AD9854ASQ Analog Devices Inc, AD9854ASQ Datasheet - Page 44

• Manufacturer Part Number: AD9854ASQ
• Manufacturer: Analog Devices Inc

Specifications of AD9854ASQ

• Lead Free Status / RoHS Status: Not Compliant

AD9854
and W8 3-pin header switches. The configuration described in
the Observing the Filtered IOUT1 and the Filtered IOUT2
section must be used. Follow Steps 1 through 4 in that section,
and then install shorting jumpers on Pin 1 and Pin 2 (top two
pins) of the 3-pin W2 and W8 headers.
The user can elect to change the R
1.95 kΩ to receive a more robust signal at the comparator
inputs. This decreases jitter and extends the comparator
operating range. The user can accomplish this by installing a
shorting jumper at W6, which provides a second 3.9 kΩ chip
resistor (R20) in parallel with the provided R2.
USING THE PROVIDED SOFTWARE
The evaluation software is provided on a CD. This brief set of
instructions should be used in conjunction with the AD9852 or
AD9854 data sheet and the AD9852/AD9854 evaluation board
schematic.
The CD contains the following:
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Several numerical entries, such as frequency and phase infor-
mation, require users to press Enter to register the information.
For example, if a new frequency is input but does not take effect
when Load is clicked, the user probably neglected to press Enter
after typing the new frequency information.
Normal operation of the AD9852/AD9854 evaluation board
begins with a master reset. Many of the default register values
after reset are depicted in the software control panel. The reset
The AD9852/AD9854 evaluation software
AD9854 evaluation board instructions
AD9854 data sheet
AD9854 evaluation board schematics
AD9854 PCB layout
SET
resistor, R2, from 3.9 kΩ to
Rev. D | Page 44 of 52
command sets the DDS output amplitude to minimum and
0 Hz, zero phase-offset as well as other states that are listed in
the AD9852/AD9854 Register Layout table in the data sheet.
The next programming block should be the reference clock and
multiplier because this information is used to determine the
proper 48-bit frequency tuning words that are entered and
calculated later.
The output amplitude defaults to the 12-bit straight binary
multiplier values of the I, or cosine, multiplier register of 000 hex,
and no output (dc) should be seen from the DAC. Set the multiplier
amplitude in the Output Amplitude dialog box to a substantial
value, such as FFF hex. The digital multiplier can be bypassed by
selecting Output Amplitude Is Always Full Scale, but experience
has shown that doing so does not result in best spurious-free
dynamic range (SFDR). Best SFDR, as much as 11 dB better, is
obtained by routing the signal through the digital multiplier and
then reducing the multiplier amplitude. For instance, FC0 hex
produces less spurious signal amplitude than FFF hex. It is an
exploitable and repeatable phenomenon that should be investigated
in your application if SFDR must be maximized. This phenomenon
is more readily observed at higher output frequencies, where
good SFDR becomes more difficult to achieve.
Refer to this data sheet and evaluation board schematic to
understand all the functions of the AD9854 available to the user
and to gain an understanding of what the software does in response
to programming commands.
SUPPORT
Applications assistance is available for the AD9854, the AD9854
PCB evaluation board, and all other Analog Devices products.
Please call 1-800-ANALOGD or visit www.analog.com/dds.