Devices, Inc., AD9953-PCB Datasheet - Page 21

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

completes a cycle, the RAM address generator increments to the
next address, and the timer reloads the ramp rate bits and con-
tinues counting down. This sequence continues until the RAM
address generator has incremented to an address equal to the
RAM segment final address bits of the current RSCW. Upon
reaching this terminal address, the RAM address generator
reloads the RAM segment beginning address bits and the
sequence repeats.
The sequence of circulating through the specified RAM
addresses repeats for as long as the part is programmed for this
mode. The no-dwell bit is a Don’t Care in this mode.
RAM Controlled Modes of Operation Notes and Summary
Notes:
1)
2)
3)
The AD9953 offers five modes of RAM controlled operation
(see Table 6).
Table 6. RAM Modes of Operation
RSCW<7:5>
(Binary)
000
001
010
011
100
101, 110, 111
Internal Profile Control
The AD9953 offers a mode in which a composite frequency
sweep can be built, for which the timing control is software
programmable. The internal profile control capability disen-
gages the Profile<1:0> pins and enables the AD9953 to take
control of switching between profiles. Modes are defined that
allow continuous or single burst profile switches for three
combinations of profile selection bits. These are listed in Table
7. When any of the CFR1<29:27> bits are active, the
The user must ensure that the beginning address is lower
than the final address.
Changing profiles or issuing an I/O UPDATE automatically
terminates the current sweep and starts the next sweep.
Setting the RAM destination bit true such that the RAM
output drives the phase offset adder is valid. While the
above discussion describes a frequency sweep, a phase
sweep operation is also available.
Mode
Direct Switch
Ramp Up
Bidirectional
Ramp
Continuous
Bidirectional
Ramp
Continuous
Recirculate
Open
Notes
No Sweeping, Profiles
Valid, No Dwell Invalid
Sweeping, Profiles Valid,
No Dwell Valid
Sweeping, Profile <0> Is a
Direction Control Bit, No
Dwell Invalid
Sweeping, Profiles Valid,
No Dwell Invalid
Sweeping, Profiles Valid,
No Dwell Invalid
Invalid Mode—Default To
Direct Switch
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When any of the CFR1<29:27> bits are active, the
internal profile control mode is engaged. Internal profile control
is only valid when the device is operating in RAM mode. There
is no internal profile control for linear sweeping operations.
When the internal profile control mode is engaged, the RAM
segment mode control bits are Don’t Care and the device oper-
ates all profiles as if these mode control bits were programmed
for ramp-up mode. Switching between profiles occurs when the
RAM address generator has exhausted the memory contents for
the current profile.
Table 7. Internal Profile Control
CFR1<29:27>
(Binary)
000
001
010
011
100
101
110
111
A single burst mode is one in which the composite sweep is
executed once. For example, assume the device is programmed
for ramp-up mode and the CFR1<29:27> bits are written to
Logic 010(b). Upon receiving an I/O UPDATE, the internal
control logic signals the device to begin executing the ramp-up
mode sequence for Profile 0. Upon reaching the RAM segment
final address value for Profile 0, the device automatically
switches to Profile 1 and begins executing that ramp-up
sequence. Upon reaching the RAM segment final address value
for Profile 1, the device automatically switches to Profile 2 and
begins executing that ramp-up sequence. When the RAM seg-
ment final address value for Profile 2 is reached, the sequence is
over and the composite sweep has completed. Issuing another
I/O UPDATE restarts the burst process.
A continuous internal profile control mode is one in which the
composite sweep is continuously executed for as long as the
device is programmed into that mode. Using the example above,
except programming the CFR1<29:27> bits to Logic 101(b), the
operation would be identical until the RAM segment final
address value for Profile 2 is reached. At this point, instead of
stopping the sequence, it repeats, starting with Profile 0.
Mode Description
Internal Control Inactive
Internal Control Active, Single Burst, Activate
Profile 0, Then 1, Then Stop
Internal Control Active, Single Burst, Activate
Profile 0, Then 1, Then 2, Then Stop
Internal Control Active, Single Burst, Activate
Profile 0, Then 1, Then 2, Then 3, Then Stop
Internal Control Active, Continuous, Activate
Profile 0, Then 1, Then Loop Starting 0
Internal Control Active, Continuous, Activate
Profile 0, Then 1, Then 2, Then Loop Starting 0
Internal Control Active, Continuous, Activate
Profile 0, Then 1, Then 2, Then 3, Then Loop
Starting 0
Invalid
AD9953