AD9857: FUD signal

Document created by analog-archivist Employee on Feb 23, 2016
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Subject: AD9857 Digital Up Converter and its evaluation board.
1) The rising edge of the FUD signal would to transfer the profile registers
content in the DDS accumulator. Why Does the FUD signal in the board change its
state continously during the data transfers ?
2) Is the reset signal anabling necessary any time the frequency is changed ?

 

1) The rising edge of the FUD signal would to transfer the profile registers
content in the DDS accumulator. Why Does the FUD signal in the board change its
state continously during the data transfers ?
Pin 79 on the AD9857 has two functions. In single tone more, pin 79 is an input
and acts as a Frequency update pin (FUD) and operates just as you describe.
When not in Single-Tone Mode, this pin is an output signal that should be used
as a clock to synchronize the acceptance of the 14-bit parallel data words on
Pins D13–D0.
When in quadrature modulation mode, the part is expecting I and Q baseband data
to be clocked into the 14bit parallel data bus.

2) Is the reset signal enabling necessary any time the frequency is changed ?
No, when in single tone mode, you can change the frequency tuning word at any
time via the serial port and output of the DDS will be phase continuous.

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