AD9854SLASHPCB datasheet(37/44 Pages) AD

37 / 44 page

AD9854

–37–

REV. 0

The control software for the AD9854/PCB evaluation board is

provided on a CD. This brief set of instructions should be used

in conjunction with the AD9854/PCB evaluation board schematic.

Several numerical entries, such as frequency and phase infor-

mation, require that the ENTER key by pressed to register

that information.

1. Select the proper printer port. Click the “Parallel Port” selec-

tion in the menu bar. Select the port that matches your PC.

If unknown, experiment by performing the following on the

selected port. With the part powered up, properly clocked and

connected to the PC, select a port and go to the “Mode and

Frequency” menu and click the “Reset DUT and Initialize

Registers” button. Then go to the “Clock and Amplitude”

menu. Once there, click the box next to “Bypass Inverse Sinc

Filter” . . . a check mark will appear in the box . . . next click

the button “Send Control Info to DUT.” If the proper port

has been selected, the supply current going to the AD9854/

PCB evaluation board should drop by approximately 1/3 when

the inverse sinc ﬁlters are bypassed. Conversely, the supply

current will increase approximately 1/3 when the inverse sinc

ﬁlters are engaged.

2. Normal operation of the AD9854/PCB evaluation board be-

gins with a master reset. Many of the default register values

after reset are depicted in the software “control panel.” The

reset command sets the DDS output amplitude to minimum

and 0 Hz, 0 phase-offset as well as other states listed in the

AD9854 Register Layout table in the preliminary data sheet.

3. The next programming block should be the “Reference Clock

and Multiplier” since this information is used to determine

the proper 48-bit frequency tuning words that will be entered

and calculated later.

4. The output amplitude defaults to the 12-bit straight binary

multiplier values of the I and Q multiplier registers of 000hex

and no output should be seen from the DACs. User should

now set both multiplier amplitudes in the Output Amplitude

window to a substantial value, such as FFFhex. You may

bypass the digital multiplier by clicking the box “Output

Amplitude is always Full-Scale” but experience has shown

that doing so does not result in best SFDR. It is interesting

to note that best SFDR, as much as 11 dB better, is obtained

by routing the signal through the digital multiplier and “backing

off” on the multiplier amplitude. For instance, FC0 hex

produces less spurious signal amplitude than FFF hex. Its a

repeatable phenomenon that should be investigated exploited

for maximum SFDR (spurious-free dynamic range).

5. 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 is

doing in response to programming commands.

Applications assistance is available for the AD9854, the

AD9854/PCB evaluation board, and all other Analog Devices

products. Please call 1/800-ANALOGD.

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